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Tropical grassy biomes: Misunderstood, neglected, and under threat
Abstract
Tropical grassy biomes (TGBs) are globally extensive, provide critical ecosystem services, and influence the earth-atmosphere system. Yet, globally applied biome definitions ignore vegetation characteristics that are critical to their functioning and evolutionary history. Hence, TGB identification is inconsistent and misinterprets the ecological processes governing vegetation structure, with cascading negative consequences for biodiversity. Here, we discuss threats linked to the definition of TGB, the Clean Development Mechanism (CDM) and Reducing Emissions from Deforestation and Forest Degradation schemes (REDD+), and enhanced atmospheric CO2, which may facilitate future state shifts. TGB degradation is insidious and less visible than in forested biomes. With human reliance on TGBs and their propensity for woody change, ecology and evolutionary history are fundamental to not only the identification of TGBs, but also their management for future persistence.
... That assessment demonstrated that prescribed EDS fire management to reduce LDS wildfire extent and resultant emissions met key technical criteria: LDS fine fuels tended to be greater than EDS fuels given seasonal leaf litter inputs; LDS fires tended to be significantly more severe and combust more fuels; methane and nitrous oxide emission factors were essentially equivalent in EDS and LDS periods under cured fuel conditions. The latter authors noted, however, that: (1) application of a fairly conservative, low severity savanna burning approach is not appropriate in situations at risk of exacerbating woody encroachment and associated loss of open habitat and dependent biodiversity (Parr et al. 2014;Veldman et al. 2015;Abreu et al. 2017;Bond 2019); (2) there are various significant key implementation challenges (e.g. national regulatory issues, project governance arrangements, equity and rights concerns, capacity building opportunities, market instruments) that need to be addressed to progress development of savanna burning methods for incentivising sustainable fire management and supporting community livelihoods in wildfire-dominated southern African savannas. ...
... Other vegetation types excluded from our methods application include Afromontane, Evergreen dry forest, Itigi thicket formations (after Timberlake and Chidumayo 2011) and more localised embedded vegetation types associated with termitaria, riparian systems, omuramba (dune swales), and seasonally flooded (dambo) and freely draining grasslands systems. Dambos, omuramba and natural grasslands occur extensively in various southern African landscape settings but are excluded from the proposed emissions abatement methodology given that prescribed more conservative EDS fire management activities would likely result in woody encroachment and thickening, and hence significant deleterious impacts on floristic and wildlife species diversity associated with loss of open grazing (O'Connor et al. 2014;Parr et al. 2014) and avian habitat (Sirami and Monadjem 2012). However, as noted in the discussion, EDS prescribed fire management in adjacent woodland savannas can allow safe application of more intense fires in embedded open grassy habitats. ...
... First, application of a fairly conservative, low-severity EDS fire management approach is not appropriate in grassland situations at risk of exacerbated woody encroachment and associated loss of habitat and dependent biodiversity (e.g. Parr et al. 2014;Veldman et al. 2015). However, strategically undertaken savanna burning projects can provide a funded, operational framework to assist with delivering a range of objectives including, for example, safe application of intense fires in a matrix of reduced fuel loads for woody plant control and maintaining open grassy habitats . ...
Background and aims. To assess development of a robust emissions accounting framework for expansive miombo woodland savannas covering ~2 million km 2 of southern Africa that typically are burnt under relatively severe late dry season (LDS) conditions. Methods. A detailed site-based study of fuel accumulation, combustion and greenhouse gas (GHG) emission factor parameters under early dry season (EDS) and LDS conditions along a central rainfall-productivity and associated miombo vegetation structural and floristics gradient, from lower rainfallsites in northern Botswana to higher rainfall sites in northern Zambia. Key results. Assembled field data inform core components of the proposed emissions reduction framework: fuel and combustion conditions sampled across the vegetation/productivity gradient can be represented by three defined Vegetation Fuel Types (VFTs); fuel accumulation, combustion and emissions parameters are presented for these. Applying this framework for an illustrative case, GHG emissions (t CO 2-e) from EDS fires were one-third to half those of LDS fires per unit area in eligible miombo VFTs. Conclusions. Our accounting framework supports undertaking EDS fire management to significantly reduce emissions and, realistically, burnt extent at landscape scales. We consider application of presented data to development of formal emissions abatement accounting methods, linkages with potential complementary woody biomass and soil organic carbon sequestration approaches, and necessary caveats concerning implementation issues.
... Drawing on the definition used by the Food and Agriculture Organization (FAO) of the United Nations (UN), WRI and the IUCN (among others) define forests as areas that are covered in trees with canopy cover of at least 10% (1). But this definition has been criticized (4,5) because it can be used to erroneously classify open systems with trees, such as savanna, as forest. ...
... There is, therefore, the potential for tree planting to occur in nonforested systems, such as tropical grasslands and savannas, because they are frequently misclassified as forest (4,6) or tree cover levels are deemed below potential given the climate and soils (1). FLR considers increases in woody cover as desirable with a focus on the regrowth of trees on the landscape (1), and seldom as something undesirable. ...
... FLR considers increases in woody cover as desirable with a focus on the regrowth of trees on the landscape (1), and seldom as something undesirable. Yet, restoration actions that increase tree cover in nonforested systems can be problematic because high tree cover can degrade them (4). Planting trees in grassy systems increases canopy cover and reduces light with consequent structural, compositional, and functional changes to the understory; in some grassy systems, this can result in wholesale biodiversity loss, notably of shade-intolerant species associated with open habitats (7), as well as changes in ecosystem functioning, declines in critical ecosystem services (e.g., reduced water availability, restricted access to food and medicinal resources), and even unintended climate warming due to reduced albedo (4,6). ...
Across Africa, vast areas of nonforest are threatened by inappropriate restoration in the form of tree planting
... The ecological interpretation of tropical grassy ecosystems has evolved during the late 20th century, moving away from the simple paradigm of Clementsian succession and towards the recognition of disturbance-driven open canopy vegetation mosaics as not only ancient and natural biodiversity ecosystems but also valued providers of ecosystem services including carbon storage, water and cultural services (Bond, 2019;Parr et al., 2014). The concept of old-growth grasslands has proved especially controversial in Madagascar, where the traditional conservation narrative has relied on Perrier de la Bâthie's erroneously high estimates of tree cover loss (Bond et al., 2023;Richard, 2022). ...
... Grassy ecosystem areas have not been the subject of dedicated research attention to date, leading to a lack of grass diversity datasets. According to global reviews of old-growth grasslands and their ecology, a prehuman grass flora would be expected to have (1) the presence of regionally unique (endemic) species of Poaceae (Parr et al., 2014;Veldman et al., 2015); (2) Poaceae local species richness and composition that varies with habitat and soil type (Pielou, 1975;Wilsey, 2018); and (3) Poaceae regional indigenous (native) species richness comparable to the previously studied likely pre-human grass floras of the southern highlands (Parr et al., 2014;Veldman et al., 2015). In order to assess the grass flora of the Boeny Region against these three criteria, we carried out the first inventory of the grasses in the northwest of Madagascar to characterise the habitats of each species, determine which species are endemic, and compare this grass flora assessment to the grass floras of Itremo and Isalo in the south-central highlands. ...
... Grassy ecosystem areas have not been the subject of dedicated research attention to date, leading to a lack of grass diversity datasets. According to global reviews of old-growth grasslands and their ecology, a prehuman grass flora would be expected to have (1) the presence of regionally unique (endemic) species of Poaceae (Parr et al., 2014;Veldman et al., 2015); (2) Poaceae local species richness and composition that varies with habitat and soil type (Pielou, 1975;Wilsey, 2018); and (3) Poaceae regional indigenous (native) species richness comparable to the previously studied likely pre-human grass floras of the southern highlands (Parr et al., 2014;Veldman et al., 2015). In order to assess the grass flora of the Boeny Region against these three criteria, we carried out the first inventory of the grasses in the northwest of Madagascar to characterise the habitats of each species, determine which species are endemic, and compare this grass flora assessment to the grass floras of Itremo and Isalo in the south-central highlands. ...
Societal Impact Statement
Madagascar's children are taught that their ancestors destroyed the vast ancient forest, giving rise to modern grasslands, a misleading myth that continues to undermine people's relationship with nature. Replacing this myth with a more nuanced and accurate narrative around grassy ecosystems is fundamental to building a more positive relationship between Madagascar's people and ecosystems, a process that is necessary to build modern conservation practice and environmental governance. The data we present are consistent with a pre‐human grass flora in the region, suggesting the local grassy ecosystems should not be written off as fully anthropogenic and undesirable but are instead in need of recognition and further research attention.
Summary
Grassy ecosystems cover over a quarter of dry land, with mosaics of old‐growth and recently formed anthropogenic systems appearing superficially similar to an uninformed observer. Grasses are part of a deep web of historic relationships between grassy ecosystems and local people.
We collect and compile the first list of grass species (Poaceae) in north‐west Madagascar in order to make an initial evidence assessment for a pre‐human grass flora. Field surveys and voucher specimen collections were carried out. Specimen identification was performed using morphological character comparison with reference specimens, literature and personal knowledge of grasses from other parts of Madagascar.
Seventy species are recorded and assigned to 44 genera. The species list is compared with regional grass checklists from central and south‐central Madagascar. Thirty‐five grasses are unique to Mahajanga, comprising 19% of the multi‐region species pool analysed; the regional species richness is comparable to that of the highlands.
The main subfamilies represented are the Panicoideae (64%) and Chloridoideae (29%). Seven species are endemic to Madagascar, reflecting their evolutionary origins on the island. Many of the species are found in multiple types of habitat and substrate, while others are restricted to limited areas and habitats, and local species richness varies significantly with habitat and soil. The main disturbance regimes driving species occurrence include fire and grazing, possibly partly reflecting similar disturbances prior to human arrival. The patterns observed in the grass flora of north‐western Madagascar are overall congruent with a pre‐human grass flora.
... At best, mixed tree-grass vegetation may be labelled as savanna, woodland or wooded grassland, with the condition that tree or 'forest' cover is > 10% (e.g. Table 2 in Yang et al., 2017), ignoring the fact that tropical grasslands and savannas are more functionally similar to each other than either is to forests (Parr et al., 2014;Stevens et al., 2022). Hence the exaggeration of forest cover in maps based on vegetation structure alone. ...
... Even if a pixel at 30 m resolution has tree height > 5 m and tree cover > 10% it can still be naturally open, e.g. (Parr et al., 2014;Pausas and Bond, 2022) covering 20-25% of Earth's land surface (Ramankutty and Foley, 1999;Bond, 2022). A defining characteristic of TGBs is the herbaceous layer dominated by C 4 grasses and sedges (Frost et al., 1986). ...
... Savannas are maintained by interactions between consumers (mainly fire and herbivores) and resources (soil nutrients and precipitation), unlike forests, which are maintained mainly by resources, especially light (Charles-Dominique et al., 2018;Pausas and Bond, 2021;Stevens et al., 2022). Therefore, woody species in savannas and forests are functionally very different (Parr et al., 2014;Pausas and Bond, 2021). Savanna species are shadeintolerant, fire-tolerant and tolerant of damage by large mammal herbivores, whereas forest species are not (Charles-Dominique et al., 2018;Scogings and Sankaran, 2020;Stevens et al., 2022). ...
... The overarching theme of this dissertation is co-production of science for the conservation of grasslands threatened by woody encroachment. Grassland biomes across the globe are experiencing unsustainable trends of tree invasion by native and non-native species that are driving an ongoing biome transition process (Parr et al. 2014;Stevens et al. 2017;Jones et al. 2020;. Conservation in an era of biome transitions demands new and adaptive approaches that go beyond disciplinary traditions of natural resource management. ...
... Globally, low abundances of woody plants in arid and semi-arid grassland ecosystems have been interpreted as evidence that these areas have little to no potential for woody encroachment (Bond et al., 2003(Bond et al., , 2005Lehmann et al., 2014;Sankaran et al., 2005;Scholtz et al., 2018). However, our results show no support that sparsely distributed woody plants in the Sandhills are reflective of establishment-based constraints. ...
... Halting and reversing woody encroachment is therefore a central goal in grassland conservation van Wilgen et al. 2012a;Twidwell et al. 2013c). The risks of failing to halt woody plant encroachment and conserve remaining grasslands include a loss of biodiversityParr et al. 2014), reduced freshwater supply and quality (Jackson et al. 2005; Zou et al. 2018), increased wildfire hazard (de Wit et al. 2001; Donovan et al. 2020b), reduced food production (Anadon et al. 2014), and endangerment of livelihoods and human well-being (Swallow and Mwangi 2008; Twidwell et al. 2013c). These risks are well known and justify major conservation expenditures in excess of tens of millions of dollars per year to clear woody plants and stabilize and restore grassland ecosystem services(Marais et al. 2004;Tanaka et al. 2011; Twidwell et al. 2013a). ...
Confronting biome-scale threats in the 21st century will require new and adaptive approaches for conservation. The overarching theme of this dissertation is co-produced science for the conservation of grasslands threatened by woody encroachment. Each chapter reflects a research question co-developed by scientists and managers to better understand and manage the threat of woody encroachment. First, I examine the dimensions of grassland risk through a series of field studies. Risk is the outcome of a grassland’s sensitivity and exposure to encroaching woody plants. Sensitivity reflects the rate and ease of grassland transition to a woodland, while, exposure is driven by propagule sources and their dispersal. My findings demonstrate the importance of exposure in driving patterns of encroachment and provide a basis for managing the spatial dimensions of exposure. Second, I assess the potential impacts of plant invasions in grasslands using a participatory ecosystem service assessment. Findings illustrate the potential for severe impacts associated with woodland transitions driven by a native-invasive tree compared to non-native invasive weeds. Third, I assess the sustainability of grassland conservation approaches, including the lifespan of restoration treatments. Overall, I find unsustainable trends of grassland loss to encroachment across a network of priority conservation areas. Conservation efforts tended to be outpaced by encroachment of intact grasslands and re-encroachment of sites undergoing restoration, which rapidly transition back to a woodland without follow-up management. Large-scale fire management provided the only example of counteracting regional trends of encroachment and serves as a model for improving conservation efforts in other grasslands threatened by encroachment. However, the viability of this approach will likely depend upon broader acceptance of the role of prescribed fire in grasslands. To this end, I developed fire management scenarios to contrast air-quality outcomes of large-scale fire management versus those of fire exclusion. The scenarios illustrate the inevitable nature of fire in flammable ecosystems and provide a basis for communicating the role of prescribed fire in avoiding long-term consequences associated with wildfire.
... Notably, these regions currently display some of the most pronounced cultural disparities within a given biome. This variability in human impact arises from significant differences in population density, extent and intensity of agriculture, fate of production (from subsistence to industrial commodity production), wealth and cultural or ideological values (Baldi and Jobbágy 2012, Parr et al. 2014, Schröder et al. 2021, Camino et al. 2023). Importantly, their natural resources face mounting pressures as a result of population growth, rising affluence and their integration into global markets (Parr et al. 2014, Gasparri et al. 2016, Buchadas et al. 2022. ...
... This variability in human impact arises from significant differences in population density, extent and intensity of agriculture, fate of production (from subsistence to industrial commodity production), wealth and cultural or ideological values (Baldi and Jobbágy 2012, Parr et al. 2014, Schröder et al. 2021, Camino et al. 2023). Importantly, their natural resources face mounting pressures as a result of population growth, rising affluence and their integration into global markets (Parr et al. 2014, Gasparri et al. 2016, Buchadas et al. 2022. All these attributes collectively shape the varying dependencies of individuals on natural resources across regions, alongside their capacity to harness these resources (Pratzer et al. 2024). ...
Dry subtropical (DST) regions that share similar climatic and topographic conditions exhibit today significant disparities in population density, agricultural intensity, wealth and cultural values. In addition, they are also facing increasing pressures on their natural resources. These attributes collectively shape individuals' varying dependence on natural resources and may influence their perception of ecosystem services (ES). In this study, we conducted a systematic literature review, focusing on the DST regions, to address two main questions: 1) What is the current state, temporal trends and regional variability in scientific research on ES and 2) What are the potential drivers of the variability in ES research? Amongst the 471 publications found in our review, 53% focused on provisioning services, followed nearly equally by cultural (33%) and regulating (30%) services. Only 13% addressed more than one ES category and approximately 33% mentioned economic valuation. Our study reveals that research on ES in the dry subtropics experienced a significant increase from 2005 onwards. Approximately 45% of the publications included the term 'ecosystem service' and its frequency has risen substantially over time. Most publications primarily focus on African dry subtropics (over 60%), followed by South and North American ones. Publications from southern Asia and NE Australia were more scarce. Importantly, we found no clear relationship between the number of publications, publication density or representativeness and the variables used as indicators of human pressure (e.g. population density). Consequently, research efforts in the DST regions appear to be influenced by a diverse range of financial and institutional constraints, international research agendas, as well as the personal interests of researchers, contributing to the idiosyncratic nature of this field.
... Recent analyses of remotely sensed tree cover at global (Hirota, Holmgren, Nes, & Scheffer, 2011) and local scales (Favier et al., 2012) have shown that at intermediate rainfall (1,000-2,500 mm for Africa, Staver, Archibald, & Levin, 2011), forests and savannas can both occur and may represent alternative stable states maintained through feedbacks between fire, herbivory and canopy cover (Favier et al., 2012;Hirota et al., 2011;Staver et al., 2011). Within this rainfall range, savannas are often wrongly viewed as degraded forests (Laestadius et al., 2011), while they actually are ancient ecosystems with a long evolutionary history (Parr, Lehmann, Bond, Hoffmann, & Andersen, 2014;Veldman et al., 2015) almost entirely distinct in species composition from forests (Swaine, Hall, & Lock, 1976). ...
... Miombo woodland)", "savanna woodland", "tree savanna" and "shrub savanna" agreed in Yangambi (Aubréville, 1957) in what may be thought of as the savanna biome sensu latu. We specifically excluded "grass savanna", true grasslands that lack trees over large areas and that are now considered as a separate biome (Parr et al., 2014). We note that in his vegetation map of Africa, White (1983) avoided "savanna" but instead used the term "wooded grassland". ...
Aim
In tropical Africa, savannas cover huge areas, have high plant species richness and are considered as a major natural resource for most countries. There is, however, little information available on their floristics and biogeography at the continental scale, despite the importance of such information for our understanding of the drivers of species diversity at various scales and for effective conservation and management. Here, we collated and analysed floristic data from across the continent in order to propose a biogeographical regionalization for African savannas.
Location
We collated floristic information (specifically woody species lists) for 298 samples of savanna vegetation across Africa, extending from 18° N to 33° S and from 17° W to 48° E.
Taxa
We focused on native woody species.
Methods
We used ordination and clustering to identify the floristic discontinuities and gradual transitions across African savannas. Floristic relationships, specificity and turnover, within and between floristic clusters, were analysed using a (dis‐)similarity‐based approach.
Results
We identified eight floristic clusters across African savannas which in turn were grouped into two larger macro‐units. Ordinations at species and genus levels showed a clear differentiation in woody species composition between the North/West macro‐unit and the South/East macro‐unit. This floristic discontinuity matches to the High (i.e. N&W) and Low (S&E) division of Africa previously proposed by White (1983) and which tracks climatic and topographical variation. In the N&W savannas, the floristic gradient determined by rainfall was partitioned into the Sudanian (drier) and Guinean (wetter) clusters. Within the highly heterogeneous S&E savannas and woodlands, six clusters were identified: Ugandan, Ethiopian, Mozambican, Zambezian, Namibian and South African.
Main conclusions
The proposed pan‐African classification of savannas and woodlands might assist the development of coordinated management and conservation policies.
... (Parr et al., 2014;Aleman & Staver, 2018). Grasslands are dominated by grasses with no or very weak woody cover, while savannas are characterized by a mixture of woody species, grasses, and forbs, with a discontinuous tree canopy and a continuous grass understory.The maintenance of savannas relies on specific mechanisms and disturbances that contribute to their open canopy structure and species diversity (Scholes & Archer, 1997). ...
... In addition, forest encroachment into grasslands and savannas is a global trend that is significantly altering the landscape structure and ecological dynamics of these ecosystems (Stevens et al., 2017). Forests, savannas and grasslands often form a complex matrix in tropical climates, creating diverse habitats that support local livelihoods and foster biodiversity (Parr et al., 2014). However, recent observations indicate a rapid shift, with forests increasingly encroaching upon savannas in regions such as sub-Saharan Africa, homogenizing the formerly-complex forest-savanna mosaic (Mitchard et al., 2011;Venter et al., 2018;Stevens et al., 2017) Forest encroachment is a multifaceted phenomenon that is driven by various factors, including climate change, human activities, and changes in species composition (Stevens et al., 2017;Venter et al., 2018;Devine et al., 2017). ...
Forest encroachment over savannas has been recurrently reported in the tropics over the last decades, especially in northern tropical Africa. However, process-based, spatially-explicit modelling of the phenomenon is still trailing broad scale empirical observations. In this paper, we used remotely-sensed diachronic data from Central Cameroon to calibrate a simple reaction-diffusion model, embodying dynamical interactions between grass and woody biomasses in the savanna biome.
Landsat satellite image series over the Mpem and Djim National Park witnessed a dramatic extension of forest over the last five decades and our estimates of forest front speeds based on randomly sampled transects indeed yielded higher values (5-7 meters per year) than in the existing literature.
We used simulations of the model to provide the first hitherto estimates of woody biomass dispersal coefficients. Since the region under study did not provide examples of savanna progression, estimates of grass dispersal proved inconsistent and we reverted to literature-based historical data to reach rough estimates. This paper demonstrates that broad scale remote sensing data allows for calibrating simple reaction-diffusion models of vegetation dynamics in the savanna biome. Once calibrated, such models become a general baseline of expected changes and a valuable tool to understand how spatial environmental factors (e.g., soil substrate) may locally modulate the overall dynamics.
... Simultaneously, rangelands are also used in carbon offset investments. These investments leverage the natural capacity of rangelands to sequester carbon, thereby contributing significantly to global carbon offset initiatives Ó The Author(s) 2024 www.kva.se/en in initiatives such as the African Forest Landscape Restoration Initiative (AFR100) threatens biodiversity, ecosystem services and human livelihood in those non-forest ecosystems (Parr et al. 2014). Soil organic carbon (SOC) and belowground carbon pools in rangelands are also undervalued (Bossio et al. 2020). ...
... One deep-lying barrier to the idea of wilder rangelands is the widespread paradigm and narrative that many of the world's rangelands, and grassy biomes they are a part of, are of anthropogenic origin (Parr et al. 2014). According to this paradigm, anthropogenic fire and/or grazing regimes have led to deforestation and created these grassy systems under climatic conditions that would naturally allow forest (Veldman 2016). ...
Rangelands face threats from climate and land-use change, including inappropriate climate change mitigation initiatives such as tree planting in grassy ecosystems. The marginalization and impoverishment of rangeland communities and their indigenous knowledge systems, and the loss of biodiversity and ecosystem services, are additional major challenges. To address these issues, we propose the wilder rangelands integrated framework, co-developed by South African and European scientists from diverse disciplines, as an opportunity to address the climate, livelihood, and biodiversity challenges in the world’s rangelands. More specifically, we present a Theory of Change to guide the design, monitoring, and evaluation of wilder rangelands. Through this, we aim to promote rangeland restoration, where local communities collaborate with regional and international actors to co-create new rangeland use models that simultaneously mitigate the impacts of climate change, restore biodiversity, and improve both ecosystem functioning and livelihoods.
... While a multitude of drivers of global change are transforming Earth's grassy biomes, land-use change has emerged as an acute and widespread cause of biodiversity loss in tropical savannas (Lapuz et al., 2021;Newbold et al., 2016;Parr et al., 2014). Much of our understanding on the ecological consequences of land-use change for tropical savanna plant communities comes from studies in South America (e.g., Almeida et al., 2011;Cava et al., 2018;Laste et al., 2019) or has been inferred from studies of subtropical savannas in North America (Kirkman et al., 2004), southern Africa and ...
... While the limits of the tropical savanna biome span approximately 100 to 2500 mm MAP and vary by continent, most savannas occur in the range of 500 to 2000 mm MAP (Lehmann et al., 2011). Because these mesic savannas of intermediate rainfall rely on fire and herbivory to prevent forest formation (Hoffmann et al., 2012;Murphy & Bowman, 2012), they are often misperceived as degraded forests and undervalued in conservation initiatives (Parr et al., 2014;Veldman, 2016). Furthermore, the precipitation range of mesic savannas is highly suitable for growing crops and trees, making them attractive targets for agricultural expansion (Strassburg et al., 2017) and afforestation . ...
The consequences of land‐use change for savanna biodiversity remain undocumented in most regions of tropical Asia. One such region is western Maharashtra, India, where old‐growth savannas occupy a broad rainfall gradient and are increasingly rare due to agricultural conversion and afforestation.
To understand the consequences of land‐use change, we sampled herbaceous plant communities of old‐growth savannas and three alternative land‐use types: tree plantations, tillage agriculture and agricultural fallows (n = 15 sites per type). Study sites spanned 457 to 1954 mm of mean annual precipitation—corresponding to the typical rainfall range of mesic savannas globally.
Across the rainfall gradient, we found consistent declines in old‐growth savanna plant communities due to land‐use change. Local‐scale native species richness dropped from a mean of 12 species/m² in old‐growth savannas to 8, 6 and 3 species/m² in tree plantations, fallows and tillage agriculture, respectively. Cover of native plants declined from a mean of 49% in old‐growth savannas to 27% in both tree plantations and fallows, and 4% in tillage agriculture. Reduced native cover coincided with increased cover of invasive species in tree plantations (18%), fallows (18%) and tillage agriculture (3%).
In analyses of community composition, tillage agriculture was most dissimilar to old‐growth savannas, while tree plantations and fallows showed intermediate dissimilarity. These compositional changes were driven partly by the loss of characteristic savanna species: 65 species recorded in old‐growth savannas were absent in other land uses. Indicator analysis revealed 21 old‐growth species, comprised mostly of native savanna specialists. Indicators of tree plantations (nine species) and fallows (13 species) were both invasive and native species, while the two indicators of tillage agriculture were invasive. As reflective of declines in savanna communities, mean native perennial graminoid cover of 27% in old‐growth savannas dropped to 9%, 7%, and 0.1% in tree plantations, fallows and tillage agriculture, respectively.
Synthesis. Agricultural conversion and afforestation of old‐growth savannas in India destroys and degrades herbaceous plant communities that do not spontaneously recover on fallowed land. Efforts to conserve India's native biodiversity should encompass the country's widespread savanna biome and seek to limit conversion of irreplaceable old‐growth savannas.
... Planting indigenous forest species to replace agricultural fields can enhance ecological values by improving regional biodiversity and ecosystem integrity. In contrast, establishing commercial tree species in place of natural grasslands or other unique vegetation can reduce biodiversity and ecological values (Parr et al., 2014). ...
... Natural grasslands for example, have been extensively converted to croplands, pastures, agroforestry and production forestry such that much of the remaining natural grasslands are now threatened (Bond and Parr, 2010). Because of their perceived low commercial and ecological value relative to forests (Tölgyesi et al., 2021), low-productivity grasslands are prime targets for afforestation, thereby contributing to further grassland loss (Parr et al., 2014). ...
... This can be explained by feedbacks between disturbances (fire, herbivory) and grasses, which can maintain open grassy ecosystems (Bernardi et al., 2016a;de Dantas et al., 2016;Ratajczak et al., 2014;Sankaran et al., 2008;Stritih et al., 2023). In addition, recent works have emphasized that many grasslands in both tropical and temperate regions are ancient or "old-growth" ecosystems that have been neglected, and have called for their protection (Bond, 2016;Overbeck et al., 2007;Parr et al., 2014;Veldman et al., 2015). ...
... These ancient grasslands provide ecosystem services such as highvalue forage production, biodiversity, protection of watercourses, carbon sequestration in the soil, as well as cultural and social aspects (Bernardi et al., 2016b;Ding & Eldridge, 2021;Kühne et al., 2022;Singh et al., 2021). They only exist in some regions of the planet and have experienced significant losses in their extent due to conversion to other land uses or afforestation (Parr et al., 2014). Concerns about the loss of grasslands have increased in recent years due to widespread woody expansion in rangelands (Anadón et al., 2014;Cabral et al., 2003;D'Odorico et al., 2012;Mitchard & Flintrop, 2013;Ratajczak et al., 2012;Stevens et al., 2017). ...
What determines the presence (or lack) of trees in grasslands is a long-standing question in ecology. Views of trees in grasslands have shifted from generally considering grasslands as degraded forests that need to be restored, to a more recent perspective on many regions as ancient grassy biomes that have long been neglected and are, according to their climate conditions, maintained as stable biomes by internal feedbacks involving fire and/or herbivory. In addition, there are currently concerns about trends of woody expansion or "encroachment" in grasslands, i.e. potential transitions between grassy and wooded ecosystems driven by local and global changes. In this study, we use high-resolution local databases and generalized additive models (GAMLSS) to analyze the factors that determine forest cover in the Campos grasslands of Uruguay in southeastern South America. We consider climate, local conditions, land use and disturbances to understand what explains the distribution of forests. Forests were associated with areas of steeper slopes, watercourses and higher surface runoff, in deeper soils with higher water availability, along a longitudinal climatic gradient, with less livestock and land-use intensity and higher human presence. We discuss how, in ancient grasslands such as this one, sub-regional geology and local topography can be permanent features that generate spatial heterogeneity in forest cover probability by mediating resource availability and influencing land use and disturbance regimes.
... However, there are still significant gaps in our understanding of the global distribution of biodiversity, especially about the invertebrates and their conservation significance (Kier et al. 2005, Murphy et al. 2016). In addition, there is a conspicuous paucity of knowledge about the biodiversity in savannas (Parr et al. 2014, Murphy et al. 2016. ...
Savannas are recognized as one of the world’s most biodiverse ecosystems. However, these environments have the highest rates of habitat loss due to land use and climate-induced alterations in fire regimes. The combination of these threats, along with knowledge gaps in biodiversity, represents formidable challenges to conservation efforts in these regions. Dung beetles, vital for comprehending the impact of land use on savannas, have yet to undergo comprehensive study. To address this gap, we conducted a systematic review of the current state of knowledge regarding dung beetles distributed in savannas within Neotropical, Afrotropical, and Australasia zoogeographic regions. We describe the encompassing geographical distribution, research topics, studied habitats, and key metrics assessed in existing studies. Our results reveal a pronounced focus on Neotropical savannas highlighting a substantial deficit in dung beetle ecology knowledge within Afro-tropical and Australasian savannas. Most articles focused on savanna grasslands, woodlands, and human-introduced habitats such as pastures. The predominant articles focused on community patterns, habitat replacement, and degradation. Noteworthy metrics included abundance, richness, and species composition. Diversity indexes and functional diversity were also relatively well-explored metrics. However, across all zoogeographic regions, aspects of dung beetle behavior, reproductive biology, and physiology remain inadequately explored. In conclusion, urgent research efforts are imperative, emphasizing the need for comprehensive metrics, including biomass, morphometrics, and ecological functions of dung beetles, to advance our understanding of their significance and roles within savannas.
... Termites are a relevant component of tropical biome ecology , constituting the majority of animal biomass in savannas, including the Cerrado (Redford, 1984), the largest, richest, and most threatened Neotropical Savanna (Parr et al., 2014). Termites play pivotal roles in nutrient cycling dynamics (D'Angioli et al., 2024) and soil formation processes (Crowther et al., 2019). ...
Termites are key components of tropical ecosystems, particularly in the Cerrado biome, where they dominate animal biomass and play crucial roles in nutrient cycling and soil formation. Their abundance and nutritional value make them primary food sources for various Cerrado animals, influencing predator diversity and several ecological interactions. Additionally, termite mounds serve as essential shelters for a wide range of fauna, aiding in thermoregulation and providing refuge from harsh environmental conditions, including wildfires. In this scenario, termitaria survival, diversity, and availability have several effects on the Cerrado fauna ecology. We present novel insights into the interaction between Actinobolus beetles and epigeous termite mounds in the Cerrado. Our field observations revealed Actinobolus beetles utilizing termite mounds for feeding and reproduction in several localities of Cerrado. These beetles access the inner portion of the termitaria, where the colony nest is located and protected by the termitaria's harder external layer and their larvae consume the termite nest structure. Actinobolus attack leads to partial or complete destruction of the colony and the creation of large hollows inside the mounds, causing deep changes in its structure. Despite the defensive mechanisms of termites, Actinobolus larvae thrive within the nest and likely ingest termites' eggs, nym-phae and adults. Furthermore, we found that the Actinobolus capsule are made of faecal pellets, instead of termitaria debris. We suggest that the interaction between Actinobolus beetles and epigeous termitaria impacts the role of termi-taria in providing microclimate regulation, food and shelter for Cerrado fauna, likely having poorly understood effects on the conservation and management of Cerrado ecosystems. K E Y W O R D S Central Brazil, fire, microclimate, shelter, termite mounds, termitophilous Resumo Os cupins são componentes-chave dos ecossistemas tropicais, especialmente no bioma Cerrado, onde dominam a biomassa animal e desempenham papéis cruciais na ciclagem de nutrientes e na formação do solo. Sua abundância e valor nutricional os tornam fontes primárias de alimento para diversos animais do Cerrado, influenciando a diversidade de predadores e diversas interações ecológicas. Além disso, os cupinzeiros são abrigos essenciais para diversos animais, auxiliando na termorregulação e proporcionando refúgio contra condições ambientais adversas, incluindo incêndios florestais. Nesse cenário, a sobrevivência, a diversidade e a disponibilidade dos cupins têm vários efeitos na ecologia da fauna do Cerrado. Apresentamos novos observações sobre a interação entre besouros Actinobolus e cupinzeiros epígeos no Cerrado. Besouros do gênero Actinobolus utilizam 2 of 8 | de LIMA and BRANDÃO
... Our research underscores the subtle variation in plant-soil diversity within Florida's subtropical grasslands that is characteristic of the broader region (Wheeler and Peet 2016). Such localized diversity and endemism deserve our conservation and research attention, especially given numerous calls to better understand subtropical and old-growth grassland ecology (Parr et al. 2014;Nerlekar and Veldman 2020). Table A2. ...
... Cerrado is an important tropical grassy phytogeographic domain that harbors a unique biodiversity and provides significant ecological services to humankind (Bond and Parr, 2010;Overbeck et al., 2015;Parr et al., 2014). Despite its importance, this ecosystem have been neglected regarding conservation public policies and are facing considerable threats due to human disturbance (Klink and Machado, 2005;Overbeck et al., 2015). ...
... C4 species are more widespread, dominating the warmer and drier areas of Cabo Verde. This agrees with the usual worldwide ecological pattern: C4 species tolerate lower water availability and higher temperatures (preferring tropical regions), whereas C3 species are most efficient under high water availability and are particularly welladapted to mild temperatures (more common in temperate regions) (Parr et al., 2014;Pearcy & Ehleringer, 1984;Woodward et al., 2004). The C4 pathway allows a higher water-use efficiency (Pearcy & Ehleringer, 1984), providing a competitive advantage in more arid environments (Edwards & Still, 2008;Simpson et al., 2020). ...
Grasses are one of the most successful and dispersed plant families worldwide and their environmental and economic values are widely acknowledged. They dominate the landscape of Cabo Verde, the southernmost and driest archipelago of Macaronesia, and are relevant natural resources for local populations, but a comprehensive evaluation of their distribution patterns is still lacking. In this study, we aim to evaluate the potential effects of climate change using the long-term data concerning grass distribution in Cabo Verde and the widely recognized climatic variability of this archipelago, which entails a huge irregularity in spatial and temporal rainfall. We identified two contrasting climatic periods (wet, from 1929 to 1968, and dry, from 1969 to 2007) and gathered all the information available from the bibliography, herbaria, and fieldwork concerning spontaneous grass species recorded in Cabo Verde during those two periods, which amounted to 107 taxa. This information was then used to disclose the patterns of grass diversity as related to climatic and topographic variables (altitude and windward vs. leeward aspects). Different altitudinal shifts in the distribution patterns of grass species assemblages and an assemblage specific to the wet period were revealed by comparing the two climatic periods. The role of exposure in delimiting the altitudinal distribution of the various assemblages was highlighted; the trade winds clearly determine the distribution of grass assemblages. We detected shifts in the distribution of grass assemblages according to the climatic periods (related to the macroclimate) and local topographic factors (associated with mesoclimates). Also, functional traits (i.e., annuals vs. perennials, C3 vs. C4 grasses, and tropical vs. temperate species) were found to vary between wet and dry periods, as well as with altitude and with slope aspect. Understanding species distributions and the role of the climatic variability of Cabo Verde is crucial to predicting how climate change will affect them and thus to support effective management and conservation actions.
... Most current studies focused on the impact of fires on forests (Armenteras et al., 2021;Le Page et al., 2017;Liu et al., 2019). However, savannahs, grasslands, and other ecosystems in South America also play important roles and are subjected to shifting fire regimes (Kumar et al., 2022;Parr et al., 2014). The large-scale effects of altered fire frequency on them are still not well understood. ...
Fire events in South America are becoming more extensive and frequent as climate extremes and human pressures increase, and even repeatedly occurring in some areas within decades. However, the relationship between recurring fires and vegetation dynamics remains unclear. Here, we extracted the number of fire occurrences using burned area satellite product and analysed the relationship between recurring fires and vegetation dynamics with remote sensing land use and vegetation index datasets in South America. We show that approximately 1.39 × 10 ⁶ km ² of burnt area has experienced recurring fires during 2001–2020. More than half of burnt area of recurring fires occurred in savannahs with remaining burnt area in grasslands, forests and croplands. Although forests tended to be less susceptible to recurring fires among all vegetation types, their coverage loss with recurring fires was the greatest. The greater proportion of forest conversion to croplands concurred with more recurring fires. Conversely, the coverage of croplands and grasslands gained the most with recurring fires. In the areas without vegetation conversion, more frequent recurring fires further suppressed canopy greenness and density, even in fire‐adapted savannahs and grasslands. Our results suggest that recurring fires and land use change are generally coincident, reflecting the intense pressure of human activities on natural vegetation in South America. Thus, coordinated efforts on vegetation conservation and sustainable management of human‐induced burning in the region are urgently needed.
... Globally, grassland bird conservation is constrained by a critical lack of research on grassland ecology and insufficient knowledge of the natural history and habitat associations of many grassland bird species [2,9,10]. This is especially true in the Neotropics, the exception of one study that showed that the Cock-tailed Tyrant and Black-masked Finch may be intolerant to grazing [42]. ...
Grassland birds are globally imperiled. Those of endemic Neotropical savannas may be particularly threatened as knowledge of the ecology of many species is lacking, restricting our ability to take decisive conservation action. During the dry (non-breeding) season of 2010, we studied the population size, distribution, and habitat associations of the Cock-tailed Tyrant (Alectrurus tricolor), Black-masked Finch (Coryphaspiza melanotis), and Wedge-tailed Grass-finch (Emberiziodes herbicola) across a disturbance-mediated savanna–grassland gradient in Beni, Bolivia. We used distance sampling and surveyed structural and resource-specific habitat features at plots where birds were present versus random locations. Occupancy models identified fine-scale habitat associations. Cock-tailed Tyrant (7.1 ind./km2) specialized on open habitats in areas expected to be heavily inundated in the wet season, avoided trees, and selected tall grassy swards. Black-masked Finch (25.1 ind./km2) occurred across the gradient, associating with tall, forb-rich swards, sparse shrubs, and low levels of fruiting and seeding vegetation. Wedge-tailed Grass-finch (27.9 ind./km2) also occurred across the gradient, particularly associated with tall, forb-rich swards, abundant seeding grasses, and sparse shrubs. Our results offer the first quantitative abundance estimates for these species in Beni, provide vital baselines for future monitoring, and improve knowledge of the ecology and conservation management needs of these species. Importantly, our results suggest that populations of these three grassland birds may be best maintained in heterogenous, mosaic landscapes that can be produced by carefully managed burning and grazing. Further research in the breeding season would facilitate making stronger, more specific management recommendations.
... However, this study was conducted in forests with contrasting levels of disturbance and only used seeds, so it is not known whether compensatory responses would have been observed with other types of small food resource or in less disturbed habitats. That these types of manipulative experiments have rarely been carried out is concerning because these ecosystems, particularly tropical ones, are undergoing rapid environmental change and biodiversity loss (Parr et al., 2014). It is critical that we evaluate the vulnerability of functions such as scavenging to changes in biodiversity, particularly in rapidly changing ecosystems (Barlow et al., 2018). ...
Functional redundancy, the potential for the functional role of one species to be fulfilled by another, is a key determinant of ecosystem viability. Scavenging transfers huge amount of energy through ecosystems and is, therefore, crucial for ecosystem viability and healthy ecosystem functioning. Despite this, relatively few studies have examined functional redundancy in scavenger communities. Moreover, the results of these studies are mixed and confined to a very limited range of habitat types and taxonomic groups.
This study attempts to address this knowledge gap by conducting a field experiment in an undisturbed natural environment assessing functional roles and redundancy in vertebrate and invertebrate scavenging communities in a South African savanna.
We used a large‐scale field experiment to suppress ants in four 1 ha plots in a South African savanna and paired each with a control plot. We distributed three types of small food bait: carbohydrate, protein and seed, across the plots and excluded vertebrates from half the baits using cages. Using this combination of ant suppression and vertebrate exclusion, allowed us explore the contribution of non‐ant invertebrates, ants and vertebrates in scavenging and also to determine whether either ants or vertebrates were able to compensate for the loss of one another.
In this study, we found the invertebrate community carried out a larger proportion of overall scavenging services than vertebrates. Moreover, although scavenging was reduced when either invertebrates or vertebrates were absent, the presence of invertebrates better mitigated the functional loss of vertebrates than did the presence of vertebrates against the functional loss of invertebrates. There is a commonly held assumption that the functional role of vertebrate scavengers exceeds that of invertebrate scavengers; our results suggest that this is not true for small scavenging resources.
Our study highlights the importance of invertebrates for securing healthy ecosystem functioning both now and into the future. We also build upon many previous studies which show that ants can have particularly large effects on ecosystem functioning. Importantly, our study suggests that scavenging in some ecosystems may be partly resilient to changes in the scavenging community, due to the potential for functional compensation by vertebrates and ants.
... Threats to TGB are not only due to different degradation pressures but also because of historical misunderstandings, undervaluation and insufficient knowledge and protection (Parr et al., 2014;Pausas & Bond, 2019;Pilon et al., 2023;Silveira et al., 2022;Tölgyesi et al., 2022). Despite covering nearly 40% of the land (Dinerstein et al., 2017), a restoration policy, science and practice framework for TGB is still in their infancy (Silveira et al., 2022) given that clear definitions of reference ecosystems have emerged only recently (Bond & Parr, 2010;Veldman et al., 2015). ...
Scientists and policymakers are becoming aware of the pressing need to restore tropical grassy biomes (TGB), which are home to unique biodiversity and provide essential ecosystem services to hundreds of millions of people. TGB face increasing threats, including forest‐ and tree‐centric restoration approaches that promote their degradation and we still lack a systematic assessment of where and how TGB restoration research has been done to guide policy and practice.
We synthesized knowledge on field restoration experiments by conducting a systematic literature review to map TGB restoration field studies, examine the association of restoration techniques and degradation sources and investigate the diversity of indicators used to monitor restoration outcomes.
TGB restoration was concentrated at Brazilian and Australian savannas, with large blindspots in Asia, Africa and northern and western South America. Studies were largely context‐dependent, with an inconsistent usage of restoration techniques to different sources of degradation. Less than half of the indicators evaluated were monitored consistently through time, often using a low‐dimensional approach related to ecosystem functioning. Few studies manipulated fire, herbivores and soils, the key drivers for the re‐establishment of TGB dynamics. Unfortunately, many studies lacked negative (degraded ecosystems), positive (reference ecosystems) controls, or both, impairing attempts to robustly determine restoration outcomes.
Our overview of field research on TGB restoration highlights that research needs improvement to refine our ability to assess, plan, implement and monitor restoration. Severe issues with experimental designs and data reporting are identified as barriers to find generality and upscale TGB restoration to meet the goals of the UN Decade on Ecosystem Restoration.
Synthesis and applications. Our synthesis calls for enhanced field experiments, transparent data reporting and quantitative syntheses to guide large‐scale TGB restoration. The overall lack of knowledge on improving resilience and measuring outcomes hampers meaningful comparisons between studies and hinders synthetic views essential for determining appropriate restoration techniques for different degradation sources and suitable monitoring indicators. To overcome the scarcity of reliable and transparent data supporting TGB restoration, we propose a simple checklist for minimum research reporting information and more complete multilingual standardized guidelines.
... These broad habitat types have been highlighted in previous research as conservation priorities. For example, Tropical Dry Forests and Tropical Grassland, Savanna & Shrubland are considered threatened and classified as priority habitats due to diverse microhabitats, endemism, as well as their role in global terrestrial net primary productivity and carbon storage (Parr et al., 2014;Pinedo-Escatel et al., 2021;Salinas et al., 2021;Wan and Wang, 2023;Wilson and Peter, 1988). However, while these general classifications are useful starting points, this study goes further by identifying specific vegetation types within these broad categories that require particular attention. ...
The Americas contain highly biodiverse yet vulnerable ecosystems, with many threatened species inadequately protected. Finer-scale, localized habitat assessments are crucial for effective conservation planning, but continental-scale high-resolution vegetation maps remain limited. This study addresses this gap by identifying critical vegetation types across the Americas using the standardized framework of the International Vegetation Classification (IVC) system at the macrogroup level, representing the finest vegetation classification available across the region, as well as the highest-resolution Area of Habitat (AOH) maps currently available for birds and mammals. By combining these high-resolution IVC macrogroup maps with detailed AOH maps, we highlight at-risk vegetation types based on 1) threatened and macrogroup-associated species (species that have at least 50% of their AOH in one macrogroup), 2) current protection levels, and 3) projected threats from land use changes, and 4) develop a conservation value index (CVI) that accounts for all these factors. The results highlighted the remarkable diversity of high conservation value macrogroups across the Americas, emphasizing their significance in regions such as the Andes, montane Mesoamerica, the Caribbean, Brazil's Cerrado, and the Atlantic Forest. Among the highest-scoring macrogroups, the Northern Andean Montane & Upper Montane Humid Forest emerged as critically important, harboring a high number of threatened and macrogroup-associated species. Other macrogroups of immediate conservation concern include the Brazilian Atlantic Montane Humid Forest, Pacific Mesoamerican Seasonal Dry Forest, Caribbean Lowland Humid Forest, and Central Midwest Oak Forest, Woodland and Savanna. However, the study revealed that nearly three-quarters of the over 300 macrogroups in the Americas fall below the global target of 30% protection. Notably, a fifth of all species were macrogroup-associated species, including over 40% of threatened species. Our findings emphasize the need for targeted conservation strategies that consider finer-scale habitat classifications and paired with high-quality species distribution data to guide conservation strategies for biodiversity across the Americas.
... Open biomes are also rich in endemic species and thus have a particularly high conservation value (Murphy et al., 2016), and are associated with almost half of the global biodiversity hotspots (Hopper et al., 2021;Myers et al., 2000). Yet, open biomes are experiencing severe threats (Bardgett et al., 2021;Parr et al., 2014;Strömberg and Staver, 2022), which are also linked to the prevailing, and still persisting paradigm that considers them degraded early stages of forest succession, suitable for conversion to intensive agriculture or afforestation (for an overview, see Veldman et al., 2015;Veldman, 2016). The critical importance for ecosystem functioning, climate change mitigation, and biodiversity conservation of open biomes has been historically ignored despite repeated calls by the scientific community (e.g., Bond, 2019;Buisson et al., 2022;Veldman et al., 2015). ...
Open biomes such as grasslands, savannas, shrublands are associated with many global biodiversity hotspots, and cover ∼60% of land globally. Yet, extensive and increasing anthropogenic activities threaten their functioning and biodiversity. Here, we argue that, in open biomes, researchers and stakeholders (e.g., policy-makers, practitioners) should more comprehensively acknowledge that more than half of a plant’s biomass is typically located belowground. Not only fine roots but different belowground coarse organs of plants (e.g., thick roots, rhizomes) play key ecosystem functions that have been largely neglected in basic and applied ecology. By more accurately accounting for the distribution of these organs along ecological gradients, their biomass turnover and decomposition rate, we would improve estimates of carbon cycling (core in climate change mitigation policies) as well as ameliorating conservation efforts focused on open biomes worldwide.
... Lightningcaused wildfire is an integral component of savanna ecosystems, occurring because of the abundance of a flammable fuel load and a relatively long dry season [17]. Fire and the frequency of fire are important agents of disturbance which help control the distribution and composition of the trees, shrubs, and herbaceous components of savannas [18], for example, through the grass-fire cycle [19]. However, the socio-economic impacts of fire can be substantial, including livestock death and the destruction of field crops, firewood, thatch grass, and trees [20]. ...
Zimbabwe’s woodland and forests have experienced substantial change over the last two decades. In this study, our objective was to assess national-scale spatio-temporal changes in tree loss, wildfire, and population growth since 2000 using global data. Our results showed rates of tree loss were highest in the urbanized Harare and Bulawayo provinces between 2000–2004, followed by Masvingo and Manicaland provinces. We found agricultural versus non-agricultural land type classes had higher tree loss, with the highest rates in small resettlement farms (‘A1’ farms, averaging 5 ha in size) between 2000–2008. The findings from our analysis of wildfire showed burning peaked in 2010, impacting 12% of the country. In the peak fire years of 2008–2012, 30% of A2 self-contained resettlement farms (‘A2’ farms, averaging 318 ha in size) burned, along with 19% of A1 resettlement farms. Analysis of global population data showed increases across all provinces, particularly in large-scale commercial farming areas, with gradual increases seen in A1 and A2 farms. Understanding the trends over two decades and the patterns in three key pressures—tree loss, population change, and fire—provides an important contribution to help guide regional assistance efforts in Zimbabwe.
... Because they occur across such a wide range of environmental and land use conditions, savannas can vary considerably in terms of tree cover and species composition. Savannas are threatened by a range of issues, including agricultural expansion, elevated atmospheric CO 2 , invasive species, altered fire regimes, deforestation, and afforestation (Parr et al., 2014;. ...
Strategies for equitably managing savannas are urgently needed as these ecosystems undergo significant social and ecological changes that threaten their sustainability and the livelihoods of those that depend upon them. Using snowball sampling, we interviewed 28 key informants in Velingara, Senegal, to quantify the relative socio-cultural importance of savanna species and understand the drivers and impacts of environmental change as experienced by local people. We identified 43 species of particularly high socio-cultural importance, only eight of which are considered highly important in other areas of Senegal and West Africa, which underscores the need for local-scale ethnobotanical studies of how livelihoods and cultural values intersect with biophysical changes in West African savannas. Respondents identified a drying trend associated with declines in tree and grass biodiversity. Biodiversity loss was further associated with changing market forces, fire regimes, and an invasive herb. We situate our results within a broader West African ethnobotanical context, and propose four guiding principles to facilitate equitable and sustainable management of Sudano-Guinean savanna: (1) Monitor migration as an adaptation strategy for both humans and plants, (2) Pursue a biocultural approach to savanna restoration, (3) Co-create collaborative strategies for governing the commons, and (4) Develop international, market, and policy-based strategies for curbing local timber harvesting.
... Further, research addressing effects of land-use intensification on multiple ecosystem services and their interactions (i.e., tradeoffs and synergies) in grasslands has predominantly focused on temperate or semiarid regions 9 . Subtropical grasslands, with their unique and often humid climate and distinctive biophysical characteristics and management practices, have received far less attention but are facing acute threats from ongoing degradation 29 . Such knowledge is urgently needed, given that~50% of the global population will reside in the subtropics and tropics by 2050 30 , potentially leading to more intensified land uses and other anthropogenic modifications in this biogeographic region. ...
Sustainable agricultural intensification could improve ecosystem service multifunctionality, yet empirical evidence remains tenuous, especially regarding consequences for spatially coupled ecosystems connected by flows across ecosystem boundaries (i.e., metaecosystems). Here we aim to understand the effects of land-use intensification on multiple ecosystem services of spatially connected grasslands and wetlands, where management practices were applied to grasslands but not directly imposed to wetlands. We synthesize long-term datasets encompassing 53 physical, chemical, and biological indicators, comprising >11,000 field measurements. Our results reveal that intensification promotes high-quality forage and livestock production in both grasslands and wetlands, but at the expense of water quality regulation, methane mitigation, non-native species invasion resistance, and biodiversity. Land-use intensification weakens relationships among ecosystem services. The effects on grasslands cascade to alter multifunctionality of embedded natural wetlands within the metaecosystems to a similar extent. These results highlight the importance of considering spatial flows of resources and organisms when studying land-use intensification effects on metaecosystems as well as when designing grassland and wetland management practices to improve landscape multifunctionality.
... As a result, regions such as the South American Chaco and Chiquitania, or the Indochina dry woodlands are global deforestation hotspots (Buchadas et al., 2022). Despite these pressures, tropical and subtropical dry woodlands have received less attention than tropical rainforests by the scientific community, policymakers and the public at large (Parr et al., 2014;Pendrill et al., 2022). ...
... Foundational insect surveys are critical for establishing insect baseline data, providing data that can be used to assess changes in insect biodiversity and distributions across time and geographic space. African ant diversity studies have more commonly focused on forested areas (Belshaw & Bolton, 1994;Deblauwe & Dekoninck, 2007;Fisher & Robertson, 2002;Fotso et al., 2015;Robertson, 2002;Schulz & Wagner, 2002) and anthropogenic habitats (Fisher & Robertson, 2002;Fotso et al., 2015;Jackson, 1984;Kone et al., 2012Kone et al., , 2014Majer, 1972;Majer, 1976;Perfecto & Vandermeer, 2013) than on native open-canopy habitats (but see e.g., Purdon et al., 2019;Mauda et al., 2018;Yeo et al., 2011;Parr et al., 2014;Tshiguvho et al., 1999). In particular, the ant biodiversity of woodland savannah in West Africa is poorly known, with the exception of a few studies from Côte d'Ivoire (Yeo et al., 2011;Yeo et al., 2017). ...
Community‐based conservation can play an important role in preserving biodiversity, but it is unclear whether such benefits extend to invertebrate communities; in particular, baseline data for insect communities is lacking to assess efficacy of conservation efforts. Here we evaluate ant assemblages across three habitats, protected within the Wechiau Community Hippo Sanctuary (WCHS) in the Upper West Region of Ghana. We compare relative ant species diversity and uniqueness between the sanctuary's Guinea savannah, riparian forest, and floodplain habitats. Ants were collected with other invertebrates using malaise traps, pitfall traps, and yellow pan traps between 2001 and 2011 multiple times per year. From these data, we compiled a list of ant species found, castes collected, and functional groups, and evaluated the differences in ant diversity among the habitats using accumulation curves, assemblage structure comparison, and Morisita‐Horn indices. We also compared the overall WCHS assemblage to other ant assemblages in Western Africa to gain a clearer understanding of relative diversity and uniqueness. We collected 83 species from seven subfamilies and 44 genera; 14 of the species were previously unrecorded in Ghana, including one ant species new to science. Ant species diversity differed among habitats in assemblage composition but not significantly in species richness. We found that the WCHS ant assemblage was relatively unique, sharing only about 35% of species found in similar Côte d'Ivoire habitats, and 25% of other Ghanaian assemblages. Some species present in the WCHS were not found in any of the other compared assemblages. We conclude that community‐based conservation initiatives like the WCHS may play an important role in conserving the biodiversity of ants.
... The historic extent of the world's tropical savannas once covered nearly 12 million km 2 , but only about 20% of this extent remains in good condition today, and remnants are often fragmented (Woinarski et al., 2007). Inappropriate savanna fire regimes contribute to habitat alteration, degradation, fragmentation, and loss of biodiversity (Durigan & Ratter, 2016;Parr et al., 2014;R. J. A. Williams, Woinarski, & Andersen, 2003;Woinarski et al., 2007). ...
Fire‐dependent savanna provides key habitat for butterflies globally, but we know little about how fire regimes, including fire frequency and season, affect them. These impacts are likely to be primarily indirect, through changes in overall habitat structure, the abundance of larval host plants, and/or the provision of nectar resources for adults. We examined the relationships among fire regime, butterfly abundance and diversity, and vegetation structure and floral resources within a long‐term fire experiment near Darwin in the Australian monsoon tropics. We surveyed butterflies and floral resources throughout the 2019–2020 wet season in three replicate plots of each of six experimental treatments that had been operating for 15 years. All plots subject to fire had been burned in the previous dry season. We observed 24 butterfly species and 280 individuals representing all five butterfly families found in Northern Australia. Butterfly abundance was highest under early dry‐season (June) fire regimes (mean = 11.9 individuals per plot survey) compared with a late dry‐season (October) regime (mean = 6.7) and in the long‐term absence of fire (mean = 5.3), and this was correlated with the abundance of floral resources. The distribution of butterflies was also highly associated with floral resources within plots regardless of fire treatment. Butterfly species richness was significantly higher in early dry‐season (mean = 6.8) compared with unburned (mean = 3.3) plots but did not differ between early and late dry‐season (mean = 4.7) plots. Butterfly and floral diversity were similar across all early dry‐season fire treatments regardless of whether they had been burned every 1, 2, 3, or 5 years. Our finding that early dry‐season burning promotes butterfly diversity and abundance by increasing the supply of nectar resources has important implications for biodiversity management more broadly, given that nectar is a critical resource for many animal taxa.
... Afroalpine habitat restoration and protection can combat climate change by sequestering carbon (Ni 2002, Parr et al. 2014, Liu et al. 2020. These approaches can also enhance climate resilience during long drought seasons (Johansson et al. 2018) and reduce greenhouse gas emissions (Dong et al. 2020). ...
Habitat alteration and climate change are important threats to terrestrial biodiversity in the tropics. Endorsing flagship or umbrella species can help conserve sympatric biodiversity, restore degraded ecosystems and achieve United Nations Sustainable Development Goals (UN SDGs). The Ethiopian wolf ( Canis simensis ) is a rare and endemic Ethiopian canid. It is Africa’s most endangered canid species and is restricted to several isolated patches of Afroalpine habitats. While its behavioural ecology and conservation biology have been well studied, studies of the Ethiopian wolf’s significance for the conservation of its habitat and sympatric species are lacking. Here we use geographical range overlap and geospatial modelling to evaluate the importance of the Ethiopian wolf as a flagship and/or umbrella species. We assess whether conservation interventions targeting the Ethiopian wolf could help to restore and protect Afroalpine habitat and conserve sympatric species whilst simultaneously providing a wide range of socioeconomic and environmental benefits. We found that Ethiopian wolves share their range with 73 endemic and/or threatened vertebrate species, 68 of which are Afroalpine ecosystem species, and at least 121 endemic and/or threatened plant species. Ethiopian wolves are taxonomically distinctive and charismatic species classified as Endangered on the International Union for Conservation of Nature (IUCN) Red List. Thus, they meet both the flagship and umbrella species criteria to restore Afroalpine habitats and conserve threatened sympatric species. A conservation strategy protecting and restoring Afroalpine habitat has the potential to contribute to achieving at least five of the 17 UN SDGs. The protection of flagship and umbrella species should be integrated into broader regional biodiversity and habitat conservation.
... En nuestro estudio, los cinco macrogrupos de vegetación críticos principales están categorizados dentro de clasificaciones globales de vegetación conocidas como formaciones, dos niveles por encima de los macrogrupos en la jerarquía IVC. prioritarios debido a la diversidad de microhábitats, endemismos, así como su rol en la productividad primaria neta terrestre global y el almacenamiento de carbono (Parr et al., 2014;Pinedo-Escatel et al., 2021;Salinas et al., 2021;Wan y Wang, 2023;Wilson y Peter, 1988). Sin embargo, mientras que estas clasificaciones generales son puntos de partida útiles, este estudio va más allá al identificar tipos de vegetación específicos dentro de estas categorías amplias que requieren atención particular. ...
The Americas contain highly biodiverse yet vulnerable ecosystems, with many threatened species inadequately protected. Finer-scale, localized habitat assessments are crucial for effective conservation planning, but continental-scale high-resolution vegetation maps remain limited. This study addresses this gap by identifying critical vegetation types across the Americas using the standardized framework of the International Vegetation Classification (IVC) system at the macrogroup level, representing the finest vegetation classification available across the region, as well as the highest-resolution Area of Habitat (AOH) maps currently available. By combining these high-resolution IVC macrogroup maps with detailed AOH maps, we highlight at-risk vegetation types based on 1) threatened and macrogroup-associated species (species that have at least 50% of their AOH in one macrogroup), 2) current protection levels, and 3) projected threats from land use changes, and 4) develop a conservation value index (CVI) that accounts for all these factors. The results highlighted the remarkable diversity of high conservation value macrogroups across the Americas, emphasizing their significance in regions such as the Andes, montane Mesoamerica, the Caribbean, Brazil's Cerrado, and the Atlantic Forest. Among the highest-scoring macrogroups, the Northern Andean Montane & Upper Montane Humid Forest emerged as critically important, harboring a high number of threatened and macrogroup-associated species. Other macrogroups of immediate conservation concern include the Brazilian Atlantic Montane Humid Forest, Pacific Mesoamerican Seasonal Dry Forest, Caribbean Lowland Humid Forest, and Central Midwest Oak Forest, Woodland and Savanna. However, the study revealed that nearly three-quarters of the over 300 macrogroups in the Americas fall below the global target of 30% protection. Notably, a fifth of all species were macrogroup-associated species, including over 40% of threatened species. Our findings emphasize the need for targeted conservation strategies that consider finer-scale habitat classifications and paired with high-quality species distribution data to guide conservation strategies for biodiversity across the Americas.
... As per agricultural perspectives, there are three major types of grasslands including natural, seminatural, and improved grasslands [9,10]. Natural grasslands basically form the grassland biomes and these were created by practices related to climate, fire, and wildlife grazing [11], but are also used by livestock. In comparison to natural, seminatural grasslands are formed through human management, and for their maintenance, it needs livestock grazing or hay-cutting [12]. ...
Grasslands (also known as savanna, prairie, steppe, and pampas) are natural or seminatural areas encompassing vegetation belonging to the family Poaceae as the most dominant vegetation, while, sedges and rushes may also constitute a minor proportion. These provide numerous natural products such as food feed medicinal raw material, and honey along with nonproduct-based ecosystem services. Grasslands in lowlands and mountains either in natural form or developed landscape can provide an added value in terms of ecotourism opportunities owing to having huge esthetic and recreational potential compared to uniform agricultural areas. Grasslands characterized by high species and habitat diversity-based ecotourism are nature-based tourism whereby people visit natural or developed areas for recreation, sight-seeing, permitted and controlled hunting, on-site purchase of organic products, etc., and are usually managed by adopting sustainable practices. Ecotourism generates multifaceted economic advantages for local communities such as direct sale of products to tourists. However, ecotourism may also have a variety of negative impacts when the tourists’ number multiplies which leads to overuse of resources. The most pronounced challenges confronted to the development of grasslands for ecotourism include lack of community cooperation, careless herders, need of hefty investment, and absence of trained human capital along with climate change and loss of biodiversity.
... These carbon gains encompass both the growth of mature vegetation and wooded areas re-growing following disturbance, but do not include growth in non-wooded areas (<10 Mg C ha −1 ), or nonwooded to wooded transitions, due to additional uncertainties on change detection in low AGC areas. Whilst these carbon benefits may help address the climate change mitigation agenda, it is important to acknowledge that increasing woody biomass in more open ecosystems can be associated with a loss of biodiversity 40 , and in parts of our study region, may directly conflict with biodiversity management goals. There is likely a dichotomy between the wetter regions of the study (the Miombo woodlands) where increasing woody cover is rarely perceived as a biodiversity threat, and associated with higher faunal and floral diversity 41,42 , and the more open arid ecosystems where it is a key concern of land managers 43 . ...
Protected areas are increasingly promoted for their capacity to sequester carbon, alongside biodiversity benefits. However, we have limited understanding of whether they are effective at reducing deforestation and degradation, or promoting vegetation growth, and the impact that this has on changes to aboveground woody carbon stocks. Here we present a new satellite radar-based map of vegetation carbon change across southern Africa’s woodlands and combine this with a matching approach to assess the effect of protected areas on carbon dynamics. We show that protection has a positive effect on aboveground carbon, with stocks increasing faster in protected areas (+0.53% per year) compared to comparable lands not under protection (+0.08% per year). The positive effect of protection reflects lower rates of deforestation (−39%) and degradation (−25%), as well as a greater prevalence of vegetation growth (+12%) inside protected lands. Areas under strict protection had similar outcomes to other types of protection after controlling for differences in location, with effect scores instead varying more by country, and the level of threat. These results highlight the potential for protected areas to sequester aboveground carbon, although we caution that in some areas this may have negative impacts on biodiversity, and human wellbeing.
... Nevertheless, the proliferation of natural and human-induced degradation such as grass sward removal and climate change jeopardises the services that the savannah grasslands provide [4]. Degraded savannah grasslands tend to sequester and store carbon at a slower rate than normal [5], a process which is being intensified by climate change. ...
Recently, the move from cost-tied to open-access data has led to the mushrooming of research in pursuit of algorithms for estimating the aboveground grass biomass (AGGB). Nevertheless, a comprehensive synthesis or direction on the milestones achieved or an overview of how these models perform is lacking. This study synthesises the research from decades of experiments in order to point researchers in the direction of what was achieved, the challenges faced, as well as how the models perform. A pool of findings from 108 remote sensing-based AGGB studies published from 1972 to 2020 show that about 19% of the remote sensing-based algorithms were tested in the savannah grasslands. An uneven annual publication yield was observed with approximately 36% of the research output from Asia, whereas countries in the global south yielded few publications (<10%). Optical sensors, particularly MODIS, remain a major source of satellite data for AGGB studies, whilst studies in the global south rarely use active sensors such as Sentinel-1. Optical data tend to produce low regression accuracies that are highly inconsistent across the studies compared to radar. The vegetation indices, particularly the Normalised Difference Vegetation Index (NDVI), remain as the most frequently used predictor variable. The predictor variables such as the sward height, red edge position and backscatter coefficients produced consistent accuracies. Deciding on the optimal algorithm for estimating the AGGB is daunting due to the lack of overlap in the grassland type, location, sensor types, and predictor variables, signalling the need for standardised remote sensing techniques, including data collection methods to ensure the transferability of remote sensing-based AGGB models across multiple locations.
... The copyright holder for this preprint this version posted https://doi.org/10.1101.10.03.560737 doi: bioRxiv preprint (Bond, 2019. Loss of open ecosystem habitats supersedes that of tropical rainforest biomes (Parr et al., 2014;Veldman et al., 2015). Often considered wastelands, these open ecosystems harbour rich diversity, which can be vulnerable to conversion to different land uses. ...
With agricultural demands increasing globally, determining the nature of impacts of different forms of agriculture on biodiversity, especially for threatened vertebrates and habitats, is critical to inform land management. We determined the impacts of converting rock outcrops (a habitat more threatened than rainforests) to orchards and paddy on anurans in the Western Ghats biodiversity hotspot. We sampled 50 belt transects four times across four sites during the rainy season and recorded information on amphibians and their microhabitats. We determined community-level responses using Hill numbers, beta-diversity measures, and non-metric multidimensional scaling, and species-level responses using joint species distribution modelling. Converting rock outcrops to paddy and orchards significantly altered microhabitat availability. Conversion to paddy mostly had community-level impacts, i.e., lowered species richness and more nested communities, whereas conversion to orchards mostly had species-level impacts, i.e., lowered species occurrence, highlighting the differential impacts of different forms of agriculture on amphibians and the need to determine impacts of land-use change on communities and species concurrently. We show that large rock pools are critical microhabitats for anurans as they serve as a refuge and protect anurans from desiccation during dry spells, which may be prolonged by climate change. Since rock outcrop habitats in low elevations are rapidly being converted to orchards, efforts are needed to conserve them in partnership with local communities, the custodians of these habitats. Our findings demonstrate that different forms of agriculture can have divergent impacts on biodiversity, and determining their impacts may require assessments at multiple scales, from species to communities.
... However, grasslands across the world are at risk from deterioration due to human activity and may also be harmed by management practices. Investigating how environmental conditions impact the functioning of different grasslands in the context of climate change is therefore crucial 13 .Savannahs, other dryland ecosystems, and tropical and subtropical grasslands cover a large portion of the globe and are vital to sustaining human lifestyles 14 .It is also well acknowledged that Phosphorus is a limiting factor for terrestrial ecosystem production 15 .The primary productivity, nutrient availability, and plant community structure of grassland ecosystems are all in uenced by the phosphorus (P) cycle 16 . Owing to its poor solubility and xation into locked forms in soil, P has played a limiting factor role in ecosystem 17 . ...
Dust particles make up almost all of the atmospheric phosphorus, which accounts for 82% of the total phosphorus in the world. Phosphorus (P) is an important nutrient for terrestrial ecosystems, playing a critical role in influencing primary productivity and hence ecosystem dynamics. The deposition of airborne dust, particularly from arid and semi-arid regions, has been recognized as a significant source of phosphorus input in distant ecosystems. The study area, the Banni Plains, is a semi-arid ecosystem with a unique geological history, that has suffered from degradation due to varied natural and anthropogenic reasons. It is located in arid tract of western India (23º 19' to 23 º 52' N latitude and 68 º 56' to 70 º 32' E longitude).Soil samples were collected from 10*10 km grid locations in the grassland before, after 48 hours, and 20 days after a cyclonic storm, Biporjoy, which hit the region in June, 2023. Statistical analyses (Shapiro-Wilk normality and Kruskalwallis H test) were performed on the data to assess the differences in phosphorus concentrations among the phases. To examine the long-range transport of dust-borne phosphorus and its subsequent deposition in the target grassland, we employed an interdisciplinary approach that integrated satellite imagery and ground-based measurements. Spatial and temporal variations in dust emissions were assessed using satellite remote sensing data, while ground truthing was done for phosphorus content analysis using standard protocols. The aerosol data from MERRA-2 for the past 40 years were used to examine the relationship between aerosol concentrations and wind direction and speed. Our findings reveal that the Middle East, North Africa, and Thar Deserts significantly contribute to the phosphorus deposition in the target grassland during specific seasons. The SW cyclone ‘Biporjoy’ that followed the same track of aerosols loading (MENA) had a landfall on this zone (June 16, 2023) affected the P depositional patterns. The pre cyclone, post cyclone and 20 DAC (Days after Cyclone), had AP values 20.15, 20.54 and 24.06 respectively. However, TP values were 45.81 ± SE = 1.73, 60.95 ± SE = 1.39 and 61.98 ± SE = 1.40 respectively. The highest TP values was in phase 3 (20 DAC phase) 61.89 ± SE = 1.40. Dust storms and other atmospheric circulation patterns were found to play a pivotal role in facilitating the long-range transport of phosphorus-laden dust particles from these source regions to the target grassland. Ultimately, our research contributes to the broader understanding of global nutrient cycling and land-air interactions, enabling informed decision-making for the conservation and sustainable management of terrestrial ecosystems.
... This ecoregion has a markedly seasonal climate (May-September dry season) and comprises a mosaic of vegetation types spanning from grasslands to closed savannas (Ribeiro & Walter, 2008). As for other tropical grassy biomes, fire structures these communities and maintains the open ecosystems where sun-loving species thrive (Moreira, 2000;Parr et al., 2014). In fact, the majority of the Cerrado species are found in the shade-intolerant ground layer and, consequently, prolonged fire exclusion can result in a loss of biodiversity and ecosystem functioning due to woody encroachment (Abreu et al., 2017;Durigan & Ratter, 2016). ...
The relation of fire with the reproductive process of species from tropical grasslands and savannas has long been investigated. Post‐fire flowering is well documented in the Cerrado, but fire‐mediated fruit opening and seed dispersal has rarely been described, with very few historical records being known. Even less is known about the effects of different fire seasons on species reproduction. Here, we describe the fire‐stimulated fruit opening of Jacaranda ulei , an endemic Cerrado shrub with medical importance to traditional communities. We show that fruits opened within 2 weeks after an early dry season fire, but there were almost no viable seeds as fruits were still immature when burned. When put together with the known records for other species, dry dehiscent fruits and anemochory arise as common traits that favour fire‐mediated fruit opening. As these are common attributes in the Cerrado, it is possible that several other species also have fire‐stimulated seed dispersal but remain vastly unnoticed and underreported in the literature. Additionally, the peak reproductive effort of these species coincides with the period of prescribed burns of the Integrated Fire Management Program and, consequently, several species could also have their reproductive cycle interrupted to disperse immature seeds. We hope our note encourages further studies on the fire‐mediated fruit opening and seed dispersal of Cerrado species, particularly in relation to fire season and seed quality.
... Once pioneer species colonize an empty land, later successional phase TRF tree species, which are more shade tolerant, can easily become established (Ratnam et al. 2011;Hoffmann et al. 2012). Furthermore, forest species reduce the likelihood of fire ocurrence and spread of fires as their large canopies cast more shade, reducing herbaceous growth, increasing humidity, and reducing wind speed, which reduces fire occurrence (Ratnam et al. 2011;Hoffmann et al. 2012;Parr et al. 2014). However, most TRF (Aide et al. 2000;Ashton et al. 2014;Holl 1999;Lwanga 2003). ...
The factors governing the dynamics of tropical rainforest (TRF) and humid native savannas are little understood. In Mexico, both biomes are critically endangered owing to land-use change. Tropical pine plantations established in such sites might alter the savanna-TRF dynamics helping to elucidate the underlying factors of the vegetation dynamics in lowland humid tropics. This study aims to investigate the role of Pinus caribaea plantations on the savanna-TRF dynamics in the Gulf of Mexico coastal plain in areas where both biomes are close to one another. Such plantations were established in areas previously occupied by savannas and close to TRF and savanna fragments. Due to unusual circumstances, the plantations remained virtually unmanaged after being planted. We found that after 28–33 years of growth, the understory of pine plantations was similar to that of the TRF in tree species composition, species richness, stem density, and basal area. Pine trees cannot become established under the canopy of TRF, savanna trees, and pine plantations. The understory of savanna trees is unsuitable for establishing most tree species, including savanna trees. Pinus caribaea can alter the TRF-savanna dynamics by facilitating the establishment of TRF species in their understory in areas occupied by savannas, probably due to a combination of properties of both savanna (e.g., fre tolerance) and pioneer TRF (e.g., fast-growing rates) tree species. Thus, our results suggest that exotic pine plantations could be promising tools for TRF regeneration and suppressing savanna regeneration, thus creating a dilemma on what to preserve and restore.
... Aussi, l'étendue spatiale de la biodiversité de ces biomes est menacée par le changement climatique (Higgins et Scheiter, 2012). Malgré ce haut niveau de vulnérabilité, les efforts de conservation sont encore entravés par un manque général de reconnaissance de leur valeur (Parr et al., 2014). Ainsi, le pourcentage de protection de ce biome est inférieur à celui de tous les autres biomes (Hoekstra et al., 2005). ...
L’Afrique de l’Ouest subsaharienne a un cadre physionomique privilégié pour la conservation des Poaceae (Gramineae). Cependant, la détermination des centres de diversité spécifique des Poaceae a été très peu abordée dans les travaux scientifiques. La présente étude avait pour objectif de cartographier les centres de diversité des Poaceae en Afrique de l’Ouest. Elle a donc nécessité la collecte de données d’occurrence sur GBIF et dans le Parc national de la Comoé. Au total, 134127 spécimens de Poaceae concernant l’Afrique de l’Ouest, regroupé en 116 genres et 402 espèces ont été considérés. La zone d’étude a été subdivisée en 506 mailles suivant une résolution spatiale d’une maille de 1.5 x1.5 de côté pour analyser la distribution spatiale de la richesse spécifique. Les résultats montrent que certaines zones comme le nord du Burkina Faso ont été bien échantillonnées par contre d’autres comme le nord-est du Mali ne l’ont pas été. Aussi, la richesse spécifique des différentes grilles croît de la marge sud du Sahara à la latitude 10oN ; puis de la latitude 5oN au niveau du golfe de Guinée à la latitude 10oN. Cette diversité est aussi variable de l’est à l’ouest. La carte de distribution spatiale de l’ensemble des échantillons a mis en évidence les centres de diversités des Poaceae d’Afrique de l’Ouest. English title: Diversity of West African Poaceae, with emphasis on determining centers of diversity for their conservation Sub-Saharan West Africa has a privileged physiognomic framework for the conservation of Poaceae (Gramineae). However, few studies addressing the aspect of determining the centers of specific diversity of this taxon have been published. this present study aimed at maping the centers of diversity of Poaceae in West Africa. The study therefore required the collection of occurrence data on GBIF and in the Comoé National Park in Côte d’Ivoire. In total, 134127 specimens of Poaceae of West Africa, grouped into 116 genera and 402 species were considered. The study area was subdivided into 506 grids according to a spatial resolution of a grid of 1.5 x1.5 on a side to analyze the spatial distribution of species richness. The results show that certain areas such as northern Burkina Faso were well sampled, while others such as northeastern Mali were not. Also, the specific richness of the different grids increases from the southern margin of the Sahara to latitude 10oN; then from latitude 5oN at the level of the Gulf of Guinea to latitude 10oN. This diversity is also variable from east to west. The spatial distribution map of all specimens revealed the centres of diversity of the West Africa Poaceae.
Questions
Fire is an important ecological factor influencing plant communities in many fire‐prone ecosystems. Savannas in the Cerrado are resilient to fire, with plants exhibiting fire‐related traits, allowing them to persist in post‐fire environments. Therefore, excluding fire may result in changes in plant community dynamics, thus affecting their resilience. We investigated the effect of the reintroduction of fire in savannas where fire has been excluded for longer periods (>12 years) on seedling recruitment. We asked the following questions: (i) how does fire affect seed bank germination in sites with different fire histories; and (ii) how did fire exclusion affect species composition of the seed bank?
Location
Estação Ecológica de Itirapina (EEI), Southeastern Brazil.
Methods
Two sites with different fire histories were selected: FE1985 – fire exclusion for more than 30 years, with one fire event in 1985; and FE2009 – fire exclusion for 12 years, with three fire events since 1985, the last one being in 2009. Both areas have low fire frequency, but different times since the last fire. Soil samples were collected before and after prescribed fires to evaluate the effects of fire after longer periods of fire exclusion in the soil seed bank. Using the seedling emergence method, we evaluate the effects of the reintroduction of fire after longer periods of fire exclusion in the soil seed bank.
Results
We found that fire significantly increased the seed bank recruitment at both sites, FE1985 and FE2009 (increase of 16% and 50% in seedling recruitment, respectively), showing that species of the Cerrado responded positively to the fire passage. The reintroduction of fire promoted different effects on seed bank recruitment: shrubs experienced a significant decrease in seedling emergence from the seed bank at FE1985, while their recruitment was not affected at FE2009. Time since last fire appears to influence the seed bank composition, showing a shift in dominance from a grassy community to a woody one.
Conclusions
After fire, more species germinated from the seed bank, showing that direct and indirect effects of fire are affecting seed germination from the seed bank, and its importance on seedling recruitment from the seed bank in the Cerrado.
ABSTRACT
Soil is considered as a potential terrestrial reservoir for atmospheric carbon. The Soil Organic Carbon (SOC) dynamic in relation to different land use change represent a great challenge on which more attention must be focused. Soil plays an important role as dynamic natural body and as a fundamental resource in many ecosystems, particularly in the Mediterranean area which include Spain. The aims of this study are: a) investigate the trends of SOC stocks between 2009 and 2015 since forest are expanding due to abandonment phenomena and b) estimate the capacity of soil properties (e.g., soil texture) to influence C storage in different land uses (e.g., cropland, forest, fruit trees and grassland) using the LUCAS database for two different years (2009 and 2015). Forest and grassland soil show a trend in SOC stock due to the other land use abandonment, while SOC stock decrease in cropland and fruit trees. In 2009, forest land use soil appears to have highest amount of SOC stock of 91.3 Mg C ha-1 with median, 10 and 20 quartiles which could be the result from the increase in SOC (%) over time or increase in SOC (%) result for land abandonment of other land uses. Meanwhile, similar trend occurred in 2015 where forest showed the highest amount of SOC stock of 66.7 Mg C ha-1 with median, 10 and 20 quartiles in 2015, which could be the result of the abandonment of other land uses. The result of this study identifies the difficulty of detecting changes in SOC by direct measurement, which could fall within the uncertainties of the stock measured in the reference year (2009). Soil properties (e.g., soil texture) are the major factor influencing the amount of SOC stored in the different land uses of Spain. The significant increase in the SOC stock measured in forest and grassland soil compare to the lower amount of SOC stock measured in cropland and fruit trees soil result to the hypothesize states that an increase in the SOC stock if forest soil will increase through time is due to the abandonment of the other land uses. Correlation between SOC stock and soil properties in different land use contribute on the investigation on soil capacity in storing SOC for several years. These results could represent precious information in controlling SOC sequestration in the different land use of Spain. However, these results on soil properties are significant in SOC stock estimation and could represent a useful resource to obtain a precise SOC stock at country level and for the future assessment of SOC stock of different land uses in Spain.
Keywords: SOC stock. Soil properties. Cropland soil. Grassland soil. Fruit trees soil. Forest soil.
Woody encroachment (WE) and agricultural expansion are widespread in tropical savannas, where they threaten biodiversity and ecosystem function. In Africa's largest savanna, the miombo woodlands, cropland expansion is expected to cause extensive habitat loss over the next 30 years. Meanwhile, widespread WE is altering the remaining untransformed vegetation. Quantifying the extent of both processes in the Angolan miombo woodlands (~570,000 km ² ) has been challenging due to limited infrastructure, a history of conflict, and widespread landmines. Here, we analyze spectral satellite imagery to investigate the extent of WE and cropland expansion in the Angolan miombo woodlands since 1990. We asses WE using two complementary metrics: multi‐decade canopy greenness trends and conversion from grassland to woodland. We also examine whether WE trends are driven by landscape fragmentation and decreasing fire frequency. We found that from 1990 to 2020, 34.1% of the Angolan miombo woodlands experienced significant WE or was converted to cropland, while open grassy vegetation declined by 62%. WE advanced rapidly even in areas experiencing extraordinarily high burn frequencies and was not adequately explained by changing temperature or precipitation. WE was concentrated far from the agricultural frontier, in remote areas with low population densities. These results challenge the hypothesis that human‐altered fire regimes are the primary driver of WE in mesic savannas. The results will help decision‐makers conserve the miombo woodlands' biodiversity and ecosystem services, by highlighting that strategies to slow habitat loss must address WE and cropland expansion together.
Background
Late dry-season wildfires in sub-Saharan Africa’s savanna-protected areas are intensifying, increasing carbon emissions, and threatening ecosystem functioning. Addressing these challenges requires active local community engagement and support for wildfire policy. Savanna burning emissions abatement schemes first implemented in Northern Australia have been proposed as a community-based fire management strategy for East and Southern Africa’s protected areas to deliver win–win-win climate, social, and biodiversity benefits. Here, we review and critically examine the literature exploring the design and application of savanna burning emissions abatement schemes in this region, characterizing their contextual and implementation challenges.
Results
We show that the application of Northern Australian savanna burning methodologies in East and Southern Africa tends to adopt centrally determined objectives and market-based approaches that prioritize carbon revenue generation at the national level. The exclusive prescription of early-dry season burns in African mesic savannas prone to woody thickening can compromise savanna burning objectives to mitigate late-dry season wildfires and their greenhouse gas emissions in the long-term, as well as present multiple biodiversity trade-offs in the absence of formal metrics monitoring species’ responses to changes in fire regime. These features restrict indigenous participation and leadership in fire management, creating uncertainties over the opportunities for local income generation through carbon trading. Findings suggest that future savanna burning applications will need to address asymmetries between formal institutions and local land governance systems, explicitly acknowledging colonial legacies in institutional arrangements across protected areas and hierarchies in agrarian politics that threaten processes of equitable decentralization in natural resource management.
Conclusion
We argue that the effective transfer of the Northern Australian fire management model is limited by a lack of long-term ecological and emissions data and political and institutional barriers, and is hindered by the region’s recent colonial history, population growth, and consequences of rapid climatic change. To provide a community-based strategy, savanna burning schemes need to establish context-specific legal frameworks and implement Free, Prior, and Informed Consent to safeguard the roles and responsibilities of indigenous and local people and their distribution of carbon benefits.
Some grasslands in ecotones with forests tend to be encroached by woody species, because of changes in climate and land use. Such structural changes in vegetation can be facilitated when the grassland community presents an autochthonous arboreal component, like Butia palms. We aim to identify the responses of taxonomic and functional diversity on grassland community with the occurrence of arborescent/ arboreal species (autochthonous and encroaching) to palm density and grazing intensity. The study was conducted in a Butia odorata palm grove under cattle management, in Southern Brazil. To assess the taxonomic and functional composition we performed ordinations analysis with the vegetational data and using path analysis we assessed the causal relationships between variables of interest. Density of Butia odorata and woody plants were strongly positive related, suggesting a facilitation process in the establishment of arborescent plants on the grassland matrix. The abundance of less palatable plants and grazing pressure were inversely related, indicating a selection process induced by higher grazing intensity. We suggest that the grazing intensity management must be based on the autochthonous tree density, applying higher grazing intensity in areas with higher density of encroaching plants, in addition to maintaining other regions conducive to Butia palm regeneration through fallows.
New burned area datasets and top-down constraints from atmospheric concentration measurements of pyrogenic gases have decreased the large uncertainty in fire emissions estimates. However, significant gaps remain in our understanding of the contribution of deforestation, savanna, forest, agricultural waste, and peat fires to total global fire emissions. Here we used a revised version of the Carnegie-Ames-Stanford-Approach (CASA) biogeochemical model and improved satellite-derived estimates of area burned, fire activity, and plant productivity to calculate fire emissions for the 1997–2009 period on a 0.5° spatial resolution with a monthly time step. For November 2000 onwards, estimates were based on burned area, active fire detections, and plant productivity from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. For the partitioning we focused on the MODIS era. We used burned area estimates based on Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) and Along-Track Scanning Radiometer (ATSR) active fire data prior to MODIS (1997–2000) and Advanced Very High Resolution Radiometer (AVHRR) derived estimates of plant productivity during the same period. Average global fire carbon emissions were 2.0 Pg yr<sup>−1</sup> with significant interannual variability during 1997–2001 (2.8 Pg yr<sup>−1</sup> in 1998 and 1.6 Pg yr<sup>−1</sup> in 2001). Emissions during 2002–2007 were relatively constant (around 2.1 Pg yr<sup>−1</sup>) before declining in 2008 (1.7 Pg yr<sup>−1</sup>) and 2009 (1.5 Pg yr<sup>−1</sup>) partly due to lower deforestation fire emissions in South America and tropical Asia. During 2002–2007, emissions were highly variable from year-to-year in many regions, including in boreal Asia, South America, and Indonesia, but these regional differences cancelled out at a global level. During the MODIS era (2001–2009), most fire carbon emissions were from fires in grasslands and savannas (44%) with smaller contributions from tropical deforestation and degradation fires (20%), woodland fires (mostly confined to the tropics, 16%), forest fires (mostly in the extratropics, 15%), agricultural waste burning (3%), and tropical peat fires (3%). The contribution from agricultural waste fires was likely a lower bound because our approach for measuring burned area could not detect all of these relatively small fires. For reduced trace gases such as CO and CH<sub>4</sub>, deforestation, degradation, and peat fires were more important contributors because of higher emissions of reduced trace gases per unit carbon combusted compared to savanna fires. Carbon emissions from tropical deforestation, degradation, and peatland fires were on average 0.5 Pg C yr<sup>−1</sup>. The carbon emissions from these fires may not be balanced by regrowth following fire. Our results provide the first global assessment of the contribution of different sources to total global fire emissions for the past decade, and supply the community with an improved 13-year fire emissions time series.
Surveying Savannas
Savannas are structurally similar across the three major continents where they occur, leading to the assumption that the factors controlling vegetation structure and function are broadly similar, too. Lehmann et al. (p. 548 ) report the results of an extensive analysis of ground-based tree abundance in savannas, sampled at more than 2000 sites in Africa, Australia, and South America. All savannas, independent of region, shared a common functional property in the way that moisture and fire regulated tree abundance. However, despite qualitative similarity in the moisture–fire–tree-biomass relationships among continents, key quantitative differences exist among the three regions, presumably as a result of unique evolutionary histories and climatic domains.
New burned area datasets and top-down constraints from atmospheric
concentration measurements of pyrogenic gases have decreased the large
uncertainty in fire emissions estimates. However, significant gaps remain in
our understanding of the contribution of deforestation, savanna, forest,
agricultural waste, and peat fires to total global fire emissions. Here we
used a revised version of the Carnegie-Ames-Stanford-Approach (CASA)
biogeochemical model and improved satellite-derived estimates of area
burned, fire activity, and plant productivity to calculate fire emissions
for the 1997–2009 period on a 0.5° spatial resolution with a monthly
time step. For November 2000 onwards, estimates were based on burned area,
active fire detections, and plant productivity from the MODerate resolution
Imaging Spectroradiometer (MODIS) sensor. For the partitioning we focused on
the MODIS era. We used maps of burned area derived from the Tropical Rainfall
Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) and Along-Track
Scanning Radiometer (ATSR) active fire data prior to MODIS (1997–2000) and
estimates of plant productivity derived from Advanced Very High Resolution
Radiometer (AVHRR) observations during the same period. Average global fire
carbon emissions according to this version 3 of the Global Fire Emissions
Database (GFED3) were 2.0 Pg C year−1 with significant interannual
variability during 1997–2001 (2.8 Pg C year−1 in 1998 and
1.6 Pg C year−1 in 2001). Globally, emissions during 2002–2007 were relatively
constant (around 2.1 Pg C year−1) before declining in 2008
(1.7 Pg C year−1) and 2009 (1.5 Pg C year−1) partly due to lower deforestation
fire emissions in South America and tropical Asia. On a regional basis,
emissions were highly variable during 2002–2007 (e.g., boreal Asia, South
America, and Indonesia), but these regional differences canceled out at a
global level. During the MODIS era (2001–2009), most carbon emissions were
from fires in grasslands and savannas (44%) with smaller contributions
from tropical deforestation and degradation fires (20%), woodland fires
(mostly confined to the tropics, 16%), forest fires (mostly in the
extratropics, 15%), agricultural waste burning (3%), and tropical peat
fires (3%). The contribution from agricultural waste fires was likely a
lower bound because our approach for measuring burned area could not detect
all of these relatively small fires. Total carbon emissions were on average
13% lower than in our previous (GFED2) work. For reduced trace gases such
as CO and CH4, deforestation, degradation, and peat fires were more
important contributors because of higher emissions of reduced trace gases
per unit carbon combusted compared to savanna fires. Carbon emissions from
tropical deforestation, degradation, and peatland fires were on average 0.5 Pg C year−1.
The carbon emissions from these fires may not be balanced
by regrowth following fire. Our results provide the first global assessment
of the contribution of different sources to total global fire emissions for
the past decade, and supply the community with an improved 13-year fire
emissions time series.
In this study, we explored how rainfall manipulation influenced competitive interactions between grasses and juvenile trees (small nonreproductive trees capable of resprouting) in savanna. To do this, we manipulated rainfall amount in the field using an incomplete factorial experiment that determined the effects of rainfall reduction, no manipulation, rainfall addition, and competition between grasses and trees on grass and tree growth. As response variables, we focused on several measures of tree growth and Disc Pasture Meter settling height as an estimate of grass aboveground biomass. We conducted the study over four years, at two sites in the Kruger National Park, South Africa. Our results show that rainfall manipulation did not have substantial effects on any of the measures of tree growth we considered. However, trees at plots where grasses had been removed grew on average 15 cm more in height and 1.3-1.7 times more in basal area per year than those in plots with grasses. Grass biomass was not influenced by the presence of trees but was significantly and positively influenced by rainfall addition. These findings were not fundamentally influenced by soil type or by prevailing precipitation, suggesting applicability of our results to a wide range of savannas. Our results suggest that, in savannas, increasing rainfall serves to increase the competitive pressure exerted by grasses on trees. The implication is that recruitment into the adult tree stage from the juvenile stage is most likely in drought years when there is little competition from grass for resources and grass fuel loads are low.
Changes in climate and land use that interact synergistically to increase fire frequencies and intensities in tropical regions are predicted to drive forests to new grass-dominated stable states. To reveal the mechanisms for such a transition, we established 50 ha plots in a transitional forest in the southwestern Brazilian Amazon to different fire treatments (unburned, burned annually (B1yr) or at 3-year intervals (B3yr)). Over an 8-year period since the commencement of these treatments, we documented: (i) the annual rate of pasture and native grass invasion in response to increasing fire frequency; (ii) the establishment of Brachiaria decumbens (an African C4 grass) as a function of decreasing canopy cover and (iii) the effects of grass fine fuel on fire intensity. Grasses invaded approximately 200 m from the edge into the interiors of burned plots (B1yr: 4.31 ha; B3yr: 4.96 ha) but invaded less than 10 m into the unburned plot (0.33 ha). The probability of B. decumbens establishment increased with seed availability and decreased with leaf area index. Fine fuel loads along the forest edge were more than three times higher in grass-dominated areas, which resulted in especially intense fires. Our results indicate that synergies between fires and invasive C4 grasses jeopardize the future of tropical forests.
Fire is a ubiquitous component of the Earth system that is poorly understood. To date, a global-scale understanding of fire is largely limited to the annual extent of burning as detected by satellites. This is problematic because fire is multidimensional, and focus on a single metric belies its complexity and importance within the Earth system. To address this, we identified five key characteristics of fire regimes-size, frequency, intensity, season, and extent-and combined new and existing global datasets to represent each. We assessed how these global fire regime characteristics are related to patterns of climate, vegetation (biomes), and human activity. Cross-correlations demonstrate that only certain combinations of fire characteristics are possible, reflecting fundamental constraints in the types of fire regimes that can exist. A Bayesian clustering algorithm identified five global syndromes of fire regimes, or pyromes. Four pyromes represent distinctions between crown, litter, and grass-fueled fires, and the relationship of these to biomes and climate are not deterministic. Pyromes were partially discriminated on the basis of available moisture and rainfall seasonality. Human impacts also affected pyromes and are globally apparent as the driver of a fifth and unique pyrome that represents human-engineered modifications to fire characteristics. Differing biomes and climates may be represented within the same pyrome, implying that pathways of change in future fire regimes in response to changes in climate and human activity may be difficult to predict.
Inclusion of improved forest management as a way to enhance carbon sinks in the Copenhagen Accord of the United Nations Framework Convention on Climate Change (December 2009) suggests that forest restoration will play a role in global climate change mitigation under the post-Kyoto agreement. Although discussions about restoration strategies often pertain solely to severely degraded tropical forests and invoke only the enrichment planting option, different approaches to restoration are needed to counter the full range of degrees of degradation. We propose approaches for restoration of forests that range from being slightly to severely degraded. Our methods start with ceasing the causes of degradation and letting forests regenerate on their own, progress through active management of natural regeneration in degraded areas to accelerate tree regeneration and growth, and finally include the stage of degradation at which re-planting is necessary. We argue that when the appropriate techniques are employed, forest restoration is cost-effective relative to conventional planting, provides abundant social and ecological co-benefits, and results in the sequestration of substantial amounts of carbon. For forest restoration efforts to succeed, a supportive post-Kyoto agreement is needed as well as appropriate national policies, institutional arrangements, and local participation.
Keywords: Assisted natural regeneration, Biodiversity, Climate change agreement, Forest restoration, REDD-plus, Reduced-impact logging, Silviculture
▪ Abstract Savannas occur where trees and grasses interact to create a biome that is neither grassland nor forest. Woody and gramineous plants interact by many mechanisms, some negative (competition) and some positive (facilitation). The strength and sign of the interaction varies in both time and space, allowing a rich array of possible outcomes but no universal predictive model. Simple models of coexistence of trees and grasses, based on separation in rooting depth, are theoretically and experimentally inadequate. Explanation of the widely observed increase in tree biomass following introduction of commercial ranching into savannas requires inclusion of interactions among browsers, grazers, and fires, and their effects on tree recruitment. Prediction of the consequences of manipulating tree biomass through clearing further requires an understanding of how trees modify light, water, and nutrient environments of grasses. Understanding the nature of coexistence between trees and grass, which under other ci...
The REDD+ scheme of the United Nations intends to offer developing countries financial incentives to reduce the rates of deforestation and forest degradation for reducing global CO(2) emissions. This is combined with building carbon stocks in existing wooded ecosystems and fostering other soil, biodiversity and water conservation objectives. Successful application of REDD+ to the Xylophone Triangle of West Africa faces substantial challenges and risks to both meeting REDD+ objectives and to the local people's rights and livelihoods. The transnationality of the culturally coherent area requires collaboration of three national governments. The opportunities, however, are great to capitalize on the region's biodiversity, the well-developed traditional ecological knowledge and the use of local medicinal plants as an integral part of the agro-ecosystem. Possibilities open to, not only sequester carbon, but also to increase the resilience of the ecosystem and of independent rural livelihoods in the face of climate change and globalization.
Deforestation contributes 6-17% of global anthropogenic CO2
emissions to the atmosphere. Large uncertainties in emission estimates
arise from inadequate data on the carbon density of forests and the
regional rates of deforestation. Consequently there is an urgent need
for improved data sets that characterize the global distribution of
aboveground biomass, especially in the tropics. Here we use multi-sensor
satellite data to estimate aboveground live woody vegetation carbon
density for pan-tropical ecosystems with unprecedented accuracy and
spatial resolution. Results indicate that the total amount of carbon
held in tropical woody vegetation is 228.7PgC, which is 21% higher than
the amount reported in the Global Forest Resources Assessment 2010 (ref.
). At the national level, Brazil and Indonesia contain 35% of the total
carbon stored in tropical forests and produce the largest emissions from
forest loss. Combining estimates of aboveground carbon stocks with
regional deforestation rates we estimate the total net emission of
carbon from tropical deforestation and land use to be
1.0PgCyr-1 over the period 2000-2010--based on the carbon
bookkeeping model. These new data sets of aboveground carbon stocks will
enable tropical nations to meet their emissions reporting requirements
(that is, United Nations Framework Convention on Climate Change Tier 3)
with greater accuracy.
Inclusion of improved forest management as a way to enhance carbon sinks in the Copenhagen Accord of the United Nations Framework Convention on Climate Change (December 2009) suggests that forest restoration will play a role in global climate change mitigation under the post-Kyoto agreement. Although discussions about restoration strategies often pertain solely to severely degraded tropical forests and invoke only the enrichment planting option, different approaches to restoration are needed to counter the full range of degrees of degradation. We propose approaches for restoration of forests that range from being slightly to severely degraded. Our methods start with ceasing the causes of degradation and letting forests regenerate on their own, progress through active management of natural regeneration in degraded areas to accelerate tree regeneration and growth, and finally include the stage of degradation at which re-planting is necessary. We argue that when the appropriate techniques are employed, forest restoration is cost-effective relative to conventional planting, provides abundant social and ecological co-benefits, and results in the sequestration of substantial amounts of carbon. For forest restoration efforts to succeed, a supportive post-Kyoto agreement is needed as well as appropriate national policies, institutional arrangements, and local participation.
Woody plant increase in grassy biomes has been widely reported over the last century. Increases have been attributed to local drivers associated with land use change, such as heavy grazing or fire suppression, or, controversially, to global drivers such as increased atmospheric carbon dioxide (CO2). Here, we report a comparison of woody increase since the 1930s in three neighbouring areas with highly contrasting land use systems to help distinguish between local and global causes of woody increase. Aerial photography was used to measure changes in tree cover for three time intervals (1937, 1960, 2004) for three adjacent 25 km2 sites which remained under radically different tenure (conservation, commercial farms, and communal rangeland) over the study period. From previous studies on drivers affecting savanna dynamics, we predicted a decrease in tree cover for the conservation and communal sites and an increase in tree cover at the commercial site. The analyses showed highly significant increases in tree cover at all sites. Total tree cover increased from 14% in 1937 to 58% in 2004 at the conservation site, 3–50% in the commercial ranching area and 6–25% in the communal farming area. Reconstruction of past land use practices showed large differences in stocking rates, herbivore species, burning practices, human population densities and natural resource harvesting between the three sites. These land use differences are reflected in differences in woody cover among the three sites in 2004. However, despite major differences in land use, tree cover also increased significantly in all three areas. This suggests global drivers favouring woody plant increase in grassy vegetation regardless of land use practises. In our study area the most likely candidates are increased CO2 and/or atmospheric nitrogen deposition.
While research continues on the causes, consequences, and rates of deforestation and forest degradation in the tropics, there is little agreement about what exactly is being lost, what we want back, and to whom the ‘we’ refers. Particularly unsettling is that many analyses and well-intended actions are implemented in fogs of ambiguity surrounding definitions of the term ‘forest’—a problem that is not solely semantic; with development of markets for biomass carbon, vegetation classification exercises take on new relevance. For example, according to the basic implementation guidelines of the Kyoto Protocol, closed canopy natural forest could be replaced by monoclonal plantations of genetically engineered exotic tree species and no deforestation would have occurred. Following these same guidelines, carbon credits for afforestation could be available for planting trees in species-rich savannas; these new plantations would count towards a country moving towards the ‘forest transition,’ the point at which there is no net ‘forest’ loss. Such obvious conflicts between biodiversity conservation and carbon sequestration might be avoided if ‘forest’ was clearly defined and if other vegetation types and other ecosystem values were explicitly recognized. While acknowledging that no one approach to vegetation classification is likely to satisfy all users at all scales, we present an approach that recognizes the importance of species composition, reflects the utility of land-cover characteristics that are identifiable via remote sensing, and acknowledges that many sorts of forest degradation do not reduce carbon stocks (e.g., defaunation) or canopy cover (e.g., over-harvesting of understory nontimber forest products).
Context. Australia has a lamentable history of mammal extinctions. Until recently, the mammal fauna of northern Australia was presumed to have been spared such loss, and to be relatively intact and stable. However, several recent studies have suggested that this mammal fauna may be undergoing some decline, so a targeted monitoring program was established in northern Australia's largest and best-resourced conservation reserve. Aims. The present study aims to detect change in the native small-mammal fauna of Kakadu National Park, in the monsoonal tropics of northern Australia, over the period of 1996–2009, through an extensive monitoring program, and to consider factors that may have contributed to any observed change. Methods. The small-mammal fauna was sampled in a consistent manner across a set of plots established to represent the environmental variation and fire regimes of Kakadu. Fifteen plots were sampled three times, 121 plots sampled twice and 39 plots once. Resampling was typically at 5-yearly intervals. Analysis used regression (of abundance against date), and Wilcoxon matched-pairs tests to assess change. For resampled plots, change in abundance of mammals was related to fire frequency in the between-sampling period. Key results. A total of 25 small mammal species was recorded. Plot-level species richness and total abundance decreased significantly, by 54% and 71%, respectively, over the course of the study. The abundance of 10 species declined significantly, whereas no species increased in abundance significantly. The number of 'empty' plots increased from 13% in 1996 to 55% in 2009. For 136 plots sampled in 2001–04 and again in 2007–09, species richness declined by 65% and the total number of individuals declined by 75%. Across plots, the extent of decline increased with increasing frequency of fire. The most marked declines were for northern quoll, Dasyurus hallucatus, fawn antechinus, Antechinus bellus, northern brown bandicoot, Isoodon macrourus, common brushtail possum, Trichosurus vulpecula, and pale field-rat, Rattus tunneyi. Conclusions. The native mammal fauna of Kakadu National Park is in rapid and severe decline. The cause(s) of this decline are not entirely clear, and may vary among species. The most plausible causes are too frequent fire, predation by feral cats and invasion by cane toads (affecting particularly one native mammal species). Implications. The present study has demonstrated a major decline in a key conservation reserve, suggesting that the mammal fauna of northern Australia may now be undergoing a decline comparable to the losses previously occurring elsewhere in Australia. These results suggest that there is a major and urgent conservation imperative to more precisely identify, and more effectively manage, the threats to this mammal fauna.
The United Nations climate treaty may soon include a mechanism for compensating tropical nations that succeed in reducing carbon emissions from deforestation and forest degradation, source of nearly one fifth of global carbon emissions. We review the potential for this mechanism [reducing emissions from deforestation and degradation (REDD)] to provoke ecological damages and promote ecological cobenefits. Nations could potentially participate in REDD by slowing clear-cutting of mature tropical forest, slowing or decreasing the impact of selective logging, promoting forest regeneration and restoration, and expanding tree plantations. REDD could also foster efforts to reduce the incidence of forest fire. Potential ecological costs include the accelerated loss (through displaced agricultural expansion) of low-biomass, high-conservation-value ecosystems, and substitution of low-biomass vegetation by monoculture tree plantations. These costs could be avoided through measures that protect low-biomass native ecosystems. Substantial ecological cobenefits should be conferred under most circumstances, and include the maintenance or restoration of (1) watershed functions, (2) local and regional climate regimes, (3) soils and biogeochemical processes, (4) water quality and aquatic habitat, and (5) terrestrial habitat. Some tools already being developed to monitor, report and verify (MRV) carbon emissions performance can also be used to measure other elements of ecosystem function, making development of MRV systems for ecological cobenefits a concrete possibility. Analysis of possible REDD program interventions in a large-scale Amazon landscape indicates that even modest flows of forest carbon funding can provide substantial cobenefits for aquatic ecosystems, but that the functional integrity of the landscape's myriad small watersheds would be best protected under a more even spatial distribution of forests. Because of its focus on an ecosystem service with global benefits, REDD could access a large pool of global stakeholders willing to pay to maintain carbon in forests, thereby providing a potential cascade of ecosystem services to local stakeholders who would otherwise be unable to afford them.
C4 grasses constitute the main component of savannas and are pervasive in other dry tropical ecosystems where they serve as the main diet for grazing animals. Among potential factors driving C4 evolution of grasses, the interaction between grasses and grazers has not been investigated. To evaluate if increased grazing pressure may have selected for higher leaf silica production as the grasses diverged, we reconstructed the phylogeny of all 800 genera of the grass family with both molecular (combined multiplastid DNA regions) and morphological characters. Using molecular clocks, we also calculated the age and number of origins of C4 clades and found that shifts from C3 to C4 photosynthesis occurred at least 12 times starting 30.9 million years ago and found evidence that the most severe drop in atmospheric carbon dioxide in the late Oligocene (between 33 and 30 million years ago) matches the first origin of C4 photosynthesis in Chloridoideae. By combining fossil and phylogenetic data for ungulates and implementing a randomization procedure, our results showed that the appearance of C4 grass clades and ungulate adaptations to C4-dominated habitats match significantly in time. An increase of leaf epidermal density of silica bodies was found to correspond to postulated shifts in diversification rates in the late Miocene [24 significant shifts in diversification (P<0.05) were detected between 23 and 3.7 million years ago]. For aristidoid and chloridoid grasses, increased grazing pressure may have selected for a higher leaf epidermal silica production in the late Miocene.
Human impacts on the natural environment have reached such proportions that in addition to an ‘extinction crisis’, we now also face a broader ‘biome crisis’. Here we identify the world's terrestrial biomes and, at a finer spatial scale, ecoregions in which biodiversity and ecological function are at greatest risk because of extensive habitat conversion and limited habitat protection. Habitat conversion exceeds habitat protection by a ratio of 8 : 1 in temperate grasslands and Mediterranean biomes, and 10 : 1 in more than 140 ecoregions. These regions include some of the most biologically distinctive, species rich ecosystems on Earth, as well as the last home of many threatened and endangered species. Confronting the biome crisis requires a concerted and comprehensive response aimed at protecting not only species, but the variety of landscapes, ecological interactions, and evolutionary pressures that sustain biodiversity, generate ecosystem services, and evolve new species in the future.
Tree planting in the tropics is conducted for a number of reasons including carbon sequestration, but often competes with increasingly scarce water resources. The basics of forest and water relations are frequently said to be well understood but there is a pressing need to better understand and predict the hydrological effects of land-use and climate change in the complex and dynamic landscapes of the tropics. This will remain elusive without the empirical data required to feed hydrological process models. It is argued that the current state of knowledge is confused by too broad a use of the terms ‘forest’ and ‘(af)forestation’, as well as by a bias towards using data generated mostly outside the tropics and for nondegraded soil conditions. Definitions of forest, afforestation and reforestation as used in the climate change community and their application by land and water managers need to be reconciled.
Aim (1) To estimate the local and global magnitude of carbon fluxes between savanna and the atmosphere, and to suggest the significance of savannas in the global carbon cycle. (2) To suggest the extent to which protection of savannas could contribute to a global carbon sequestration initiative.
Location Tropical savanna ecosystems in Africa, Australia, India and South America.
Methods A literature search was carried out using the ISI Web of Knowledge, and a compilation of extra data was obtained from other literature, including national reports accessed through the personal collections of the authors. Savanna is here defined as any tropical ecosystem containing grasses, including woodland and grassland types. From these data it was possible to estimate the fluxes of carbon dioxide between the entire savanna biome on a global scale.
Results Tropical savannas can be remarkably productive, with a net primary productivity that ranges from 1 to 12 t C ha ⁻¹ year ⁻¹ . The lower values are found in the arid and semi‐arid savannas occurring in extensive regions of Africa, Australia and South America. The global average of the cases reviewed here was 7.2 t C ha ⁻¹ year ⁻¹ . The carbon sequestration rate (net ecosystem productivity) may average 0.14 t C ha ⁻¹ year ⁻¹ or 0.39 Gt C year ⁻¹ . If savannas were to be protected from fire and grazing, most of them would accumulate substantial carbon and the sink would be larger. Savannas are under anthropogenic pressure, but this has been much less publicized than deforestation in the rain forest biome. The rate of loss is not well established, but may exceed 1% per year, approximately twice as fast as that of rain forests. Globally, this is likely to constitute a flux to the atmosphere that is at least as large as that arising from deforestation of the rain forest.
Main conclusions The current rate of loss impacts appreciably on the global carbon balance. There is considerable scope for using many of the savannas as sites for carbon sequestration, by simply protecting them from burning and grazing, and permitting them to increase in stature and carbon content over periods of several decades.
If global policies intended to promote forest conservation continue to use the definition of “forest” adopted in 2001 by the United Nations Framework Convention on Climate Change (an area of >0.05–1 ha with >10–30% cover of plants >2–5 m tall at maturity), great quantities of carbon and other environmental values will be lost when natural forests are severely degraded or replaced by plantations but technically remain “forests.” While a definition of “forest” that is globally acceptable and appropriate for monitoring using standard remote sensing options will necessarily be based on a small set of easily measured parameters, there are dangers when simple definitions are applied locally. At the very least, we recommend that natural forest be differentiated from plantations and that for defining “forest” the lower height limit defining “trees” be set at more than 5 m tall with the minimum cover of trees be set at more than 40%. These changes will help reduce greenhouse gas emissions from what is now termed forest “degradation” without increasing monitoring costs. Furthermore, these minor changes in the definition of “forest” will promote the switch from degradation to responsible forest management, which will help mitigate global warming while protecting biodiversity and contributing to sustainable development.
C4 photosynthetic physiologies exhibit fundamentally different responses to temperature and atmospheric CO2 partial pressures (pCO2) compared to the evolutionarily more primitive C3 type. All else being equal, C4 plants tend to be favored over C3 plants in warm humid climates and, conversely, C3 plants tend to be favored over C4 plants in cool climates. Empirical observations supported by a photosynthesis model predict the existence of a climatological
crossover temperature above which C4 species have a carbon gain advantage and below which C3 species are favored. Model calculations and analysis of current plant distribution suggest that this pCO2-dependent crossover temperature is approximated by a mean temperature of 22°C for the warmest month at the current pCO2 (35 Pa). In addition to favorable temperatures, C4 plants require sufficient precipitation during the warm growing season. C4 plants which are predominantly graminoids of short stature can be competitively excluded by trees (nearly all C3 plants) – regardless of the photosynthetic superiority of the C4 pathway – in regions otherwise favorable for C4. To construct global maps of the distribution of C4 grasses for current, past and future climate scenarios, we make use of climatological data sets which provide estimates of
the mean monthly temperature to classify the globe into areas which should favor C4 photosynthesis during at least 1 month of the year. This area is further screened by excluding areas where precipitation
is <25 mm per month during the warm season and by selecting areas classified as grasslands (i.e., excluding areas dominated
by woody vegetation) according to a global vegetation map. Using this approach, grasslands of the world are designated as
C3, C4, and mixed under current climate and pCO2. Published floristic studies were used to test the accuracy of these predictions in many regions of the world, and agreement
with observations was generally good. We then make use of this protocol to examine changes in the global abundance of C4 grasses in the past and the future using plausible estimates for the climates and pCO2. When pCO2 is lowered to pre-industrial levels, C4 grasses expanded their range into large areas now classified as C3 grasslands, especially in North America and Eurasia. During the last glacial maximum (∼18 ka BP) when the climate was cooler
and pCO2 was about 20 Pa, our analysis predicts substantial expansion of C4 vegetation – particularly in Asia, despite cooler temperatures. Continued use of fossil fuels is expected to result in double
the current pCO2 by sometime in the next century, with some associated climate warming. Our analysis predicts a substantial reduction in the
area of C4 grasses under these conditions. These reductions from the past and into the future are based on greater stimulation of C3 photosynthetic efficiency by higher pCO2 than inhibition by higher temperatures. The predictions are testable through large-scale controlled growth studies and analysis
of stable isotopes and other data from regions where large changes are predicted to have occurred.
The savannas (cerrado) of south-central Brazil are currently subjected to frequent anthropogenic burning, causing widespread
reduction in tree density. Increasing concentrations of atmospheric CO2 could reduce the impact of such frequent burning by increasing the availability of nonstructural carbohydrate, which is necessary
for resprouting. We tested the hypotheses that elevated CO2 stimulates resprouting and accelerates replenishment of carbohydrate reserves. Using a factorial experiment, seedlings of
a common Brazilian savanna tree, Keilmeyera coriacea, were grown at 350 ppm and 700 ppm CO2 and at two nutrient levels. To simulate burning, the plants were either clipped at 15 weeks or were left unclipped. Among
unclipped plants, CO2 and nutrients both stimulated growth, with no significant interaction between nutrient and CO2 effects. Among clipped plants, both CO2 and nutrients stimulated resprouting. However, there was a strong interaction between CO2 and nutrient effects, with CO2 having a significant effect only in the presence of high nutrient availability. Under elevated CO2, carbohydrate reserves remained at higher levels following clipping. Root total nonstructural carbohydrate remained above
36% in all treatments, so carbohydrate reserves did not limit regrowth. These results indicate that under elevated CO2 this species may be better able to endure the high frequency of anthropogenic burning in the Brazilian savannas.
Global warming is contentious and difficult to measure, even among the majority of scientists who agree that it is taking place. Will temperatures rise by 2ºC or 8ºC over the next hundred years? Will sea levels rise by 2 or 30 feet? The only way that we can accurately answer questions like these is by looking into the distant past, for a comparison with the world long before the rise of mankind. We may currently believe that atmospheric shifts, like global warming, result from our impact on the planet, but the earth's atmosphere has been dramatically shifting since its creation. This book reveals the crucial role that plants have played in determining atmospheric change - and hence the conditions on the planet we know today. Along the way a number of fascinating puzzles arise: Why did plants evolve leaves? When and how did forests once grow on Antarctica? How did prehistoric insects manage to grow so large? The answers show the extraordinary amount plants can tell us about the history of the planet -- something that has often been overlooked amongst the preoccuputations with dinosaur bones and animal fossils. David Beerling's surprising conclusions are teased out from various lines of scientific enquiry, with evidence being brought to bear from fossil plants and animals, computer models of the atmosphere, and experimental studies. Intimately bound up with the narrative describing the dynamic evolution of climate and life through Earth's history, we find Victorian fossil hunters, intrepid polar explorers and pioneering chemists, alongside wallowing hippos, belching volcanoes, and restless landmasses.
Deforestation and forest degradation have continued over a long period of time, and the deterioration of forest environment management services is becoming one of the biggest concerns in the world. Especially in large continental river basins, sel? sh political attitudes and individual interests in some regions predispose other regions to problems downstream and bring about international issues. The Mekong is just such a river basin and its water is the most important resource, interdependent with the forest conditions in the region. The lives of millions of people are sustained by the water of the Mekong River, and mutual understanding on water resource mana- ment is essential in this region. Consequently, appropriate environment management to control water resources is required of each country along with scienti? c knowledge of forest management, including forest hydrology. The Mekong River Commission (MRC) was established in 1995 to jointly manage shared water resources and develop the economic potential of the river by the gove- ments of Cambodia, Laos, Thailand, and Vietnam. However, very limited operational forest management for water resources is being conducted based on reliable sources of information. International cooperation in science and technology has progressed in Southeast Asia. One such activity, the research project “Changes of Water Cycle in the Mekong River Basin” (CWCM), has been conducted by the Forestry Administration (FA) of Cambodia, the Forestry and Forest Products Research Institute (FFPRI) of Japan, and several universities, since 2002.
This study reviews how West African deforestation is represented and the evidence which informs deforestation orthodoxy. On a country by country basis (covering Sierra Leone, Liberia, Cote D'Ivoire, Ghana, Togo and Benin), and using historical and social anthropological evidence the authors evaluate this orthodox critically. Reframing Deforestation suggests that the scale of deforestation wrought by West African farmers during the twentieth century has been vastly exaggerated. The authors argue that global analyses have unfairly stigmatised West Africa and obscured its more sustainable, even landscape-enriching practices. Stessing that dominant policy approaches in forestry and conservation require major rethinking worldwide, Reframing Deforestation illustrates that more realistic assessments of forest cover change, and more respectful attention to local knowledge and practices, are necessary bases for effective and appropriate environmental policies.
This paper offers a review and reassessment of the biogeography of the Afromontane region. Much of the montane vegetation of Africa, expecially in the sourthern part of its distribution (the southern Afromontane region) is characterized by a mosaic of forest `islands' in a `sea' of grassland, with or without heathland elements. Controversy has arisen as to the origin of these grasslands and the view has emerged, based on a variety of phytogeographical, zoogeographical, ecological, pedological and historical evidence, that the grasslands element has been derived, or at least markeldy extended, in the recent past by forest clearance through human agency. An alternative hypothesis holds that the grassland is a much older component of the Afromontage landscape. The paper assesses these two opposing viewpoints in the light of published palaeoecological and biogeographical evidence not previously brought to bear on the problem of Afromontane grassland origins in general. The physical environment and vegetation of the southern Afromontane region is reviewed and the suggestions put forward to account for the widespread occurrence of grasslands in the region are presented. The competing hypotheses are then tested against data on plant species richness and diversity from a number of upland areas within the region and against published Quaternary palynological data from the Nyika Plateau, Malawi, the Inyaga Mountains, Zimbabwe and the Winterberg Escarpment area of South Africa. The resulting reassessment offers strong support for the idea that the grasslands have been prominent in the southern Afromontane region since before the permanent occupation of the mountains by people. Environmental changes, especially of the late Quaternary, are suggested as having been important in establishing the vegetation pattern and, while increased magnitude of human impact in recent times is apparent, the so-called `relict' nature of montane forest patches is questionable. It is argued that the southern Afromontane grasslands are themselves relict from a time, around the last glacial maximum, when the climatic conditions were more suited to these formations than to forest.
Savanna burning for greenhouse gas abatement presents an opportunity for remote Aboriginal communities of northern Australia to engage with the mainstream economy while fulfilling cultural obligations for land stewardship. The recently established Tiwi Carbon Study aims to identify the biophysical and economic potential of fire management for greenhouse gas abatement on the Tiwi Islands north of Darwin, as a basis for possible livelihood opportunities for the Aboriginal Tiwi people. Recent (2001–2010) fire history for the Tiwi Islands based on AVHRR satellite imagery shows that on average 35% (187 700 ha) of its savanna woodlands and open forests are burned every year, with 72% of burning occurring late in the dry season (August to November). Non‐CO2 greenhouse gas emissions from Tiwi fires average 68 000 t CO2‐e year−1 and we discuss scenarios for greenhouse gas abatement through management of these fires by Tiwi people, consistent with the savanna burning methodology approved under the Federal Government's Carbon Farming Initiative. Changed fire management scenarios produced emissions abatement of up to 46 000 t CO2‐e year−1, with highest savings under a change in both fire frequency and intensity. In addition to abatement of non‐CO2 emissions, fire management has the potential to alter rates of carbon sequestered in soil and vegetation. Current ecosystem C stocks (excluding roots) on the Tiwi Islands range from 60 to 160 t C ha−1. The Tiwi Carbon Study features a long‐term, landscape‐scale fire experiment for informing full carbon accounting in relation to different fire management options, and for understanding their implications for biodiversity. We discuss potential co‐benefits and trade‐offs of fire management for greenhouse gas emissions abatement in relation to biodiversity and Tiwi cultural requirements and livelihood aspirations.
Tropical savannas are the world's most fire‐prone biome, and savanna biotas are generally well adapted to frequent fire. However, in northern Australia there are concerns that recent increases in the frequency and extent of high‐intensity fires are causing substantial declines in regional biodiversity values. In this paper we use two well‐studied and contrasting faunal groups, ants and small mammals, as case studies for reviewing faunal responses to fire in Australian savannas. The Australian savanna ant fauna is dominated by arid‐adapted taxa that are highly resilient to frequent fire and are not considered to be threatened by prevailing fire regimes. Indeed, frequent fire promotes ant diversity because it maintains an open habit that makes the dominant arid‐adapted taxa feel at home. Long‐term fire exclusion reduces ant diversity due to a marked decline in arid‐adapted taxa, and favours highly generalized, more shade‐tolerant taxa. In contrast, many small mammal species of high conservation value are highly sensitive to frequent fire, and there are widespread concerns that their populations are threatened by current fire management. Many of the species have shown dramatic population declines over recent decades, and, although the causes are poorly understood, there is little doubt that fire is an important contributing factor. It is likely that fire is acting synergistically with other underlying causes of decline, particularly predation by feral cats. The overall resilience of most savanna animal species in relation to frequent fire suggests that they are secure under all but the most extreme fire regimes. However, it is clear that more fire‐sensitive groups such as small mammals need special fire management attention. This needs to involve less frequent and finer‐scale burning, along with the protection of some large, infrequently burnt source areas.
The higher flammability of tropical savanna, compared with forest, plays a critical role in mediating vegetation‐environment feedbacks, alternate stable states, and ultimately, the distribution of these two biomes. Multiple factors contribute to this difference in flammability, including microclimate, fuel amount and fuel type. To understand this transition in flammability, we studied fuel characteristics and microclimate across eight savanna–forest boundaries in south‐central Brazil. At each boundary, the environment was monitored for one week with automated measurements of near‐surface wind speed, air temperature, relative humidity and presence of dew. Manual measurements were performed to quantify fuel amounts and fuel moisture. These data were used to parameterize the fire behaviour model BehavePlus5 in order to simulate fire behaviour over the savanna–forest boundary. There were strong gradients across the boundary in all variables with the exception of total fuel load. During the day, savannas had higher wind speed and air temperature, and lower relative humidity and fuel moisture than forests. Although fuel loads were similar in savanna and forest, savanna was characterized by lower fuel bulk density, largely because of the presence of grasses. Based on these measurements, the fire behaviour model predicted savanna fires to be faster, more intense, and with greater flame lengths, relative to forest. A sensitivity analysis indicated that the primary cause of these differences was the low fuel bulk density characteristic of grassy fuels, with lesser contributions from wind speed, fuel moisture and total fuel load. These results indicate that the dominance of grassy fuels is the primary cause of the high flammability of savanna.
Aim At a regional scale, across southern Africa, woody thickening of savannas is becoming increasingly widespread. Using coupled vegetation and faunal responses (ants), we explore whether major changes in woody cover in savannas represent an increase in the density of savanna trees (C4 grass layer remains intact) or a ‘regime shift’ in system state from savanna to thicket (=dry forest) where broad-leaved, forest-associated trees shade out C4 grasses.
Location Hluhluwe Game Reserve, South Africa.
Methods We sampled paired open (low woody cover) and closed (high cover that have undergone an increase in tree density) sites. Vegetation was sampled using belt transects, and a combination of pitfall trapping and Winkler sampling was used for ants.
Results Closed habitats did not simply contain a higher density of woody savanna species, but differed significantly in structure, functional composition (high prevalence of broad-leaved trees, discontinuous C4 grasses) and system properties (e.g. low flammability). Ant assemblage composition reflected this difference in habitat. The trophic structure of ant assemblages in the two habitats revealed a functional shift with much higher abundances of predatory species in the closed habitat.
Main conclusions The predominance of species with forest-associated traits and concomitant reduction of C4 grasses in closed sites indicate that vegetation has undergone a shift in fundamental system state (to thicket), rather than simply savanna thickening. This biome shift has cascading functional consequences and implications for biodiversity conservation. The potential loss of many specialist savanna plant species is especially concerning, given the spatial extent and speed of this vegetation switch. Although it is not clear how easily the habitat switch can be reversed and how stable the thicket habitats are, it is likely in the not-too-distant future that conservation managers will be forced to make decisions on whether to actively maintain savannas.
Though the distribution of global vegetation can generally be predicted from climate, grasslands are an exception. C4 grassy biomes cover vast areas that are warm enough and wet enough to support closed forests. The extent of this climate mismatch has been revealed by physiologically based global vegetation simulations and by large empirical data sets. Reasons for the existence of grassy biomes have long been debated, polarized into bottom-up (resources) or top-down (fire, herbivory) arguments. Recent studies indicate that both are important, especially in suppressing woody recruits. Grasses are formidable competitors belowground, create highly flammable fuels, and can support large herbivore densities. The net effect on trees is rare and episodic recruitment of adults in tree-fall gaps. The implication is that ecosystem structure and function depend on demographic transitions. Tree cover is increasing and grass/forest boundaries are changing. These changes can have large feedbacks to the earth-atmosphere system. Though progress has been made, there is still great uncertainty in predicting the future of C4 grassy biomes.
Forests and grassy vegetation (savannas and grasslands) are alternative ecosystem states in many tropical landscapes. Relative to forests the grassy ecosystems are poorly known and poorly conserved, partly because they were thought to be products of forest clearance. However many grasslands have proved to be ancient. Commensurate with their antiquity, grassy biomes have distinct suites of plant and animal species that contribute a large fraction of the diversity of forest–grassland mosaics. Grasslands differ strikingly from forests in their ecology and in the nature of threats to their future. Here we highlight the high biodiversity value of grassy biomes and, in contrast to tropical forests, we illustrate the importance of fire in maintaining these systems. We discuss the major threats to, and consequences for, biodiversity in these regions including land clearance and elevated CO2-driven forest expansion. Finally we focus on the difficulties of grassland restoration. A new approach to understanding and conserving grassy ecosystems, free from cultural prejudices of the past, is long overdue.
Unlabelled:
•
Premise of the study:
Climate-induced forest retreat has profound ecological and biogeochemical impacts, but the physiological mechanisms underlying past tree mortality are poorly understood, limiting prediction of vegetation shifts with climate variation. Climate, drought, fire, and grazing represent agents of tree mortality during the late Cenozoic, but the interaction between drought and declining atmospheric carbon dioxide ([CO2]a) from high to near-starvation levels ∼34 million years (Ma) ago has been overlooked. Here, this interaction frames our investigation of sapling mortality through the interdependence of hydraulic function, carbon limitation, and defense metabolism. •
Methods:
We recreated a changing Cenozoic [CO2]a regime by growing Sequoia sempervirens trees within climate-controlled growth chambers at 1500, 500, or 200 ppm [CO2]a, capturing the decline toward minimum concentrations from 34 Ma. After 7 months, we imposed drought conditions and measured key physiological components linking carbon utilization, hydraulics, and defense metabolism as hypothesized interdependent mechanisms of tree mortality. •
Key results:
Catastrophic failure of hydraulic conductivity, carbohydrate starvation, and tree death occurred at 200 ppm, but not 500 or 1500 ppm [CO2]a. Furthermore, declining [CO2]a reduced investment in carbon-rich foliar defense compounds that would diminish resistance to biotic attack, likely exacerbating mortality. •
Conclusions:
Low-[CO2]a-driven tree mortality under drought is consistent with Pleistocene pollen records charting repeated Californian Sequoia forest contraction during glacial periods (180-200 ppm [CO2]a) and may even have contributed to forest retreat as grasslands expanded on multiple continents under low [CO2]a over the past 10 Ma. In this way, geologic intervals of low [CO2]a coupled with drought could impose a demographic bottleneck in tree recruitment, driving vegetation shifts through forest mortality.
Aim This study investigates changes in bird communities between 1998 and 2008
in four savanna sites in Swaziland and the extent to which shrub encroachment is
responsible for these changes.
Location Swaziland, southern Africa.
Methods Generalized estimated equations were used to estimate changes in bird
species occurrence between 1998 and 2008. Remote sensing of aerial photographs/
satellite images was used to assess vegetation changes during the same period. We
assessed the role of shrub encroachment for bird communities by testing the
relationship between change in species occurrence and species habitat using a
general linear model. We also estimated species richness, colonization and
extinction and used general linear models to test the effects of vegetation changes
on these parameters.
Results More than half of the bird species showed a significant change in
occurrence between 1998 and 2008: 32 species increased and 29 decreased.
Change in species occurrence was significantly explained by species habitat.
Species significantly increasing were mainly associated with wooded savanna,
whereas species significantly decreasing were mainly associated with open
savanna. Species richness decreased significantly, and this decrease was
significantly explained by shrub cover increase at the plot scale (from 24% to
44% on average). Extinction at the plot scale was significantly influenced by the
loss of grass cover, while colonization at the plot scale was influenced by tree cover
increase.
Main conclusions This study represents the first evidence of temporal changes in
bird communities owing to shrub encroachment in southern Africa. Despite its
short time frame (10 years), this study shows dramatic changes in both vegetation
structure and bird community composition. This confirms the general concern
for southern African bird species associated with open savanna if current trends
continue.
The coastal grasslands in north-eastern South Africa are a severely threatened vegetation type rich in plant species, particularly forbs. Many of the forbs have underground storage organs which allow them to resprout rapidly after fires. A significant portion of this land was placed under commercial pine afforestation in the 1950s. The pine plantations have since been removed starting 17 years ago and restored to grasslands within a conservation area. We assessed the effects of plantations on grassland plant diversity and functional trait composition by sampling 64 circular quadrats of 5 m radius distributed equally in restored versus natural grasslands. The difference in plant diversity was dramatic with the natural grassland supporting 221 species of which 163 were forbs compared with 144 and only 73 forb species in restored grasslands. Major differences in species composition were recorded, especially for forb species. Natural grasslands were dominated by resprouters (130 species) but these were rare in the restored grasslands (36 species). Differences in plant species response to fire were also evident for the two grassland states. In contrast to coastal forest restoration studies in the same area which have shown near linear increases in woody species with time, restored grasslands showed no increase in forb species richness with increasing time since clear-felling of pines. Our results indicate that current methods for restoring these grasslands are inadequate and that restoring grasslands may be a lot harder than previously thought. Considerable effort should be made in conserving what is left of natural grasslands.
Savannas are defined based on vegetation structure, the central concept being a discontinuous tree cover in a continuous grass understorey. However, at the high-rainfall end of the tropical savanna biome, where heavily wooded mesic savannas begin to structurally resemble forests, or where tropical forests are degraded such that they open out to structurally resemble savannas, vegetation structure alone may be inadequate to distinguish mesic savanna from forest. Additional knowledge of the functional differences between these ecosystems which contrast sharply in their evolutionary and ecological history is required. Specifically, we suggest that tropical mesic savannas are predominantly mixed tree–C4 grass systems defined by fire tolerance and shade intolerance of their species, while forests, from which C4 grasses are largely absent, have species that are mostly fire intolerant and shade tolerant. Using this framework, we identify a suite of morphological, physiological and life-history traits that are likely to differ between tropical mesic savanna and forest species. We suggest that these traits can be used to distinguish between these ecosystems and thereby aid their appropriate management and conservation. We also suggest that many areas in South Asia classified as tropical dry forests, but characterized by fire-resistant tree species in a C4 grass-dominated understorey, would be better classified as mesic savannas requiring fire and light to maintain the unique mix of species that characterize them.
Abstract This opportunistic study compares the vegetation, fuel loads and vertebrate fauna of part of a 120-ha block of tropical open forest protected from fire for 23 years, and an adjacent block burnt annually over this period. Total fuel loads did not differ significantly between the unburnt and annually burnt sites, but their composition was markedly different, with far less grassy fuel, but far more litter fuel, in the unburnt block. There were major differences between treatments in the composition of trees and shrubs, manifest particularly in the number of stems. There was no overall difference in plant species richness between the two treatments, but richness of woody species was far higher in the unburnt treatment, and of annual and perennial grasses, and perennial herbs in the annually burnt treatment. Change in plant species composition from annually burnt to unburnt treatment was directional, in that there was a far higher representation of rainforest-associated species (with the percentage of woody stems attributable to ‘rainforest’ species increasing from 24% of all species in the annually burnt treatment to 43% in the unburnt treatment, that of basal area from 9% to 30%, that of species richness from 8% to 17%, and that of cover from 12 to 47%). The vertebrate species composition varied significantly between treatments, but there was relatively little difference in species richness (other than for a slightly richer reptile fauna in the unburnt treatment). Again, there was a tendency for species that were more common in the unburnt treatment to be rainforest-associated species. The results from this study suggest that there is a sizeable and distinct set of species that are associated with relatively long-unburnt environments, and hence that are strongly disadvantaged under contemporary fire regimes. We suggest that such species need to be better accommodated by fire management through strategic reductions in the frequency of burning.
Atmospheric CO2 has more than doubled since the last glacial maximum (LGM) and could double again within this century, largely due to anthropogenic activity. It has been suggested that low [CO2] contributed to reduced tree cover in savanna and grassland biomes at LGM, and that increasing [CO2] over the last century promoted increases in woody plants in these ecosystems over the past few decades. Despite the implications of this idea for understanding global carbon cycle dynamics and key global role of the savanna biome, there are still very few experimental studies quantifying the effects of CO2 on tree growth and demography in savannas and grasslands. In this paper we present photosynthetic, growth and carbon allocation responses of African savanna trees (Acacia karroo and Acacia nilotica) and a C4 grass, Themeda triandra, exposed to a gradient of CO2 concentrations from 180 (typical of LGM) to 1000 µmol mol−1 in open-top chambers in a glasshouse as a first empirical test of this idea. Photosynthesis, total stem length, total stem diameter, shoot dry weight and root dry weight of the acacias increased significantly across the CO2 gradient, saturating at higher CO2 concentrations. After clipping to simulate fire, plants showed an even greater response in total stem length, total stem diameter and shoot dry weight, signalling the importance of re-sprouting following disturbances such as fire or herbivory in savanna systems. Root starch (per unit root mass and total root starch per plant) increased steeply along the CO2 gradient, explaining the re-sprouting response. In contrast to the strong response of tree seedlings to the CO2 gradient, grass productivity showed little variation, even at low CO2 concentrations. These results suggest that CO2 has significant direct effects on tree recruitment in grassy ecosystems, influencing the ability of trees to recover from fire damage and herbivory. Fire and herbivore regimes that were effective in controlling tree increases in grassy ecosystems could thus be much less effective in a CO2-rich world, but field-based tests are needed to confirm this suggestion.
Managed grazing covers more than 25% of the global land surface and has a larger geographic extent than any other form of land use. Grazing systems per-sist under marginal bioclimatic and edaphic conditions of different biomes, leading to the emergence of three regional syndromes inherent to global grazing: desertification, woody encroachment, and deforestation. These syndromes have widespread but differ-ential effects on the structure, biogeochemistry, hydrology, and biosphere-atmosphere exchange of grazed ecosystems. In combination, these three syndromes represent a major component of global environmental change.
It is possible that anthropogenic climate change will drive the Earth system into a qualitatively different state. Although different types of uncertainty limit our capacity to assess this risk, Earth system scientists are particularly concerned about tipping elements, large-scale components of the Earth system that can be switched into qualitatively different states by small perturbations. Despite growing evidence that tipping elements exist in the climate system, whether large-scale vegetation systems can tip into alternative states is poorly understood. Here we show that tropical grassland, savanna and forest ecosystems, areas large enough to have powerful impacts on the Earth system, are likely to shift to alternative states. Specifically, we show that increasing atmospheric CO2 concentration will force transitions to vegetation states characterized by higher biomass and/or woody-plant dominance. The timing of these critical transitions varies as a result of between-site variance in the rate of temperature increase, as well as a dependence on stochastic variation in fire severity and rainfall. We further show that the locations of bistable vegetation zones (zones where alternative vegetation states can exist) will shift as climate changes. We conclude that even though large-scale directional regime shifts in terrestrial ecosystems are likely, asynchrony in the timing of these shifts may serve to dampen, but not nullify, the shock that these changes may represent to the Earth system.
Aim Grasslands and savannas, which make up > 75% of Madagascar’s land area, have long been viewed as anthropogenically derived after people settled on the island c . 2 ka. We investigated this hypothesis and an alternative – that the grasslands are an insular example of the post‐Miocene spread of C 4 grassy biomes world‐wide.
Location Madagascar, southern Africa, East Africa.
Methods We compared the number of C 4 grass genera in Madagascar with that in southern and south‐central African floras. If the grasslands are recent we would expect to find fewer species and genera in Madagascar relative to Africa and for these species and genera to have very wide distribution ranges in Madagascar. Secondly, we searched Madagascan floras for the presence of endemic plant species or genera restricted to grasslands. We also searched for evidence of a grassland specialist fauna with species endemic to Madagascar. Plant and animal species endemic to C 4 grassy biomes would not be expected if these are of recent origin.
Results Madagascar has c . 88 C 4 grass genera, including six endemic genera. Excluding African genera with only one or two species, Madagascar has 86.6% of southern Africa’s and 89.4% of south‐central Africa’s grass genera. C 4 grass species make up c. 4% of the flora of both Madagascar and southern Africa and species : genus ratios are similar (4.3 and 5.1, respectively). Turnover of grasses along geographical gradients follows similar patterns to those in South Africa, with Andropogoneae dominating in mesic biomes and Chlorideae in semi‐arid grassy biomes. At least 16 monocot genera have grassland members, many of which are endemic to Madagascar. Woody species in frequently burnt savannas include both Madagascan endemics and African species. A different woody flora, mostly endemic, occurs in less frequently burnt grasslands in the central highlands, filling a similar successional niche to montane C 4 grasslands in Africa. Diverse vertebrate and invertebrate lineages have grassland specialists, including many endemic to Madagascar (e.g. termites, ants, lizards, snakes, birds and mammals). Grassland use of the extinct fauna is poorly known but carbon isotope analysis indicates that a hippo, two giant tortoises and one extinct lemur ate C 4 or CAM (crassulacean acid metabolism) plants.
Main conclusions The diversity of C 4 grass lineages in Madagascar relative to that in Africa, and the presence of plant and animal species endemic to Madagascan grassy biomes, does not fit the view that these grasslands are anthropogenically derived. We suggest that grasslands invaded Madagascar after the late Miocene, part of the world‐wide expansion of C 4 grassy biomes. Madagascar provides an interesting test case for biogeographical analysis of how these novel biomes assembled, and the sources of the flora and fauna that now occupy them. A necessary part of such an analysis would be to establish the pre‐settlement extent of the C 4 grassy biomes. Carbon isotope analysis of soil organic matter would be a feasible method for doing this.
Increasing densities of woody plants in savannas has been attributed to both elevated atmospheric CO2 and reduced burning with grazing management, such that the biome could represent a substantial carbon sink. However, we show that extreme droughts (less than two-thirds expected rainfall over 3 years) occur in the drier half of the savanna biome and can cause substantial tree death. An Australian case study reveals that a net increase in tree cover over five decades of above-average rainfall was offset by sudden tree death during drought. The relationship between woody cover change and rainfall is moderated by competition with growth being facilitated by low woody cover and drought-induced death more likely as the woody component of savanna increases. The results are not supportive of a sustained increase in the woody component of xeric savannas resulting from CO2 fertilization or land management. Extensive tree death in savanna regions will become a stark consequence of climate change if predictions of increasing severity and frequency of drought are realized.
Summary 341
Acknowledgements 365
References 365
C4 photosynthesis is a series of anatomical and biochemical modifications that concentrate CO2 around the carboxylating enzyme Rubisco, thereby increasing photosynthetic efficiency in conditions promoting high rates of photorespiration. The C4 pathway independently evolved over 45 times in 19 families of angiosperms, and thus represents one of the most convergent of evolutionary phenomena. Most origins of C4 photosynthesis occurred in the dicots, with at least 30 lineages. C4 photosynthesis first arose in grasses, probably during the Oligocene epoch (24–35 million yr ago). The earliest C4 dicots are likely members of the Chenopodiaceae dating back 15–21 million yr; however, most C4 dicot lineages are estimated to have appeared relatively recently, perhaps less than 5 million yr ago. C4 photosynthesis in the dicots originated in arid regions of low latitude, implicating combined effects of heat, drought and/or salinity as important conditions promoting C4 evolution. Low atmospheric CO2 is a significant contributing factor, because it is required for high rates of photorespiration. Consistently, the appearance of C4 plants in the evolutionary record coincides with periods of increasing global aridification and declining atmospheric CO2. Gene duplication followed by neo- and nonfunctionalization are the leading mechanisms for creating C4 genomes, with selection for carbon conservation traits under conditions promoting high photorespiration being the ultimate factor behind the origin of C4 photosynthesis.