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Burn scar classifications of Landsat 7 remote sensing imagery: (A) 2001 image acquired 15/09/2001, (B) 2002 image acquired on 11/10/2002. Burn scar classification accuracy = 91.8%.
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Herbivory can change the structure and spatial heterogeneity of vegetation. We ask whether all species of grazers in a savanna ecosystem can have this effect or whether megaherbivores (>1000 kg) have a 'special' role that cannot be replicated by other species of grazers. We performed a replicated landscape scale experiment that examined the effects...
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... Archibald & Hempson, 2016;Waldram et al., 2008) and factors such as rainfall (Johnson et al., 2018;Staver et al., 2021), which strongly constrains both grazing and fire activity across their highly varied range from 300 to 1500 mm/yr (Archibald et al., 2009;Krawchuk & Moritz, 2011;van Wilgen et al., 2000).A recent synthesis suggested that grazing effects on herbaceous biomass increase with the density of grazing herbivores but could not establish the influences of environmental variables, including rainfall and soil texture (Staver et al., 2021). Rainfall controls trade offs between grass nutrient content and quantity (Coe et al., 1976), while soil texture is related to soil fertility, which may increase the forage quality of herbaceous plants (Bell, 1984), thereby regulating grazing herbivore densities (East, 1984; and shaping grazing effects indirectly. ...
... Grazing effects on herbaceous biomass translated directly into impacts on fire. Past work showed that reductions in grazing populations result in increased BA and vice versa at local (intra-reserve) scales (Norton-Griffiths, 1979;Smit & Archibald, 2019;Waldram et al., 2008). Here, we showed wild grazing populations may also substantially reduce fires at broad spatial (inter-reserve) scales, supporting the hypothesis that biomass consumption by grazing herbivores and fire are strongly interconnected across African savannas (Archibald & Hempson, 2016). ...
... Burned area absolute and proportional reductions (ΔBA and ΔBA/BA potential ) increased strongly with grazing herbivore metabolic density (Figure 5c; Figure S7a; Table S12). The proportional model (ΔBA/BA potential ) also indicated larger fire reductions at lower rainfall (Figure S7b,c; Table S12), which is consistent with the observation that fuel loads primarily constrain fire spread (Alvarado et al., 2020;Archibald et al., 2009;Waldram et al., 2008) in semi-arid savannas. Even if herbivore consumption of fuels is consistent across rainfall (Figure 3f-i), the same grazing herbivore metabolic density more strongly excludes fire at lower overall grass productivity (Archibald et al., 2009;Smit & Archibald, 2019) (Figure S7). ...
Fire and herbivory interact to alter ecosystems and carbon cycling. In savannas, herbivores can reduce fire activity by removing grass biomass, but the size of these effects and what regulates them remain uncertain. To examine grazing effects on fuels and fire regimes across African savannas, we combined data from herbivore exclosure experiments with remotely sensed data on fire activity and herbivore density. We show that, broadly across African savannas, grazing herbivores substantially reduce both herbaceous biomass and fire activity. The size of these effects was strongly associated with grazing herbivore densities, and surprisingly, was mostly consistent across different environments. A one‐zebra increase in herbivore biomass density (~100 kg/km² of metabolic biomass) resulted in a ~53 kg/ha reduction in standing herbaceous biomass and a ~0.43 percentage point reduction in burned area. Our results indicate that fire models can be improved by incorporating grazing effects on grass biomass.
... The ways in which megaherbivores utilise their habitats at various spatial and temporal scales, and the distribution of the drivers of this space-use (e.g. vegetation type, water sources, anthropogenic factors), cause a range of habitat modifications and influences on vegetation dynamics, ultimately affecting species assemblages (Owen-Smith 1988;Bailey et al. 1996;Olff and Ritchie 1998;James et al. 1999;Knapp et al. 1999;Ogada et al. 2008;Waldram et al. 2008;Hyvarinen et al. 2021). High densities of megaherbivores can increase both the browsing and grazing pressure in an area, leading to a decline in vegetation regeneration and a loss of vegetation structural diversity (Bell 1971;Barnes 1982;Lewis 1986;Landman et al. 2008;Landman et al. 2014). ...
Heterogeneity, the spatio-temporal variation of abiotic and biotic factors, is a key concept that underpins many ecological phenomena and promotes biodiversity. Ecosystem engineers, such as African savanna elephants (hereafter elephant), Loxodonta africana, are organisms capable of affecting heterogeneity through the creation or modification of habitats. Thus, their impacts can have important consequences for ecosystem biodiversity, both positive and negative. Caughley’s “elephant problem” cautions that confined or compressed, growing elephant populations will inevitably lead to a loss of biodiversity. However, a shift in our understanding of elephants suggests that not all elephant impacts lead to negative biodiversity consequences, as long as there is a heterogeneous spread of elephant impacts that allows for spatio-temporal refuges promoting the persistence of both impact-tolerant and impact-intolerant species. To date, little empirical evidence is available in support of managing elephants under this paradigm and few studies are available that infer the consequences of the distribution of elephant impacts on biodiversity. In addition, most studies use parametric statistics that do not account for scale, spatial autocorrelation, or non-stationarity, leading to a misrepresentation of the underlying processes and patterns of drivers of elephant space-use and the consequences of their impacts on biodiversity. Here, I evaluate spatio-temporal patterns and drivers of elephant space-use, and how the distribution of their impacts affects biodiversity through vegetation changes, using a multi-scaled spatial approach, in Liwonde National Park, Malawi. My study demonstrates that elephant space-use in Liwonde is heterogeneous, leading to spatio-temporal variation in the distribution of their impacts, even in a small, fenced reserve. The importance of the drivers of this heterogeneous space-use varied based on the scale of analysis, water was generally important at larger scales while vegetation quality (indexed by NDVI) was more important at smaller scales. When examined using local models, my results suggest that relationships exhibit non-stationarity, what is important in one area of the park is not necessarily important in other areas. The spatio-temporal variation of the inferred impacts of elephants in Liwonde still allowed for spatio-temporal refuges to be created, no clear linear relationship was found between elephant return intervals and woody species structural and functional diversity (indexed by changes in tree cover and changes in annual regrowth using Normalized Difference Vegetation Index as a measure, respectively) throughout the park. My study provides support for adopting the heterogeneity paradigm for managing elephants and demonstrates that not all elephant impacts result in negative vegetation change. I also demonstrate the crucial implications of accounting for scale, non-stationarity, and spatial autocorrelation to evaluate how animals both respond to, and contribute to, environmental heterogeneity.
... In the same study, the authors note that mesoherbivores shifted communities towards dominance by species with low SLA and leaf nutrition, but that in the longer term larger grazers had stronger effects on the same traits (van der Plas et al., 2016). Surprisingly however, the largest species in the experiment, white rhinoceros, did not have detectable effects on vegetation structure or composition over the study period, contrasting general findings for this species (Waldram et al., 2008). Considering the type, intensity, of herbivory provides important nuance on the potential overall effect and spatiotemporal heterogeneity in the effects of trophic rewilding on ecosystem function. ...
Trophic rewilding is gaining rapid momentum as a means of restoration across the world. Advances in research are elucidating the wide‐ranging effects of trophic rewilding and megafauna re‐establishment on ecosystem properties and processes including resilience, nutrient cycling, carbon sequestration, productivity and plant richness.
A substantial gap remains in trophic rewilding research on how rewilding affects the frequency and expression of plant functional traits, a key hypothesised avenue by which megafauna can affect biodiversity and ecosystem processes. Yet, there is extensive literature examining the effects of mammal herbivory and exclusion on plant traits from which we may infer potential effects of megafauna reintroductions.
Here, we synthesise the literature to show the multifaceted ways that plant functional composition responds to mammalian herbivory and explore how these responses are modulated by the density and identity of herbivores as well as resource availability, ecosystem productivity and historical contingency. We further explore these interactions in a quantitative analysis on European plant species. In addition, we link these broad patterns between mammal herbivory and traits to literature on plant invasions to predict how trophic rewilding may be able to reduce invasive plant dominance, as ecosystems around the world are transitioning towards novel states, occupied by a mix of native and introduced species.
Expanding current research on herbivore effects (and their implications for trophic rewilding) beyond plant species richness and towards measurable functional traits can help assess and quantify processes that were not previously possible. Trait approaches can help to test mechanistic hypotheses on the top‐down impacts of large herbivores on plant communities to reveal links between trophic rewilding and ecosystem processes and properties.
Synthesis . Given the rapid, much‐needed expansion of restoration and rewilding activities across the world, trait‐based ecology offers a pathway to generalisable predictions of the ecosystem impacts of rewilding, particularly in the context of both the unique landscape processes associated with rewilding (e.g. landscape scale spatiotemporal variability, dispersal) and of widely emerging novel ecosystems.
... Fire reduces grazing lawn success indirectly by creating green flushes in other areas which draw the grazers away from the lawns (Bond and Archibald 2003;Van Langevelde et al. 2003) and thus restricting the development and maintenance of lawns and perpetuating fire-driven systems. Increases in mineral concentration in the grass may result in grazing lawns that are herbivore-driven (Waldram et al. 2007;Archibald 2008;Cromsigt and Olff 2008;Novellie and Gaylard 2013;Hempson et al. 2014;Zwerts et al. 2015). In nutrient poor savannas with grasses of low nutritional value, herbivores may have poor body condition resulting in low levels of nutritional value in their milk and thus a negative effect on fecundity. ...
Nutrient poor savannas are often characterized by inedible or rarely palatable grasses, which generally provide poor nutrition for mammalian grazers. So-called grazing lawns, with short, stoloniferous edible grasses, could provide high-quality food for grazers, but these lawn grasses are rare in nutrient poor savannas. We tested whether we could use mineral addition to establish grazing lawns in a nutrient poor African savanna, in order to achieve a switch from tall, nutritionally poor to short, highly nutritional grass species. The key finding is that phosphorus and lime, nitrogen and nitrogen and lime supplementation resulted in shift from tall to short grasses within three years, with a higher overall nutrient concentration in the grass leaf, than without supplementation. When grazed, the cover of lawn grasses was higher compared to the other grasses when not grazed, demonstrating the role of grazers in maintaining and expanding lawn grass patches. We conclude that local fertilisation in nutrient poor savannas is a viable method of increasing mineral levels in the soil and grass leaf. We also concluded that grazing results in an increase in lawn grass cover and a combination of fertilisation and grazing can improve forage quality to ensure higher nutrient availability to herbivores.
... giant buffalo (Syncerus antiquus), would have facilitated habitat for other species by creating grazing lawns similar to Cape buffalo(Syncerus caffer) today (Brooke, 2021), especially in the high forage biomass areas associated with the floodplain woodlands during times of limited resources. In current landscapes, elephants facilitate habitat for smaller species by manipulating vegetation through breaking trees and creating pathways bringing forage into the reach of smaller browsers, whereas hippopotamus (Hippopotamus amphibius) and white rhinoceros (Ceratotherium simum) are capable of creating and maintaining short grass grazing lawns characterized by low biomass and high quality vegetation (Archibald, 2008;Cromsigt & Olff, 2008;Waldram et al., 2007;Hempson et al., 2015b). Humans using fire would also have facilitated habitat for other species by burning off dry grass and stimulating fresh green regrowth (Archibald & Bond, 2004;. ...
One of the primary goals of the palaeosciences is to produce robust understandings of palaeoecologies of extinct ecosystems. The time has arrived where such palaeoecologies can be significantly improved-agent-based models (ABMs) that synthesize our modern understandings of animal ecology with past conditions provide a unique opportunity for this. The Palaeo-Agulhas Plain (PAP), a now submerged landscape off the south coast of South Africa, formed a novel ecosystem during the lower sea levels of the Pleistocene. Here we provide a review of the utility of ABMs for understanding herbivores in prehistoric environments using the Paleoscape Model. The Paleoscape Model is fortunate to have features models of climate, geology and vegetation upon which we can understand how herbivores used the PAP environment. To incorporate aspects of herbivore behaviour and habitat suitability into the model requires analogies from extant systems. In addition to reconstructions of the availability of resources and associated risks, data on herbivore behaviour and physiology are imperative to our understanding of these systems. Behaviour, driven by changes in the environment, is interpreted by species, leading to selection of suitable habitats ultimately driving the herbivore's decisions within ABMs. Finally, we discuss herbivore integration into these models that can be used in numerous other scenarios (past, present and future).
... giant buffalo (Syncerus antiquus), would have facilitated habitat for other species by creating grazing lawns similar to Cape buffalo(Syncerus caffer) today (Brooke, 2021), especially in the high forage biomass areas associated with the floodplain woodlands during times of limited resources. In current landscapes, elephants facilitate habitat for smaller species by manipulating vegetation through breaking trees and creating pathways bringing forage into the reach of smaller browsers, whereas hippopotamus (Hippopotamus amphibius) and white rhinoceros (Ceratotherium simum) are capable of creating and maintaining short grass grazing lawns characterized by low biomass and high quality vegetation (Archibald, 2008;Cromsigt & Olff, 2008;Waldram et al., 2007;Hempson et al., 2015b). Humans using fire would also have facilitated habitat for other species by burning off dry grass and stimulating fresh green regrowth (Archibald & Bond, 2004;. ...
One of the primary goals of the palaeosciences is to produce robust understandings of palaeoecologies of extinct ecosystems. The time has arrived where such palaeoecologies can be significantly improved—agent-based models (ABMs) that synthesize our modern understandings of animal ecology with past conditions provide a unique opportunity for this. The Palaeo-Agulhas Plain (PAP), a now submerged landscape off the south coast of South Africa, formed a novel ecosystem during the lower sea levels of the Pleistocene. Here we provide a review of the utility of ABMs for understanding herbivores in prehistoric environments using the Paleoscape Model. The Paleoscape Model is fortunate to have features models of climate, geology and vegetation upon which we can understand how herbivores used the PAP environment. To incorporate aspects of herbivore behaviour and habitat suitability into the model requires analogies from extant systems. In addition to reconstructions of the availability of resources and associated risks, data on herbivore behaviour and physiology are imperative to our understanding of these systems. Behaviour, driven by changes in the environment, is interpreted by species, leading to selection of suitable habitats ultimately driving the herbivore’s decisions within ABMs. Finally, we discuss herbivore integration into these models that can be used in numerous other scenarios (past, present and future).
... Animals can inf luence fire regimes by modifying the amount, structure and condition of fuels in the landscape (Foster et al., 2020;Holdo et al., 2009). Megaherbivores (>1000 kg) such as white rhinoceros (Ceratotherium simum) create grazing lawns of short grass that inf luence the behaviours of other grazers and lead to smaller, more heterogeneous fires (Waldram et al., 2008). African forest elephants browse paths along forest edges that limit wildfire spread (Cardoso et al., 2020). ...
Ecosystem functions in a series of feedback loops that can change or maintain vegetation structure. Vegetation structure influences the ecological niche space available to animals, shaping many aspects of behaviour and reproduction. In turn, animals perform ecological functions that shape vegetation structure. However, most studies concerning three‐dimensional vegetation structure and animal ecology consider only a single direction of this relationship. Here, we review these separate lines of research and integrate them into a unified concept that describes a feedback mechanism. We also show how remote sensing and animal tracking technologies are now available at the global scale to describe feedback loops and their consequences for ecosystem functioning. An improved understanding of how animals interact with vegetation structure in feedback loops is needed to conserve ecosystems that face major disruptions in response to climate and land‐use change.
... For example, the presence of forest elephants (Loxodonta cyclotis) favors the emergence of fewer and larger trees with higher wood density (Berzaghi et al., 2019). White rhinos (Ceratotherium simum simum) help maintain short grass communities which result in smaller more patchy fires (Waldram et al., 2008), and dugongs (Dugong dugong), large aquatic grazers, can alter seagrass communities affecting carbon sequestration and storage (Scott et al., 2018). Theories have emerged that baleen whales may also act as ecosystem engineers by influencing the ocean carbon cycle on regional and large basin scales as part of the marine food web (Willis, 2014) even bringing the idea of 'carbon credits' into the debate (Hagger et al., 2022;Pearson et al., 2023). ...
Whales have been titled climate savers in the media with their recovery welcomed as a potential carbon solution. However, only a few studies were performed to date providing data or model outputs to support the hypothesis. Following an outline of the primary mechanisms by which baleen whales remove carbon from the atmosphere for eventual sequestration at regional and global scales, we conclude that the amount of carbon whales are potentially sequestering might be too little to meaningfully alter the course of climate change. This is in contrast to media perpetuating whales as climate engineers. Creating false hope in the ability of charismatic species to be climate engineers may act to further delay the urgent behavioral change needed to avert catastrophic climate change impacts, which can in turn have indirect consequences for the recovery of whale populations. Nevertheless, whales are important components of marine ecosystems, and any further investigation on existing gaps in their ecology will contribute to clarifying their contribution to the ocean carbon cycle, a major driver of the world’s climate. While whales are vital to the healthy functioning of marine ecosystems, overstating their ability to prevent or counterbalance anthropogenically induced changes in global carbon budget may unintentionally redirect attention from known, well-established methods of reducing greenhouse gases. Large scale protection of marine environments including the habitats of whales will build resilience and assist with natural carbon capture.
... The park was officially proclaimed as protected in 1898 with the intention of conserving mammals whose abundance and richness was threatened by anthropogenic activities and climate change [19][20][21]. Gradual decline in the number of grazers per unit area was attributed to poaching, predation, disease, climate change and culling during seasons where food resource is inadequate at the protected nature reserve [22][23][24][25]. Change in the number of grazers influences heterogeneity of landscapes, abundance, diversity and composition of plants, mammals, birds and arthropods [1,[26][27][28]. ...
Protected savannas are essential reserves for biological diversity, including endangered arthropod species, however, extreme grazing by mammals has cascading impacts on the communities and disrupts the functioning of these ecosystems globally. The current study assessed the abundance, species richness and composition of arthropods at the long-term grazing exclosures of Kruger National Park, South Africa. Pitfall traps and active searches were used to sample arthropods at the ungrazed, moderately, and heavily grazed exclosures. We found that Hymenoptera, Coleoptera, Diptera and Araneae were the most abundant orders of arthropods sampled. The abundance of multi-taxon, Diptera and Hymenoptera was significantly different between exclosures. In contrast, Coleoptera had high numbers of morphospecies compared to Hymenoptera, Araneae and Diptera. Species richness for multi-taxon, Diptera and Hymenoptera was significantly high at the heavily grazed compared to moderately grazed and ungrazed exclosures. Up to 22.2%, 41.2%, and 44.4% of the morphospecies were unique to the ungrazed, moderately and heavily grazed exclosures, respectively. A high proportion of morphospecies shared between exclosures were Coleoptera (41.0%) and Hymenoptera (38.5%) compared to Diptera and Araneae with less than 5% recorded across exclosures. Thus, morphospecies within the least abundant orders, namely Diptera and Araneae, were represented by singletons that were unique to particular exclosures compared to the most abundant arthropod orders (e.g., Coleoptera and Hymenoptera). We conclude that long-term mammal grazing enhances species richness and niche composition together with sparse and unique arthropods in the protected savannas. Therefore, managed grazing regimes can serve as a tool for maintaining the integrity of the protected savannas.
... Some of the factors to consider would be: (1) conservation status and rarity, especially if animals are endangered and threatened [112]; (2) economic value in terms of ecotourism potential and medicinal value could influence their perceived value [113]; (3) ecological value, such as their role in maintaining ecosystem health or providing ecosystem services. For example, white rhinoceros, in addition to being of high tourism value, are also facilitators, providing other grazing herbivores with improved grazing conditions [114]; (4) cultural significance can impact perceived value, for example, by being considered sacred or having an important role in traditional cultural practices [115]; and (5) local knowledge about mammal behaviour, ecology, and uses could influence their perceived value [116]. ...
The biodiversity of our planet is under threat, with approximately one million species expected to become extinct within decades. The reason: negative human actions, which include hunting, overfishing, pollution, and the conversion of land for urbanisation and agricultural purposes. Despite significant investment from charities and governments for activities that benefit nature, global wildlife populations continue to decline. Local wildlife guardians have historically played a critical role in global conservation efforts and have shown their ability to achieve sustainability at various levels. In 2021, COP26 recognised their contributions and pledged USD 1.7 billion per year; however this is a fraction of the global biodiversity budget available (between USD 124 billion and USD 143 billion annually) given they protect 80% of the planets biodiversity. This paper proposes a radical new solution based on “Interspecies Money”, where animals own their own money. Creating a digital twin for each species allows animals to dispense funds to their guardians for the services they provide. For example, a rhinoceros may release a payment to its guardian each time it is detected in a camera trap as long as it remains alive and well. To test the efficacy of this approach, 27 camera traps were deployed over a 400 km2 area in Welgevonden Game Reserve in Limpopo Province in South Africa. The motion-triggered camera traps were operational for ten months and, using deep learning, we managed to capture images of 12 distinct animal species. For each species, a makeshift bank account was set up and credited with GBP 100. Each time an animal was captured in a camera and successfully classified, 1 penny (an arbitrary amount—mechanisms still need to be developed to determine the real value of species) was transferred from the animal account to its associated guardian. The trial demonstrated that it is possible to achieve high animal detection accuracy across the 12 species with a sensitivity of 96.38%, specificity of 99.62%, precision of 87.14%, F1 score of 90.33%, and an accuracy of 99.31%. The successful detections facilitated the transfer of GBP 185.20 between animals and their associated guardians.
