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Invasive Plants and Water Resources in the Western Cape Province, South Africa: Modelling the Consequences of a Lack of Management
Journal of Applied Ecology
Abstract
1. The invasion of fynbos shrublands by woody weed species can reduce the water yield from catchment areas dramatically. We modelled the consequences of uncontrolled invasion on water yield using a geographical information system (Arc/Info). 2. Five important processes were recognized: the occurrence of fire; the spread and establishment of alien plants after fire; rainfall-to-run-off ratios; growth and changes in biomass between fires; and effects of these changes on streamflow. 3. The simulations of water yield were modelled with the Arc/Info GRID module using a 200 x 200-m grid. It was assumed that the interval between fires was 15 years and that proliferation and dispersal of alien plants took place only after fires. 4. Between fires, the model simulated the growth of the vegetation and its effects on streamflow, using relationships between rainfall and run-off, and run-off and above-ground biomass. 5. Results for the Kogelberg area in the Western Cape Province showed that alien plants invaded about 40% of the grid cells within 50 years. Cover of alien plants increased from an initial estimate of 2.4% to 62.4% after 100 years. 6. Invasion of catchment areas would result in an average decrease of 347 m3 of water per hectare per year over 100 years, resulting in average losses of more than 30% of the water supply to the city of Cape Town. In individual years, where large areas would be covered by mature trees, losses would be much greater. 7. In addition, invasion of fynbos by alien plants will cause the extinction of many plant species, increase the intensity of fires, destabilize catchment areas with resultant erosion and diminished water quality, and decrease the aesthetic appeal of mountain areas. 8. Control of alien weed species is necessary to avert the above impacts, and the costs of control operations could be justified by the savings achieved in maintaining adequate water run-off from stable catchments in the long term.
... Concerns about the impacts of alien plant invasions on streamflows were a key factor in the establishment of the Working for Water programme in October 1995 and in sustaining the programme since then (Le Maitre et al., 1996;Le Maitre et al., 2000;Van Wilgen et al., 1998). The streamflow reduction models used to estimate the flow reductions were based on long-term studies of the impacts of plantations on streamflows in catchments spread across South Africa compared with natural vegetation, particularly fynbos (Van Wyk, 1987;Van Lill et al., 1980;Bosch et al., 1980;Bosch and Von Gadow, 1990). ...
... The streamflow reduction models used to estimate the flow reductions were based on long-term studies of the impacts of plantations on streamflows in catchments spread across South Africa compared with natural vegetation, particularly fynbos (Van Wyk, 1987;Van Lill et al., 1980;Bosch et al., 1980;Bosch and Von Gadow, 1990). The invasions often involved the same or ecologically similar tree species as those in the plantation studies, strengthening the argument that the reductions caused by invasions could match those observed in plantation studies (Le Maitre et al., 1996;Le Maitre, 2004). Ongoing research into water use by individual plants and stands of invasive species (Everson et al., 2014;Dzikiti et al., 2013;Meijninger and Jarmain, 2014;Dye and Jarmain, 2004) has confirmed the original findings, and shown that invasions can have substantial impacts on streamflows (see review by Le Maitre et al., 2015). ...
... Each of the invaded units (polygons) was identified as being riparian or non-riparian, or one where groundwater could be accessed by plant root systems. This information was required for the estimation of the hydrological impacts as an indication of relative water availability (Le Maitre et al., 1996;Le Maitre et al., 1999. Where necessary, invaded polygons were sub-divided to define the riparian sections more accurately. ...
A key motivation for managing invasive alien plant (IAP) species is their impacts on streamflows, which, for the wetter half of South Africa, are about 970 m 3 •ha −1 •a −1 or 1 444 mill. m 3 •a −1 (2.9% of naturalised mean annual runoff), comparable to forest plantations. However, the implications of these reductions for the reliability of yields from large water supply systems are less well known. The impacts on yields from the WCWSS were modelled under three invasion scenarios: 'Baseline' invasions; increased invasions by 2045 under 'No management'; and under 'Effective control' (i.e. minimal invasions). Monthly streamflow reductions (SFRs) by invasions were simulated using the Pitman rainfall−runoff catchment model, with taxon-specific mean annual and low-flow SFR factors for dryland (upland) invasions and crop factors for riparian invasions. These streamflow reduction sequences were input into the WCWSS yield model and the model was run in stochastic mode for the three scenarios. The 98% assured total system yields were predicted to be ±580 million m 3 •a −1 under 'Effective control', compared with ±542 million m 3 •a −1 under 'Baseline' invasions and ±450 mill. m 3 •a −1 in 45 years' time with 'No management'. The 'Baseline' invasions already reduce the yield by 38 mill. m 3 •a −1 (two thirds of the capacity of the Wemmershoek Dam) and, in 45 years' time with no clearing, the reductions would increase to 130 mill. m 3 •a −1 (capacity of the Berg River Dam). Therefore IAP-related SFRs can have significant impacts on the yields of large, complex water supply systems. A key reason for this substantial impact on yields is that all the catchments in the WCWSS are invaded, and the invasions are increasing. Invasions also will cost more to clear in the future. So, the best option for all the water-users in the WCWSS is a combined effort to clear the catchments and protect their least expensive source of water.
... Concerns about the impacts of alien plant invasions on streamflows were a key factor in the establishment of the Working for Water programme in October 1995 and in sustaining the programme since then (Le Maitre et al., 1996;Le Maitre et al., 2000;Van Wilgen et al., 1998). The streamflow reduction models used to estimate the flow reductions were based on long-term studies of the impacts of plantations on streamflows in catchments spread across South Africa compared with natural vegetation, particularly fynbos (Van Wyk, 1987;Van Lill et al., 1980;Bosch et al., 1980;Bosch and Von Gadow, 1990). ...
... The streamflow reduction models used to estimate the flow reductions were based on long-term studies of the impacts of plantations on streamflows in catchments spread across South Africa compared with natural vegetation, particularly fynbos (Van Wyk, 1987;Van Lill et al., 1980;Bosch et al., 1980;Bosch and Von Gadow, 1990). The invasions often involved the same or ecologically similar tree species as those in the plantation studies, strengthening the argument that the reductions caused by invasions could match those observed in plantation studies (Le Maitre et al., 1996;Le Maitre, 2004). Ongoing research into water use by individual plants and stands of invasive species (Everson et al., 2014;Dzikiti et al., 2013;Meijninger and Jarmain, 2014;Dye and Jarmain, 2004) has confirmed the original findings, and shown that invasions can have substantial impacts on streamflows (see review by Le Maitre et al., 2015). ...
... Each of the invaded units (polygons) was identified as being riparian or non-riparian, or one where groundwater could be accessed by plant root systems. This information was required for the estimation of the hydrological impacts as an indication of relative water availability (Le Maitre et al., 1996;Le Maitre et al., 1999. Where necessary, invaded polygons were sub-divided to define the riparian sections more accurately. ...
A key motivation for managing invasive alien plant (IAP) species is their impacts on streamflows, which, for the wetter half of South Africa, are about 970 m3∙ha−1∙a−1 or 1 444 mill. m3∙a−1 (2.9% of naturalised mean annual runoff), comparable to forest plantations. However, the implications of these reductions for the reliability of yields from large water supply systems are less well known. The impacts on yields from the WCWSS were modelled under three invasion scenarios: ‘Baseline’ invasions; increased invasions by 2045 under ‘No management’; and under ‘Effective control’ (i.e. minimal invasions). Monthly streamflow reductions (SFRs) by invasions were simulated using the Pitman rainfall−runoff catchment model, with taxon-specific mean annual and low-flow SFR factors for dryland (upland) invasions and crop factors for riparian invasions. These streamflow reduction sequences were input into the WCWSS yield model and the model was run in stochastic mode for the three scenarios. The 98% assured total system yields were predicted to be ±580 million m3∙a−1 under ‘Effective control’, compared with ±542 million m3∙a−1 under ‘Baseline’ invasions and ±450 mill. m3∙a−1 in 45 years’ time with ‘No management’. The ‘Baseline’ invasions already reduce the yield by 38 mill. m3∙a−1 (two thirds of the capacity of the Wemmershoek Dam) and, in 45 years’ time with no clearing, the reductions would increase to 130 mill. m3∙a−1 (capacity of the Berg River Dam). Therefore IAP-related SFRs can have significant impacts on the yields of large, complex water supply systems. A key reason for this substantial impact on yields is that all the catchments in the WCWSS are invaded, and the invasions are increasing. Invasions also will cost more to clear in the future. So, the best option for all the water-users in the WCWSS is a combined effort to clear the catchments and protect their least expensive source of water.
... Water availability in many areas of South Africa has become a significant concern, and efforts to conserve water are increasingly shifting towards demand management (Turpie et al. 2008;Egoh et al. 2012;Nel et al. 2017;Shackleton et al. 2019f). Invasive alien trees use significantly more water than indigenous grasslands (Dye et al. 2001;Dye and Jarmain 2004;Everson et al. 2011;Le Maitre et al. 2015), thereby reducing surface run-off, streamflow, and subsequently water supply and security (Le Maitre et al. 1996Dzikiti et al. 2013;Preston et al. 2018). Awareness of the link between IAPs and water resources has increased considerably since the establishment of the Working for Water programme in the 1990s (Le Maitre et al. 1996Turpie et al. 2008;van Wilgen et al. 2012). ...
... Invasive alien trees use significantly more water than indigenous grasslands (Dye et al. 2001;Dye and Jarmain 2004;Everson et al. 2011;Le Maitre et al. 2015), thereby reducing surface run-off, streamflow, and subsequently water supply and security (Le Maitre et al. 1996Dzikiti et al. 2013;Preston et al. 2018). Awareness of the link between IAPs and water resources has increased considerably since the establishment of the Working for Water programme in the 1990s (Le Maitre et al. 1996Turpie et al. 2008;van Wilgen et al. 2012). This is likely to influence respondents' perceptions of IAPs either by shifting or solidifying current views. ...
Many alien tree species were introduced into grassland ecosystems in South Africa by the commercial forestry industry for paper and timber for furniture. Over decades some of these introduced species escaped into neighbouring farms and community land. Adult trees from these alien species now provide other ecosystem services, notably fuelwood. Depending on the spatio-temporal context, many of these species can also negatively affect ecosystem services. We collected interview data from commercial and communal farmers in the upper Umzimvubu catchment in South Africa to compare farmers' knowledge and perceptions of invasive wattle species invasion and their associated ecosystem services and disservices. Fuelwood and fencing poles were the most common uses of wattle by commercial (83%; 67%) and communal (99%; 49%) farmers. On the other hand, the reduction of grass cover and loss of grazing land were the most commonly mentioned negative impacts of wattles by commercial (83%; 75%) and communal (92%; 80%) farmers. Although both groups recognise the importance of wattles in providing ecosystem services, most communal farmers perceived wattles to have more negative effects than benefits. The findings demonstrate that both farmer groups highly depend on ecosystem services and are affected by disservices of wattles. However, while large-scale commercial households favour the presence of wattles in the landscape, communal households prefer complete removal of the wattles from the landscape. This may be due to lack of locally available alternative options or inability to replace or purchase ecosystem services affected by wattles from other sources or markets like commercial farmers. ARTICLE HISTORY
... Several studies have attempted to estimate the impacts of invasive alien trees on water supplies. The first study (Le Maitre et al. 1996) estimated that invasion of a 35,000 ha catchment by alien trees and shrubs would decrease water runoff by 10.6% on average over a 100-year period, resulting in substantial threats to the sustainable supply of water to the city of Cape Town. Studies using similar models and assumptions estimated that invasive alien trees reduced river flows by between 7.2 and 22.1% in four catchments ranging in size from 13,000 to 63,000 ha 1940, 1948, 1956, 1964, and 1972, and one was left unplanted as a control van Wyk (1987) Impact of bovine tuberculosis on buffalo (Syncerus caffer) ...
... There are already well-documented warnings in this regard arising from the South African experience. Scarce and vital water resources are being depleted in areas of relatively high rainfall (e.g. the catchments of Cape Town, invaded by alien trees and shrubs, Le Maitre et al. 1996), as well as in more arid areas where people are almost totally dependent on groundwater (e.g. in the case of invasions by Prosopis in arid regions, Dzikiti et al. 2017;Wise et al. 2012). The invasion of shrublands by alien trees can also change fire regimes, increasing the risks associated with wildfires (Kraaij et al. 2018), diminishing the water-retention capacity of catchments due to soil damage and erosion (van Wilgen and Scott 2001), and hastening the extinction of hundreds of endemic plant and animal species (Raimondo et al. 2009). ...
Compared to other facets of invasion science, the impacts of biological invasions have been understudied, but many studies have been published in the last decade. This paper reviews the growing body of evidence of impacts of invasions in South Africa. We classified information for individual species into ten ecological and four social categories of impact. We also reviewed studies that upscaled this information to larger spatial scales, as well as progress with assigning invasive species to impact severity categories. We identified 123 studies that documented the impacts of 71 invasive alien species, about 5 of the country's naturalized alien biota. The most frequently reported impact category was species interactions (changes to habitat suitability, pollination networks or seed dispersal mechanisms), followed by direct competition , changes to ecosystem functioning (hydrology or nutrient dynamics), hybridization and predation. Trees and shrubs accounted for more than half of the species studied, but there were examples from most other groups of plants and animals. The social consequences of invasions have been less well studied at the level of individual species. Most studies (72%) considered the impacts of a single species, based on data collected on \ 1 ha, and were completed in less than a year. Space-for-time substitution was widely used, but widespread collection of data from numerous small plots allowed for reporting impact over larger spatial scales. We also identified seven studies that either monitored impacts over longer periods (up to 40 years), or repeated surveys in the same area to assess change over time. Prominent landscape-scale impacts included reductions in water resources, the attrition of native biodiversity, reductions in rangeland productivity, predation of marine birds and freshwater fishes, and disease organisms affecting native mammals and trees. Nineteen studies at broader scales estimated substantial impacts on landscape-scale water yield, habitats and biodiversity, rangeland productivity, and the economic value of ecosystem services. Despite considerable progress, our understanding remains fragmentary. Impacts are expected to grow as invasions enter exponential phases of spread and densifi-cation and as the duration of invasions increases.
... Yet, some of these NNT may decrease other ecosystem services different from those intended to enhance. Harms caused by introduced non-native species are often related to the alteration of relevant ecosystem processes, such as primary production, nutrient or water cycles, or fire regimes (Corbin and D'Antonio, 2011;Le Maitre et al., 1996;Levine et al., 2003;Pejchar and Mooney, 2009;Vitousek and Walker, 1989), as well as the decline of local diversity (Gaertner et al., 2009;Vilà et al., 2011). ...
... The increased land water pools by Acacia found in this review contrasts with studies performed in South Africa, where the invasion of catchments by non-native woody plants (Acacias among them) lead to significant reductions of river flows (Le Maitre et al., 1996;Le Maitre et al., 2002). Our finding relied on seven case studies which showed higher infiltration rates, enhanced litter mass accumulation, higher water use efficiency or higher soil moisture in sites dominated by Acacia. ...
Tree taxa are often planted beyond their native range to increase the provision of some ecosystem services. Yet, they can disrupt ecosystem processes in their new ranges, causing changes in the provision of other services. Here we review the effects of five widespread tree taxa (Acacia, Ailanthus, Eucalyptus, Pinus and Robinia) on six regulating ecosystem services in areas where they are non-native. We conducted a literature search for pair-wise comparisons between sites dominated by any of the selected taxa and sites with native vegetation. An array of variables were used as indicators for each ecosystem service. Data were analysed using multi-level meta-analyses to compare effects of taxa on each ecosystem service, and effects of the same taxa across contexts. We compiled 857 case studies from 107 source papers. Several taxa tended to increase climate regulation, mostly Eucalyptus. Acacia decreased fire risk prevention. Robinia, Acacia and Ailanthus increased soil fertility, while Eucalyptus and Pinus, tended to decrease it. Soil formation was enhanced by Robinia and Ailanthus. Acacia promoted the increase of water in land pools, while Eucalyptus tended to decrease them. All effects show a large heterogeneity across case studies. Part of this heterogeneity could be attributed to gross climatic differences (i.e. biome), to species differences within each genus, to the structure of the recipient ecosystem, and/or to human management. Managers and policy-makers should consider the context-dependency and the potential effects of non-native trees on a wide range of services to ground their decisions. Our analyses also revealed important gaps of knowledge (e.g. on fire risk prevention, erosion control or water cycle regulation) and some potential publication bias. The methodology used here easily allows for future updates as new information will become available.
... To achieve this goal, clear objectives, strategies, adaptive planning, adequate resources and funding for long-term implementation are required (Esler et al., 2010;Foxcroft and McGeoch, 2011;van Wilgen et al., 2016a). Predictive models that consider ecological drivers such as fire, invasion rate, ecological impact and factors that increase uncertainty, such as clearing efficiency, can provide estimates of expected outcomes defined by particular sets of conservation objectives and resource allocations (Le Maitre et al., 1996;Higgins et al., 2000;Krug et al., 2010;Cheney et al., 2019). Prioritisation models for IAP management that attempt to account for multiple objectives and uncertainties have been developed for a number of applications and include water catchment areas (van Wilgen et al., 2007;Forsyth et al., 2012), protected area management (Forsyth and Le Maitre, 2011;van Wilgen et al., 2016a) and maximisation of economic cost-benefit ratios (Higgins et al., 1997;de Wit et al., 2001). ...
... Fig. 1; Cheney et al., 2019). The model simulates Acacia population size, age structure and area invaded, within each of the 809 management units, based on two key drivers of Acacia persistence, namely fire dynamics and plant population (growth and seedbank) dynamics (Le Maitre et al., 1996;Higgins et al., 2000;Krug et al., 2010). Starting population data for the model (year 0) were based on fine-scale data collected from a systematic survey in-field from 10,057 plots that uniformly covered all management units (Cheney et al., 2018). ...
Conservation managers are required to make decisions in complex and uncertain contexts. To strengthen the robustness of conservation decisions, several approaches have been proposed to facilitate stakeholder engagement in the setting of conservation objectives and priority actions. While such processes have led to the formulation of several invasive alien plant management strategies to achieve specific objectives, the long-term consequences and trade-offs inherent in these strategies have not been tested. The performance of five of these strategies over 50 years was tested in the protected area context using empirical data from Table Mountain National Park, South Africa. A simulation model based on data for invasive Acacia species in a fire-driven ecosystem, focused on the interaction between strategy performance and clearing efficacy in achieving a management goal or reducing Acacia density to below 1 plant per hectare. At near perfect levels of clearing efficacy, all strategies converged towards reaching the management goal, while at lower efficacy levels the strategies diverged in their ability to achieve desired outcomes. Despite working across the largest area, strategies that focussed on clearing low density invasions, maintained the least area in a maintenance state over time. In contrast, strategies that focussed on a mix of post-fire, low density areas and high altitude areas cleared less area annually, but maintained a much larger area in a maintenance state. At higher levels of efficacy, strategies that return to previously worked areas were more successful than a post-fire strategy. Strategies that focused solely on securing water, performed poorly in maintaining low overall density of aliens. However, the influence of efficacy was significant and substantial and a much larger difference in area reaching the management goal was achieved by varying efficacy than varying strategy. As such, improving quality of work and implementation will have a far greater effect than which areas are prioritized or how this prioritization is done. While acacias are likely to persist in the long-term, improving work quality coupled with correct strategy selection will ensure continued gains in the area under maintenance and improved return on investment over time.
... ecosystem disservices, EDS) (Shackleton et al., 2016), such as toxicity or allergenicity. Therefore, NNTs also create threats to people's livelihoods and human well-being, such as depletion of soil nutrients and water reserves (Castro-Díez et al., 2012;Le Maitre et al., 1996;Shackleton et al., 2014), increased fire hazard (D'Antonio, 2000;Gaertner, Le Maitre & Esler, 2017;Nagler et al., 2005), damage to infrastructure and archaeological remains (Booy et al., 2017;Celesti-Grapow & Blasi, 2004), or harm to human health (Nentwig, Mebs & Vilà, 2017;Schindler et al., 2015). These costs may be exacerbated when NNTs naturalize, and especially if they become invasive by spreading outside the areas where they were planted (Brundu & Richardson, 2016;Richardson & Rejmánek, 2011). ...
... We also note that maximizing some particular ecosystem services may not Biological Reviews (2019) always be beneficial for society or ecosystem functioning. For example, in the naturally infertile soils of some parts of Hawaii and the South African fynbos, the increase of soil nitrogen driven by the introduction of N-fixing NNTs is disrupting ecosystem functioning and altering several ecosystem services, such as soil fertility and water supply (Gaertner et al., 2011;Le Maitre et al., 1996;Vitousek & Walker, 1989). Thus, focussing environmental policies on ecosystem services may overlook the intrinsic value of nature and leave biodiversity under-protected (Dee et al., 2017;McCauley, 2006;Silvertown, 2015). ...
Non-native tree (NNT) species have been transported worldwide to create or enhance services that are fundamental for human well-being, such as timber provision, erosion control or ornamental value; yet NNTs can also produce undesired effects, such as fire proneness or pollen allergenicity. Despite the variety of effects that NNTs have on multiple ecosystem services, a global quantitative assessment of their costs and benefits is still lacking. Such information is critical for decision-making, management and sustainable exploitation of NNTs. We present here a global assessment of NNT effects on the three main categories of ecosystem services, including regulating (RES), provisioning (PES) and cultural services (CES), and on an ecosystem disservice (EDS), i.e. pollen allergenicity. By searching the scientific literature, country forestry reports, and social media, we compiled a global data set of 1683 case studies from over 125 NNT species, covering 44 countries, all continents but Antarctica, and seven biomes. Using different meta-analysis techniques, we found that, while NNTs increase most RES (e.g. climate regulation, soil erosion control, fertility and formation), they decrease PES (e.g. NNTs contribute less than native trees to global timber provision). Also, they have different effects on CES (e.g. increase aesthetic values but decrease scientific interest), and no effect on the EDS considered. NNT effects on each ecosystem (dis)service showed a strong context dependency, varying across NNT types, biomes and socioeconomic conditions. For instance, some RES are increased more by NNTs able to fix atmospheric nitrogen, and when the ecosystem is located in low-latitude biomes; some CES are increased more by NNTs in less-wealthy countries or in countries with higher gross domestic products. The effects of NNTs on several ecosystem (dis)services exhibited some synergies (e.g. among soil fertility, soil formation and climate regulation or between aesthetic values and pollen allergenicity), but also trade-offs (e.g. between fire regulation and soil erosion control). Our analyses provide a quantitative understanding of the complex synergies, trade-offs and context dependencies involved for the effects of NNTs that is essential for attaining a sustained provision of ecosystem services.
... The model simulates Acacia population size, age structure and area invaded within each management unit. The model's purpose is to estimate the potential future outcomes of the alien plant control programme by varying clearing efficacy (effective permanent removal of alien plants) in relation to two drivers of Acacia persistence, namely, ecosystem processes (fire) and plant population dynamics (age, density dependence and seedbank dynamics) (Le Maitre et al. 1996;Krug et al. 2010). Twelve model scenarios were simulated based on the current levels of Acacia abundance as determined by fine scale population data (Cheney et al. 2018), historic fire records spanning 35 years (Forsyth and van Wilgen, 2008), and 20 years of alien plant control history for TMNP (van Wilgen et al. 2016a). ...
... Previous models making use of high clearing efficacy parameters have shown a significant reduction in Acacia invasion within 20 years Le Maitre et al. 1996). Our models produced similar results at maximum efficiency (Fig. 4). ...
In many protected areas in South Africa, invasive Australian Acacia species pose on-going management challenges, perpetuating high long-term management costs. Due to limited availability of resources, conservation actions need to be prioritised within and across Protected Areas (PA). We draw on comprehensive datasets spanning over 20 years from the Table Mountain National Park to model long-term outcomes of clearing Acacia species at different levels of management clearing efficacy. We test a 50 year outlook based on current and 38 incremental levels of management efficacy, ranging from 5 to 100%, to assess under which scenarios a management goal of reducing Acacia density to below 1 plant per hectare for the 22,671 ha protected area is achieved. With the current clearing resources and maximum clearing efficacy (100% control), it would take between 32 and 42 years to attain the management goal. The modelling revealed two main drivers of Acacia persistence. Firstly, germination of seeds added to the seedbank from standing plants made a significantly larger contribution to future clearing requirements than fire stimulated seed germination or the existing (pre-management) seedbank. Secondly the relationship between the number of hectares and management units that could be treated and the efficacy of the treatment was non-linear. When clearing efficacy was decreased from 100% to the current project minimum target of 80% efficacy, the goal was not achieved in all areas, but the area that reached a density of <1 plant per hectare was significantly reduced to 53% of the PA for the simulated 50 years. Results emphasize the need to differentiate between increasing financial resources and increasing efficacy. While increasing financial resources allows for increased effort, this is of little value for Acacia management in the absence of an increase in clearing efficacy, as low quality implementation perpetuates the need for large budgets over time. Conversely, improving efficacy allows for decreased budget requirements over time, allowing fund re-direction to additional areas of alien species management such as the early detection and rapid control of newly introduced species.
... Argentina and Australia have both reported Tamarix invasions (Shafroth and Briggs, 2008;Gryphon et al., 1989). According to studies conducted in South Africa on the effects of invasive foreign tree species, stream flows have decreased by 4.7 to 13.0 percent (Dye, 1996;Le Maitre et al., 1996;Prinsloo and Scott, 1999;Le Maitre et al., 2000). ...
... Grasslands are the most primitive evolving systems of diverse plant communities (Little, Hockey & Jansen 2015). South African grasslands are being increasingly degraded through the increasing influence of overgrazing (Neke & Du Plessis 2004;O'Connor 1985), extensive and frequent burning (Uys, Bond & Everson 2004), plantation forestry (Lipsey & Hockey 2010) and invasion by alien plant species (Le Maitre et al. 1996). It is estimated that 60% of the grassland biome has been permanently transformed, while as little as 15% remains as natural grassland with only 2% formally conserved in South Africa (Carbutt et al. 2011;Macdonald 1989). ...
It is well known that fire is a common driver in many biomes and it plays a vital role in maintaining ecosystem functioning in many South African biomes. This ecosystem process is an important determinant of plant community composition and diversity, and can result in changes in structural composition and ecosystem functioning. The main objectives of this study are to determine the influence of fire on grass species richness, diversity and composition in Mountain Zebra National Park. Using satellite imagery, the park’s fire history was determined between 2000 and 2020. Eighty plots (approximately 20 m × 20 m; 100 m apart) were laid out purposively across different fire regimes. There was no significant difference in both species richness and diversity in burned and unburned sites. However, there was a difference in species composition between burned and unburned sites and between different fire frequencies. The unburned site had higher moribund material and unpalatable grasses compared to the burned area.Conservation implications: The results of this study will help in the completion of the fire management plan for the park which will enable conservation managers to make better decisions with regard to fire management in mountainous grassland at Mountain Zebra National Park. Consequently, this will lead to improved veld condition and vegetation structure.
... This study revealed that both endemic and invasive vegetation potentially rely on groundwater within the catchment. Invasive GDV threatens the endemic GDV as it can out-compete the endemic GDV and is more resilient to decreasing groundwater levels (Le Maitre et al., 1996;N. Jovanovic et al., 2013;Rouget et al., 2003;van Wilgen et al., 2008). ...
Groundwater dependent vegetation (GDV) is increasingly threatened by the transformation of the natural environment. An understanding of the nature of GDV at the appropriate scale helps environmental managers make suitable decisions. This study assesses the potential for mapping the distribution of GDV within the Heuningnes Catchment using multispectral remotely sensed data (i.e., Landsat 8 (L8) and Sentinel 2 (S2)), the derived vegetation indices (Normalised Difference Vegetation Index (NDVI) and the Soil-Adjusted Vegetation Index (SAVI)) and in-situ data. The GDV distribution maps were produced by integrating vegetation productivity, landcover, and topographic layers as GDV indicators. The findings of the study revealed that the spectral indices had a significant influence on the sensor’s GDV classification performance. Specifically, the S2-derived SAVI mapped the GDV areas with the highest overall accuracy (97%), followed by the S2-derived NDVI, with an accuracy of 95%. Comparatively, the L8(NDVI) GDV map was achieved with an overall accuracy of 92% and the L8(SAVI) map had an overall accuracy of 96%. The estimated coverage of potential GDV within the catchment ranges between 2.34 and 2.60%. This work demonstrated the capabilities of a combined remote sensing and GIS methodological framework, which can improve our knowledge on GDV.
... In California rangelands, the growth of an unpalatable invasive species yellow starthistle (Centaurea solstitialis) has been found to reduce forage availability and quality, thus causing the decline of livestock production and resulting in significant economic losses (Eagle et al. 2007). Likewise, invasive species may also have negative impacts on water regulation (Le Maitre et al. 1996). For example, in South Africa, increased invasions have caused a significant impact on streamflows throughout the Western Cape Water Supply System (Le Maitre et al. 2019), threatening the catchment areas with erosion, and have degraded the water quality in catchment areas (Enright 2000). ...
... In California rangelands, the growth of an unpalatable invasive species yellow starthistle (Centaurea solstitialis) has been found to reduce forage availability and quality, thus causing the decline of livestock production and resulting in significant economic losses (Eagle et al. 2007). Likewise, invasive species may also have negative impacts on water regulation (Le Maitre et al. 1996). For example, in South Africa, increased invasions have caused a significant impact on streamflows throughout the Western Cape Water Supply System (Le Maitre et al. 2019), threatening the catchment areas with erosion, and have degraded the water quality in catchment areas (Enright 2000). ...
The invasion of alien species manipulates the structure, function, and composition of the recipient ecosystem causing ecological, economic, and social impacts. However, these impacts can be positive or negative, depending on the effect and context of the invasion. In some cases, invasions enhance primary productivity of the ecosystem and increase species richness. On the other hand, in the majority of cases, the invasive species displace native species, adversely impacting native ecosystem and jeopardizing natural resources. The outcome of the impacts is based on several factors, such as mode of introduction, type of invasive species, condition of the invaded habitat, and characteristics of native species. For instance, specialist native species are predicted to suffer adverse effects, while generalists may flourish even when invasive species are abundant. There has been considerable debate in recent times about whether claims of severe impacts of invasive species are exaggerated and whether efforts to manage them are unnecessary or even harmful, and some unintended consequences of invasive species management have been documented. Regardless of the lack of consensus on the impacts of invasive species, they are posing a measurable cost to society. Invasive species severely affect agriculture, fisheries, tourism, forestry, and property values. Countries that rely on agriculture with small landholders are the most vulnerable to the invasion of exotic species. The rate of spread of invasive species is currently surging due to increased travel, trade, and transport in combination with climate change. Accurate and comprehensive information on economic and environmental impacts of invasive species is seriously lacking, and more research is needed to develop management strategies based on the impacts of invasive species.KeywordsAgricultureBiodiversityEcosystem servicesFisheriesForestryLivelihoods
... In California rangelands, the growth of an unpalatable invasive species yellow starthistle (Centaurea solstitialis) has been found to reduce forage availability and quality, thus causing the decline of livestock production and resulting in significant economic losses (Eagle et al. 2007). Likewise, invasive species may also have negative impacts on water regulation (Le Maitre et al. 1996). For example, in South Africa, increased invasions have caused a significant impact on streamflows throughout the Western Cape Water Supply System (Le Maitre et al. 2019), threatening the catchment areas with erosion, and have degraded the water quality in catchment areas (Enright 2000). ...
Humans have exchanged plant species beyond their native borders since millennia. The pathways of exchange and their relative importance have differed among regions, times and species. Here, we review the temporal developments of pathways of alien plant species introductions and how these relate to trends in alien plant species richness at a global scale. Although the rate of exchange of alien plants has grown steadily over time, significant advancements in human technological progress initiated new bursts of acceleration in global spread. Examples include the discovery of new seaways around 1500, the start of modern industrialisation in the early nineteenth century and the rise of global trade and human prosperity after World War II. Apart from a continuous intensification, the relative importance of pathways remained surprisingly stable. During the last 500 years, the introduction of plant species for cultivation represents the dominating pathway and was associated with more than half of all introductions. Although the relationship between horticulture and the occurrence of alien plants is often difficult to prove, the huge number of plants cultivated in the world makes it likely that, in the future, many introductions will continue to originate from private or public gardens. Indeed, horticulture remains the only introduction pathway which, up to now, has increased in relative importance among all pathways globally. Despite the rising awareness of the issues of introducing new alien species, the current socio-economic developments indicate that we have to expect many more alien plant species to come in the future.KeywordsBiological invasionsGlobalisationHistoricLong termNeophytesTime seriesWeeds
... In California rangelands, the growth of an unpalatable invasive species yellow starthistle (Centaurea solstitialis) has been found to reduce forage availability and quality, thus causing the decline of livestock production and resulting in significant economic losses (Eagle et al. 2007). Likewise, invasive species may also have negative impacts on water regulation (Le Maitre et al. 1996). For example, in South Africa, increased invasions have caused a significant impact on streamflows throughout the Western Cape Water Supply System (Le Maitre et al. 2019), threatening the catchment areas with erosion, and have degraded the water quality in catchment areas (Enright 2000). ...
Due to extreme climate and limited accessibility, mountains are marked by low human population density and relatively little direct human interference. However, the recent anthropogenic footprint in terms of climate change, land-use changes, infrastructure developments, and increased global connectivity have made these pristine ecoregions more vulnerable to plant invasions. Mountain regions are undergoing rapid socioeconomic transformation, causing increased disturbances associated with infrastructure development for transportation and tourism, changing the land use and land cover of these fragile landscapes. Climate change has emerged as an important factor that has the potential to accelerate the process of biological invasion in the mountains. Despite a large number of studies on mountain plant invasions, with some mountain regions being relatively well studied (e.g., European Alps) than others (e.g., Mountains of Central Asia), there is still a lack of information on the impacts of invasive alien plant species on these mountain communities. In this chapter, we review studies related to plant invasions in the mountain regions and discuss their drivers, pathways, patterns, and impacts. We also discuss the influence of climate change on plant invasions and finally discuss their management options. We anticipate the importance of future research on mountain ecosystems, including documentation of invasion patterns at varying spatial scales, and suggest further studies which could be useful in the management of invasive alien plant species.KeywordsClimate changeDisturbanceDriversMountain ecosystemPlant invasion
... In California rangelands, the growth of an unpalatable invasive species yellow starthistle (Centaurea solstitialis) has been found to reduce forage availability and quality, thus causing the decline of livestock production and resulting in significant economic losses (Eagle et al. 2007). Likewise, invasive species may also have negative impacts on water regulation (Le Maitre et al. 1996). For example, in South Africa, increased invasions have caused a significant impact on streamflows throughout the Western Cape Water Supply System (Le Maitre et al. 2019), threatening the catchment areas with erosion, and have degraded the water quality in catchment areas (Enright 2000). ...
The data available on the extent of global plant invasion shows a sharp increase in cases and associated costs over the last several decades. Indeed, most of the mixing of the planet’s flora due to human agency has occurred in the last 200 years. As in the case of rapidly emerging human pandemics that demand timely action, there have been urgent calls to stem the tide of plant invasions and prevent further spread and associated environmental and socioeconomic impacts. However, the response to most actual and potential plant invasions is far from simple. Naturalized plants have a broad range of impacts, such that a response specific to the particular plant species and habitat is often advisable, along with a meaningful dialog among stakeholders. Given the massive scale in changes of the flora in various regions, many naturalized species with minimal impacts are best left alone, whereas other naturalized species that have massive impacts warrant management to prevent further, often irreversible, effects on ecosystems. There exists a considerable array of invasive plants in this category, most of which are truly global, distributed on multiple continents. Of these high-impact invasive plant species, 37 are on the list of the International Union for Conservation of Nature (IUCN) 100 worst invasive alien species. Most of these high-impact species continue to spread in their non-native ranges, including sensitive island and mountain habitats. They also cause a range of socioeconomic impacts on agriculture, forestry, transportation, infrastructure, and cultural values. If current trends in plant invasions continue and are exacerbated by increasing global trade and climate change, many challenges lie ahead. We cannot turn back the clock to recover natural habitats free of invasive plants in most cases, but there are still ways of promoting ecosystem health through reducing populations of high-impact invasive plants and promoting holistic approaches to planet healing.KeywordsBiosurveillanceClimate changeGlobalizationInvasive plant costsIsland invasionsPlanet of weedsPlant invasion
... With wind dispersal, seeds often 'escape' from deliberate plantings and these wilding conifers have turned into invasive populations across many parts of Australasia, South America and southern Africa (Nuñez et al. 2017). Such trees then create a range of negative impacts, including depletion of soil nutrients and water reserves, increasing fire risk, reduction in landscape values and impacts on native ecosystems and species (Le Maitre et al. 1996;Richardson and Rejmánek 2011;Castro-Díez et al. 2019). Thus, there are substantial negative costs to be mitigated from industries that simultaneously generate significant proportions of nations' GDP. ...
In addition to being a major threat to biodiversity and ecosystem functioning, biological invasions also have profound impacts on economies and human wellbeing. However, the threats posed by invasive species often do not receive adequate attention and lack targeted management. In part, this may result from different or even ambivalent perceptions of invasive species which have a dual effect for stakeholders—being simultaneously a benefit and a burden. For these species, literature that synthesizes best practice is very limited, and analyses providing a comprehensive understanding of their economics are generally lacking. This has resulted in a critical gap in our understanding of the underlying trade-offs surrounding management efforts and approaches. Here, we explore qualitative trends in the literature for invasive species with dual effects, drawing from both the recently compiled InvaCost database and international case studies. The few invasive species with dual roles in InvaCost provide evidence for a temporal increase in reporting of costs, but with benefits relatively sporadically reported alongside costs. We discuss methods, management, assessment and policy frameworks dedicated to these species, along with lessons learned, complexities and persisting knowledge gaps. Our analysis points at the need to enhance scientific understanding of those species through inter- and cross-disciplinary efforts that can help advance their management.
... Furthermore, fire breaks and roads can allow desiccating winds to enter the forest canopy and dry out the understory (Brando et al. 2014), which may exacerbate the severity and extent to which forest margins would burn when occurring adjacent to plantations. Fire intensity and fire severity are positively associated with fuel load (Brooks et al. 2004;Keeley 2009) and conversion of fynbos shrublands to plantations of pine trees increases fuel loads from 3 to 4 t ha −1 to 20 t ha −1 (Le Maitre et al. 1996). Other fuel traits that differ between fynbos and pine plantations that may affect (increase or decrease) fire severity include the density, dis-tribution, moisture and chemical contents of fuels (Msweli et al. 2020). ...
Recently two large wildfires (around the towns of Knysna in 2017 and George in 2018) jointly burnt over 80 000 ha in the southern Cape, South Africa. Here, patches of closed-canopy Afrotemperate forest occur within a matrix of fire-prone (native) fynbos shrublands or adjacent to commercial plantations of invasive alien Pinus trees (a transformed state). We compared the distances that fire penetrated into forest margins adjacent to fynbos to those adjacent to plantations. Furthermore, we used a satellite-derived index of fire severity, the differenced Normalised Burn Ratio (dNBR), to compare fire severity in forest margins adjacent to fynbos to those adjacent to plantations. Results were inconsistent between the two fires. In the Knysna fire, no significant difference was noted in fire penetration into forest, while forest margins adjacent to plantations burnt at significantly lower severity than those adjacent to fynbos. In the George fire, penetration into and fire severity in forest margins adjacent to plantations were significantly greater than in those adjacent to fynbos. Not only were fire severity and penetration in forest margins with plantations adjacent dissimilar between the George and Knysna fires, but variability in fire severity was greater in forest margins with plantation adjacent than in those with fynbos adjacent. Our study provides evidence that fire severity in forest margins is associated with the adjacent vegetation type and that plantations potentially expose forests to greater variability in fire severity and extent than the forest may experience under natural conditions. Other important factors that may affect the severity and extent of burn in forest margins are forest patch size and topographical position, the nature of the ecotone between forest and the adjacent vegetation, and the fuel load and structure of the adjacent vegetation which varies considerably in relation to stand age and management practices in plantations.
... The limited ability to integrate the remaining species into a land cover class was too low for the spatial scale of the analysis and the three species chosen constituted a large proportion (82%) of the total condensed area of IAPs in the catchment. , 1996, 2000Enright, 2000;van Wilgen, 2010;Preston et al., 2018). Their review suggested that rates ranged from 7.4-15.6%, ...
This study forms part of the Natural Capital Accounting and Valuation of Ecosystem Services (NCAVES) project and builds on the compilation of pilot physical and monetary ecosystem services accounts for KwaZulu-Natal for 2005-2011. The analysis demonstrates the utility of ecosystem accounts – consistent with the System of Environmental Economic Accounting – Ecosystem Accounting (SEEA EA) framework – to inform policymaking. The study investigates the economic case for ecosystem management and restoration interventions in the Thukela river basin over the period 2021-2030 to achieve or exceed land degradation neutrality relative to a 2015 baseline. This study weighs the benefits of ecosystem restoration – in terms of the monetary value of improved provision of selected ecosystem services against the costs of interventions.
... Second, greater aboveground C sequestration is associated with increased water use and consequently lower water yield in catchments. Global studies show afforestation of grasslands or shrublands reduces streamflow and runoff by 40-75% (Farley et al. 2005;Jackson et al. 2005), which can restrict water availability to urban areas (Pejchar and Mooney 2009) and exacerbate problems of surface and groundwater availability in dry regions (Le Maitre et al. 1996Maitre et al. , 2000. In addition, decreased soil organic matter beneath invasive pines can reduce soil water retention relative to native grasslands (Farley et al. 2004). ...
Intentionally allowing or promoting invasion by non‐native trees into areas characterized by treeless vegetation could contribute to climate‐change mitigation by increasing carbon (C) sequestration. In some areas of the world, incentives exist to retain invasive non‐native trees in natural systems as a mechanism for increasing ecosystem C storage and reducing atmospheric carbon dioxide levels. Although this novel opportunity for C sequestration holds appeal, such an approach is problematic for several reasons: (1) invasive trees do not always increase net C sequestration due to greater occurrence of fire or reduced soil C; (2) lower albedo in invaded areas can increase absorption of solar radiation, thereby offsetting potential C sequestration; and (3) tree invasions often also have negative effects on biodiversity, economic opportunities, and water yield. Such drawbacks are sufficient to raise doubts about the widespread use of non‐native tree invasions in treeless areas as a tool to ameliorate climate change.
... Past research shows that shifts in vegetation life form, such as woody encroachment of arid landscapes or alteration of tropical forested landscapes to exotic grass pastures, incur dramatic hydrological shifts (Le Maitre et al. 1996;Bruijnzeel 2004;Huxman et al. 2005;Bonell et al. 2010;Muñoz-Villers and McDonnell 2012;Vasquez-Valderrama et al. 2020). While it may be more challenging to detect ecohydrological disruptions of within-system invasions (e.g. ...
Watershed degradation due to invasion threatens downstream water flows and associated ecosystem services. While this topic has been studied across landscapes that have undergone invasive-driven state changes (e.g., native forest to invaded grassland), it is less well understood in ecosystems experiencing within-system invasion (e.g. native forest to invaded forest). To address this subject, we conducted an integrated ecological and ecohydrological study in tropical forests impacted by invasive plants and animals. We measured soil infiltration capacity in multiple fenced (i.e., ungulate-free)/unfenced and native/invaded forest site pairs along moisture and substrate age gradients across Hawaii to explore the effects of invasion on hydrological processes within tropical forests. We also characterized forest composition, structure and soil characteristics at these sites to assess the direct and vegetation-mediated impacts of invasive species on infiltration capacity. Our models show that invasive ungulates negatively affect soil infiltration capacity consistently across the wide moisture and substrate age gradients considered. Additionally, several soil characteristics known to be affected by invasive ungulates were associated with local infiltration rates, indicating that the long-term secondary effects of high ungulate densities in tropical forests may be stronger than effects observed in this study. The effect of invasive plants on infiltration was complex and likely to depend on their physiognomy within existing forest community structure. These results provide clear evidence for managers that invasive ungulate control efforts can improve ecohydrological function of mesic and wet forest systems critical to protecting downstream and nearshore resources and maintaining groundwater recharge.
... The experiment conclusively demonstrated that afforestation of fynbos significantly reduced streamflow (Scott et al., 2000;van der Zel & Kruger, 1975; van Wyk, 1987;Wicht, 1967), and informed estimates of the impacts of invasive alien plants on water resources across South Africa (Le Maitre et al., 1996, 2016. These estimates have guided policy relating to invasive species and forestry, and prompted programmes to protect and restore catchments for water security (e.g., Stafford et al., 2019;van Wilgen et al., 1998). ...
The Jonkershoek Forestry Research Station was established in the Mediterranean climate region of South Africa in 1935 to implement a multiple catchment experiment to determine the effects of afforestation on water yield. The experiment consists of six neighbouring catchments previously supporting indigenous fynbos shrublands, five of which were sequentially afforested with Pinus radiata plantations every 8 years from 1940 to 1980 and one kept as the control. They conclusively demonstrated a significant impact of afforestation on streamflow. The treatment catchments have seen subsequent plantation rotations since 1980 and rainfall and streamflow observations have been continued to date. Here we describe the site, experimental design, rainfall and streamflow records, instrumentation, and how to access the data. We also provide details of recently installed instrumentation, including full weather stations, fog gauges, and an eddy covariance flux tower. The Jonkershoek catchment experiment was the core of a globally significant interdisciplinary research programme (1935 ‐ 1992) that shaped most environmental policies and practices relating to biodiversity, forestry, fire and water in South Africa and beyond. The South African Environmental Observation Network (SAEON) inherited the experiment in 2010 and is maintaining it as a long‐term eco‐hydrological research platform and global change observatory.
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... The avoided emissions of not burning biomass in fires are analyzed for the biomass component of BIC in the bio-based material scenario. In nature, in South Africa, circa every 15 years the IAP burn due to wild fires (Le Maitre et al., 1996;van Wilgen, 1996). It needs to be noted that this parameter directly influences the carbon credit calculations. ...
Today's cities are ever-growing, especially in the Global South, inducing massive construction activity. To satisfy these needs we need feasible and environmentally sustainable construction materials, the use of local solutions and, if possible, to enable synergies between sectors for maximum environmental benefit.
In South Africa and beyond, invasive alien plants are threatening the indigenous ecosystem while exacerbating water security by affecting water surface runoff and fueling wildfires that release carbon to the atmosphere. The literature suggests that bio-based construction materials can turn buildings into carbon pools. However, the dynamics of using bio-based materials at the urban scale are not yet well known. This paper tests a new type of non-structural bio-concrete, using invasive alien wood chips as a substitute for sand and gravel as aggregates, for future residential construction in Cape Town, comparing this new material to conventional and to earth-based materials, and benchmarking different policy scenarios. Firstly, the material is optimized within technical possibilities achieving the capture of 897 kg of CO2 equivalents per m³. Secondly, a reverse-engineered approach is employed to uncover the limitations of the material. Additionally, C02 emissions from cradle to gate and additional land and water use benefits are analyzed, considering spatial dynamics for transportation impacts.
The optimized mix design using invasive alien plants as an alternative resource, combined with a policy that promotes multi-story buildings, offers great potential to achieve near carbon neutral cities, clearing land of invasive alien plants and thus saving annual water surface runoff.
... Como se sabe las invasiones biológicas conllevan a profundos cambios en el funcionamiento de los ecosistemas, las mismas afectan a diversos servicios ecosistémicos, en algunas ocasiones, ocasionando importantes pérdidas económicas (Mack et al. 2000;Charles & Dukes, 2007). Particularmente, las invasiones por especies leñosas causan alteraciones en funciones ecosistémicas, como el ciclado del agua, ciclado de los nutrientes y regímenes de incendios, por lo que se lo ha considerado como un tema de suma importancia en nuestro territorio (Le Maitre et al. 1996;Farley et al. 2005). ...
Las invasiones biológicas constituyen un problema ambiental global del cual los sistemas montañosos no están exentos. El centro de Argentina, experimenta una creciente invasión por leñosas exóticas ornitócoras. Si bien la mayor riqueza de especies invasoras se encuentra en las partes bajas, C. franchetii ha colonizado el piso superior de las Sierras (~2000 msnm). Se ha sugerido que la dispersión ornitócora juega un rol fundamental para la expansión de esta especie en la región. La invasión de C. franchetii en las Sierras de Córdoba conforma en consecuencia un buen sistema de estudio para evaluar la influencia de gradientes ambientales y la variación asociada de los ensambles de mutualistas, sobre la efectividad de dispersión de plantas invasoras ornitócoras. Para evaluar dicha relación, se caracterizaron mediante puntos de conteo de radio fijo los ensambles de aves en tres sitios altitudinales de las Sierras Grandes de Córdoba (700, 1100 y 1800 msnm) representativos del rango altitudinal actual de C. franchetii. Los índices de diversidad alfa mostraron un patrón de decrecimiento de la riqueza de aves en general y frugívoras en particular. Además la diversidad beta y los análisis SIMPER y PERMANOVA a una vía mostraron disimilitudes entre dichos ensambles de aves en general y frugívoras en particular conforme se ascendía a lo largo del gradiente estudiado. Para evaluar el consumo de frutos de C. franchetii en el gradiente altitudinal e identificar qué variables lo explicaran, se cuantificaron eventos de frugivoría en 15 arbustos focales por altitud y se registró la abundancia e identidad de aves frugívoras (clasificándolas en grupos funcionales). Comparaciones exactas de Fisher mostraron que el consumo proporcional por dispersores legítimos aumentó con la altitud, a pesar que la riqueza de dispersores disminuyó (una sola especie a 1800 msnm). Un GLM inflado en ceros indicó que el consumo de frutos por dispersores legítimos se relacionó en forma directa con la abundancia de frugívoros y con la altitud, pero no así con la riqueza de dispersores legítimos. El mayor consumo por dispersores tanto proporcional como por planta focal se observó en el sitio de mayor altitud, donde sólo estuvo presente el Zorzal Chiguanco. Esto sugiere, que la riqueza de dispersores no determinaría una elevada efectividad de dispersión, sino que el factor determinante sería la presencia de una especie de ave generalista y abundante. Finalmente, debido que C. franchetii comparte el ensamble de frugívoros con otras exóticas presentes en sitios más bajos, y dado que las interacciones mutualistas no serían una limitante para su dispersión hacia sitios elevados, se sugiere que no habría limitaciones en cuanto a la dispersión para la expansión altitudinal del conjunto de exóticas ornitócoras de las sierras de Córdoba.
... Os ecossistemas mais frequentemente invadidos são savanas úmidas, vegetações arbustivas ou campos graminosos (Richardson, 1998;Zanchetta & Diniz, 2006), embora 8% dos casos de invasão por Pinus registrados em diferentes regiões do mundo por Richardson e Bond (1991) tenham sido em ecossistemas florestais. Ao invadir ecossistemas naturais, em curto espaço de tempo as árvores de Pinus passam a exercer forte impacto, ocasionando perdas consideráveis de biodiversidade (Abreu & Durigan 2011) e prejuízos para a oferta de recursos hídricos (Le Maitre et al., 1996). ...
... Os ecossistemas mais frequentemente invadidos são savanas úmidas, vegetações arbustivas ou campos graminosos (Richardson, 1998;Zanchetta & Diniz, 2006), embora 8% dos casos de invasão por Pinus registrados em diferentes regiões do mundo por Richardson e Bond (1991) tenham sido em ecossistemas florestais. Ao invadir ecossistemas naturais, em curto espaço de tempo as árvores de Pinus passam a exercer forte impacto, ocasionando perdas consideráveis de biodiversidade (Abreu & Durigan 2011) e prejuízos para a oferta de recursos hídricos (Le Maitre et al., 1996). ...
O manual reúne resultados de pesquisas do Instituto Florestal em parceria com outras instituição visando diagnosticar e compreender os processos de invasão de Pinus spp. e buscar soluções para o problema por meio de experimentação de técnicas de controle da invasão e restauração dos ecossistemas por ela prejudicados.
... Invasive alien plants have become a dominant feature in the catchments that supply Cape Town with water. These plants use signifi cantly more water than the indigenous vegetation, and thereby decrease surface run-off and ultimately water supply and security (Le Maitre et al. 1996 ). The Working for Water program was established in 1995 as a direct response to the loss of this critical resource (Van Wilgen et al. 1998 ) (see Chap. 24 ). ...
... condensed to their equivalent 100% density within a sub-catchment (for a definition of density categories, see Box 1, P26). 20 For example, a sub-catchment may have widespread coverage of invasive plants, but at a low density. The influence of plants in such a catchment will be potentially much lower than in a catchment where invasive alien plants occur at a high density particularly when these woody species establish themselves in riparian zones. ...
... An early South African example is provided by Higgins et al. (1997), who estimated that ecosystem services arising from a hypothetical 4 km 2 area of mountain fynbos would be worth US$3 million with no management of invasive species, compared to US $50 million with effective alien plant management. Other studies followed (see Le Maitre et al. 2011 for the most recent comprehensive review), but it was the prediction that alien plant invasions would lead to substantial reductions in water runoff from catchment areas (Le Maitre et al. 1996) that provided the economic motivation to initiate large-scale alien plant control operations (van Wilgen and Wannenburgh 2016). At the time, it was estimated that more water could be delivered, at a lower unit cost, by integrating alien plant control with the maintenance of water supply infrastructure, than without control . ...
South Africa has much to offer as a location for the study of biological invasions. It is an ecologically diverse country comprised of nine distinct terrestrial biomes, four recognised marine ecoregions, and two sub-Antarctic Islands. The country has a rich and chequered socio-political history, and a similarly varied history of species introductions. There has been a long tradition of large-scale conservation in the country, and efforts to manage and regulate invasions began in the nineteenth century, with some notable successes, but many setbacks. With the advent of democracy in the early 1990s, South Africa established large alien species control programmes to meet the dual demands of poverty alleviation and conservation, and has since pioneered regulatory approaches to address invasions. In terms of research, South Africa has played an important role in the development of invasion science globally. It continues to have one of the most active communities anywhere in the world, with strengths in theoretical and applied invasion science, and world-leading expertise in specific sub-disciplines (e.g. the classical biological control of invasive plants).
... Currently, there is intense concern over water resource degradation and the unequal distribution of water resources has become a topic of interest for the research community (Alperovits and Shamir, 1977;Morgan and Goulter, 1985;Cunha and Sousa, 1999). Intense progress on water resources has been observed over the past years including a variety of topics such as water resources monitoring (Resh et al., 1995;Sawaya et al., 2003), water treatment technology (Gahr et al., 1994;Dossantos and Livingston, 1995;Oturan, 2000;Bhojwani et al., 2019) and management of water resources (Andreu et al., 1996;Le Maitre et al., 1996;Middelkoop et al., 2001;Al-Jawad et al., 2019). ...
A bibliometric analysis of research articles published on water-use efficiency was performed using the Web of Science database and evaluated. Journal titles, publication years, subject categories, keywords and countries publishing were obtained. A number of 2077 papers were retrieved, two-thirds of them published in the last decade. The articles were published in 439 journals, with Agricultural Water Management , Agronomy Journal, Crop Science, Field Crops Research and Indian Journal of Agricultural Sciences the most productive. Most of the leading productive journals have Impact Factors in the top quartiles of the Journal Citation Reports. Agronomy, Plant Sciences, Water Resources and Agriculture Multidisciplinary were the most common journal subject categories, indicating a wide diversity of research fields ascribed to this topic. The predominant key words and phrases used were growth, ‘carbon isotope discrimination’, yield, photosynthesis, ‘gas exchange’, evapotranspiration and ‘stomatal conductance’. The productivity ranking for countries was headed by China (456 papers), followed by the USA (410), Australia (176) and India (165). A content analysis of the papers made identification of the key issues of greatest scientific concern possible, as well as their evolution over time. The most cited papers relate to physiological aspects, but also important studies on experimental biology, drought resistance, effects of climate, crop production and ecology, among others.
... AGALDO However, problems associated with invasive plant species in most of Africa remain unclear due to limited understanding of the stages of invasion as well as the impact on native species (Witt, Beale, & Wilgen, 2018). This is because little has been done to understand plant invasions in most of Africa, although a few studies in Uganda (Shackleton, Witt, Aool, & Pratt, 2017;Totland, Nyeko, Bjerknes, Hegland, & Nielsen, 2005) and South Africa have been carried out to study the impact of Lantana camara L. (Lamiales: Verbenaceae; hereafter referred to as L. camara) on different ecosystems (Le Maitre, Wilgen, Chapman, & McKelly, 1996;Nel et al., 2004;Richardson & Van Wilgen, 2004;van Wilgen, Reyers, Maitre, Richardson, & Schonegevel, 2008). ...
Lantana camara (Lantana) is an invasive species of South American origin, and it is visibly widespread in Amurum Forest Reserve (AFR) Jos‐Plateau, central Nigeria. Presently, there is no baseline study on Lantana and its spread despite its conspicuous presence within AFR. This is the first study to investigate its abundance and interactions with native fauna and flora in AFR. Established study plots were used to estimate its relative abundance in three habitat types (gallery forest, savannah woodland and rocky outcrops) and to investigate its effect on plants. An experiment using cowpea‐tested allelopathic effects of Lantana and focal observation/beating tray method was used to collect data on vertebrate and invertebrate species utilising/interacting with Lantana. Lantana is widespread within AFR occupying 77% of plots with the gallery forest habitat having the highest abundance compared with the savannah woodland and rocky outcrop. Plots with Lantana had fewer woody plant species than plots without Lantana. Tests on soil samples from the reserve for basic properties revealed that Lantana‐infested sites had relatively poor soils compared with non‐Lantana‐infested sites. Birds and insects in AFR utilise Lantana and are probably responsible for its spread. Control measures are necessary to limit its spread and mitigate its likely negative effect on plant species.
... These effects may be caused directly by allelopathy and competition for resources (Maron & Marler, 2008) or indirectly by modifying the environment to the detriment of native species in their own benefit (Niu, Liu, Wan, & Liu, 2007). In particular, the effects that IAPs can have on the environment range from changing fire and hydrological regimes (Le Maitre, Van Wilgen, Chapman, & McKelly, 1996) to the alteration of carbon and nitrogen cycle (Ehrenfeld, 2003) by affecting several processes including nitrogen fixation, soil nitrogen mineralization (Hawkes, Wren, Herman, & Firestone, 2005), plant nutrient uptake, and nutrient transfer to soil through litterfall (Lindsay & French, 2005). ...
Invasive alien plant species (IAPs) represent one of the main biological threats to biodiversity worldwide. Information about their phenotypic plasticity are needed to increase awareness about their future invasive potential. A study about phenotypic plasticity in response to contrasting light regimes and its quantification by a plasticity index (PI) of two IAPs (Ailanthus altissima and Robinia pseudoacacia) inside a Strict Nature Reserve was conducted. R. pseudoacacia showed a 70% higher PI, with a strongly greater value at morphological leaf level, associated with a greater ability to survive and grow in forest understory, explaining its greater widespread. Otherwise, A. altissima showed its highest PI at physiological level, which was associated with the ability to colonize and grow in environments with high-light regimes. Based on these results, the conservative management has limited the presence of A. altissima by its lower ability to grow in forest understory. In fact, the small-scale gaps in the forest infrastructure, that could allow its recruitment, are originated only from the death of a single tree or small group of trees. Regarding R. pseudoacacia, it is critical to maintain this type of management because any disturbances resulting in large openings could further promote its presence inside the Reserve.
... Alien plant invasions have significant negative effects on grassland processes and patterns, as well as water purification and retention. Alien plants are well-known to use more water and lose it through transpiration than indigenous species (Le Maitre et al., 1996). Fragmentation of the grassland environment has negative effects on the grassland processes and patterns while also possibly having a negative effect on climate change. ...
Livestock production is critical to rural livelihoods across Southern Africa, providing socio-economic and nutritional benefits. Consequently, seasonal and long-term limitations to ruminant production can directly impact food security, nutrition, and livelihoods at individual, local and regional levels. Despite progress in livestock science research in recent years, the seasonal availability and quality of feed remains one of the key challenges to livestock productivity in Southern Africa. In particular, dry weather conditions, the lack of rain and lower temperatures in the dry season cause herbaceous plants to die back and browse species to defoliate, limiting the abundance, quality, and variety of feed available. This creates a ‘Nutritional Feed Gap’, defined as the combined effect of the sharp reduction in both forage quantity and quality from the wet to the dry season and the risk that poses to ruminant production systems. Understanding the nature and extent of how seasonality impacts ruminant production potential can thus contribute towards mitigating such issues. In this review, we characterise this nutritional feed gap in terms of forage abundance and nutrition as well as discussing how climate change may shape the future nutritional landscape and key areas for future research.
Invasive plants affect the capacity of ecosystems to perform key functions, including primary production, nutrient and water cycling, decomposition, energy flow through food webs, or control of disturbance regimes, hydrology, and sedimentation. Invasive plants can also change the composition and structure of the resident community through different mechanisms, including direct competition, allelopathy, habitat alterations, and hybridization. Both changes in ecosystem functionality and community structure affect the capacity of ecosystems to deliver the three categories of services that contribute to human well-being: provisioning (e.g., food, water, wood, medicines, etc.), regulating and maintenance (e.g., climate regulation, erosion control, flood regulation, fire protection, regulation of soil fertility and water quality, etc.), and cultural (e.g., spiritual, intellectual, or symbolic assets). Invasive plants can also increase the negative effects of ecosystems on human well-being (i.e., ecosystem disservices, such as allergies and infrastructure damage). Impacts on ecosystem services may vary in magnitude and direction depending on the type of invader, the invasion scenario, and the spatio-temporal scale. Also, synergies and trade-offs between ecosystem services may arise when invasive species promote many services simultaneously or favor some services at the expense of impairing others. For example, some invasive plants can act as C sinks, increase timber provision, and contribute to the formation and protection of soil against erosion, while simultaneously increasing fire risk through increased fuel input, declining water provision through high water consumption, or reducing landscape aesthetics. Climate change may create opportunities for some invasive species and alter the severity of their impacts on ecosystem services, through alterations in species distributions, biological interactions, and ecosystem processes. Indeed, the synergistic effect of invasive species and climate change often cause the most detrimental outcomes for ecosystems.
In this chapter, we first compile information regarding the impacts of plant invasions on ecosystem functionality, focusing on key functions that regulate the fluxes of energy and cycles of matter. Then, we examine how those changes affect the delivery of provisioning, regulating, and cultural ecosystem services. Lastly, we analyze the role of climate change in altering the impacts of invasive plants on ecosystem functionality and ecosystem service delivery. We recommend that future studies investigate how climate change affects the impact of invasive plants on multiple ecosystem processes and services, rather than considering them in isolation. This would improve decision-making on invasive species management under climate change.
Land management is necessary to maintain valuable landscapes in which biodiversity conservation and sustainable human use of resources coexist. The management at large scale (e.g., at watershed scale) focusing on keystone species assures the conservation of important processes like population and community dynamics, and resources conservation.
Human life and other biotic organisms inhabiting Earth are endangered due to the vagaries of climate change, overexploitation and unsustainable use of natural resources like freshwater ecosystems, forests, genetic resources, wildlife and land use, etc. While emphasizing on the vitality of natural ecosystems and the goods and services accruing from them for human and other biotic organisms, focus is also reinforced on the conservation and sustainable use of natural resources to ward off adverse impacts of climate change and sustain the continuity of life cycle on Earth.
The Keiskamma catchment has undergone significant land use/cover changes (LUCC) and invasion by Pteronia incana (P. incana) shrub, and the hydrological implications of the phenomena are not fully understood. This study assessed the hydrological response of the catchment using remote sensing per-pixel classification, the SWAT model between 1994 and 2016, and field experiments. Results revealed a significant increase in woody vegetation encroachment and a decrease in mean annual streamflow, runoff, soil water content, evapotranspiration and groundwater. However, high surface runoff, and sediment loss were evident under P. incana invader shrub at hillslope scale. The study concludes that the hydrological response of the catchment was influenced significantly by LUCC in the form of extensive invader shrub encroachment, expansion of exotic forest tree species, impoundments and infestation of riparian zones by invasive vegetation. Control of alien invasive plants and utilization of indigenous forest species are recommended for catchment management.
This chapter reviews the increasing importance of Mediterranean pines as invasive non-native species outside the natural range of the genus, especially in temperate parts of the Southern Hemisphere where several species are important weeds. It first discusses human-mediated changes to the ranges of Mediterranean pines and their colonization and persistence ability within and immediately adjoining their natural ranges. Next, it reviews the history of plantings and emergence of invasions of these pines in the Southern Hemisphere. Aspects of the ecology of the most widespread invaders (P. halepensis and P. pinaster) are discussed by considering the factors that influence invasive success. The impacts of the invasive pines are discussed, and management approaches and challenges are reviewed.
Giant reed (Arundo donax L.), a woody grass native to the Mediterranean, has become a cause of concern for national water security in its invaded range of the arid southwestern United States, Australia, New Zealand, and South Africa. The main objective of this study was to provide the first, landscape-level estimates of water use by giant reed. The study utilized the eddy covariance method to quantify evapotranspiration (ET) throughout the 2014 and 2015 growing seasons along the Rio Grande River in Eagle Pass, Texas. We monitored ET concurrently with the implementation of a biological control program targeting giant reed. Daily ET rates were strongly associated with the phenology of giant reed, as estimated by degree day accumulation. Monthly ET was higher in each month of the active growing season (May–October) of giant reed in 2014 than in 2015. Consequently, seasonal (DOY 121-304) ET was substantially higher in 2014 (842 mm) than in 2015 (625 mm) even though the 2015 growing season was wetter. Cumulative rainfall from May to October was 188 and 264 mm in 2014 and 2015, respectively. Our study indicated that the reduction in ET could be attributed to the presence of specialist insect biological control agent, the stem-galling arundo wasp (Tetramesa romana). In 2015, we observed a 28.6% (May), 53.5% (June), and 44% (July) increase in the number of arundo wasps captured in sticky traps from the previous year. Additional studies are needed to quantify conservation and economic benefits of the biological control program in the Rio Grande Basin.
Since 1995, the South African government has spearheaded a national invasive species campaign known as the Working for Water Program with the dual objectives of invasive species eradication and rural development. This national narrative on invasive species reflects a politicized research agenda and a wealth of material resources directed toward eradication, yet does not accurately portray the reality of invasion at the village level. In particular, Acacia mearnsii de Wild, or the black wattle tree, is classified as one of the worst invasive species in South Africa and a primary target for Working for Water, yet represents an important livelihood resource for rural communities and impacts community members differentially. To better understand these local rural realties, I use a critical invasion science approach to interrogate the local experiences and narratives of black wattle invasion in a rural pastoral community in the Eastern Cape. Within this community, local understandings and impacts of black wattle are nuanced, spatially variable, and reflect complex knowledge politics and political economies. As invasion research moves to incorporate the human and local dimension of invasion for improved policy, it is imperative to fully consider this differentiation of perspectives and impacts within the local community.
Native riparian plant communities are profoundly threatened by invasions of alien plants in Japan. At present, the proportion of vegetation area dominated by alien plants accounted for about 15 percent in the rivers administrated by the Ministry of Land Infrastructure and Transport. Displacement of native plant communities by invasive alien plant species is altering riparian ecosystems substantially. To preserve riparian plant communities , active management to suppress the dominance of invasive alien plants is urgently required. Weed control methods in agricultural ecosystems, which usually have strong side effects on various organisms and tend to simplify the ecosystem, are not suitable for the control measures for biodiversity conservation. Ecosystem approaches, focusing both management of invasive species and restoration of sound ecosystems simultaneously are desirable. Ecosystem management on the invasive species populations and habitat restoration should be based on sufficient information on the population ecology, and the causal factors enhancing ecosystem invasibility.
This chapter provides an overview of the researchers and research initiatives relevant to invasion science in South Africa over the past 130 years, profiling some of the more recent personalities, particularly those who are today regarded as international leaders in the field. A number of key points arise from this review. Since 1913, South Africa has been one of a few countries that have investigated and implemented alien plant biological control on a large scale, and is regarded as a leader in this field. South Africa was also prominent in the conceptualisation and execution of the international SCOPE project on the ecology of biological invasions in the 1980s, during which South African scientists established themselves as valuable contributors to the field. The development of invasion science benefitted from a deliberate strategy to promote multi-organisational, interdisciplinary research in the 1980s. Since 1995, the Working for Water programme
has provided funding for research and a host of practical questions that required research solutions. Finally, the establishment of a national centre of excellence with a focus on biological invasions has made a considerable contribution to building human capacity in the field, resulting in advances in all aspects of invasion science—primarily in terms of biology and ecology, but also in history, sociology, economics and management. South Africa has punched well above its weight in developing the field of invasion science, possibly because of the remarkable biodiversity that provided a rich template on which to carry out research, and a small, well-connected research community that was encouraged to operate in a collaborative manner.
Considerable advances have been made since the first estimates of the impacts of invasive alien plants on water resources in the early 1990s. A large body of evidence shows that invasive alien plants can increase transpiration and evaporation losses and thus reduce river flows and mean annual runoff. Riparian invasions, and those in areas where groundwater is accessible, have 1.2–2 times the impact of invasions in dryland areas. The magnitude of the impacts is directly related to differences between the invading species and the dominant native species in size, rooting depth and leaf phenology. Information on the impacts has been successfully used to compare the water use of invasive plants and different land cover classes, to quantify the water resource benefits of control measures, and to prioritise areas for control operations. Nationally, the impacts of invasive alien plants on surface water runoff are estimated at 1.44–2.44 billion m³ per year. The most affected primary catchments (>5% reduction in mean annual runoff) are located in the Western and Eastern Cape, and KwaZulu-Natal. If no remedial action is taken, reductions in surface water runoff could increase to 2.59–3.15 billion m³ per year, about 50% higher than current reductions. This review illustrates the importance of measuring water-use over as wide a range of species as possible, and combining this with information from remote sensing to extrapolate the results to landscapes and catchments. These methods will soon provide much more robust estimates of water use by alien plants at appropriate spatial and temporal scales. The results of these studies can be used in water supply system studies to estimate the impacts on the assured yields. This information can also be used by catchment water resource managers to guide decision-makers when prioritising areas for clearing and rehabilitation, and for targeting species for control measures.
The present study attempted to bridge some gaps in the existing literature evaluating the net economic worth of South Africa’s Working for Water (WfW) programme for eradicating invasive alien plant species (IAPS). Specifically, the study employed the social benefit-cost analysis (BCA) methodology to assess the impact of accounting for the opportunity cost of invested capital funds and treating labour as a social benefit on the social worthiness of the WfW programme in the Inkomati catchment. The study also used improved measures of the value of other ecosystem services, particularly the carbon sequestration values. Results of the social BCA provided strong empirical evidence in support of the continuation of IAPS eradication activities, as economically and socially worthwhile investment of the country’s resources. The programme generates higher net worth under lower rates of discounting future values. This confirms the importance of the water-saving benefits, which continue theoretically for ever, at zero cost to the society, as all direct and indirect financial costs cease upon completion of the eradication operations. The social net worth of the IAPS eradication programme obviously increases when expenditure on labour wages was considered a social benefit rather than a direct financial cost, even under strict project funding scenarios that require funding through private capital markets, i.e., paying commercial rates of interest. However, more strategic planning for the control of IAPS is critically important given their high cost. Challenges facing the sustainability of IAPS eradication programmes in the study area and South Africa include: raising sufficient funding from private and public sources, and introducing incentive systems to encourage higher collaboration and participation of private landowners in the currently primarily publicly driven IAPS eradication efforts. The study also suggests a number of policy and technological reforms to address the said challenges.
Arid and semi-arid regions of central India receive scarce and episodic precipitation during the short monsoon season, and also experience substantial evaporation. Traditional and innovative water harvesting and governance practices improve water stewardship, or abate some impacts of intensive mechanised water extraction. However, significant numbers of alien trees, in particular Eucalyptus species with high water demands, populate some regions practicing progressive water stewardship. The water demands of these trees can potentially undermine efforts to achieve water security. Through interviews with community leaders in Indian villages with differing eucalyptus tree densities, water loss through evapotranspiration compared with livelihood demands was approximated. Literature review of the water demands and ecosystem services provided respectively by alien eucalypts and native, culturally valued neem trees supports assessment of the likely benefits and acceptability of a replacement programme favouring native trees. Although data limitations mean that the findings of this study are necessarily uncertain, they nonetheless illustrate the likely scale of impact, substantiating the case for alien tree management as an important contribution to water security. Alien vegetation management practices as a contribution to water security are already firmly established in South Africa, and are likely to yield equivalent benefits if translated to dryland India.
Tree invasions into native grasslands and shrublands are global phenomena, with alien tree invasions occurring on nearly every continent. We hypothesized that wood nutrient concentrations are a key trait to enable successful tree invasions in regions limited by soil nutrient availability, such as the fynbos vegetation of the Cape Floristic Region of South Africa. We sampled wood and bark of a height range of indigenous and alien woody species within the Cape Floristic Region. We used linear regression and phylogenetic analyses to assess associations between wood nutrients and tree height and analysis of variance to assess how wood nutrients vary across vegetation types. Alien trees had lower wood nutrient concentrations than many native trees, and nutrient concentrations, especially not only N and P, but also Mg and K, were negatively associated with tree height. These results suggest that recent tree invasions into the nutrient‐poor fynbos shrublands may be a result of low wood nutrient concentrations that allow the alien trees to successfully overtop the native vegetation. This indicates that wood nutrient concentrations may be a useful trait to predict whether an alien tree species has a greater potential of becoming invasive in regions with limited soil nutrients.
Pinus halepensis, introduced into South Africa from the Mediterranean basin in the mid-nineteenth century, has become an important weed in the fire-prone mountain fynbos of the Cape Province. The age structure in a self-sown stand of P. halepensis at Miller’s Point near Simonstown was determined in 1986 from counts of growth rings. The oldest tree at the site was 58years old but only two of the 657 trees that made up the 1986 stand were present before the last fire in 1972. Nearly 50% of the surviving trees established within 1year of the last fire and less than 1 % of the surviving trees established more than 4years after the last fire. Seedling regeneration after a fire in part of the stand in March 1986 was prolific and an average of 465 seedlings were counted on six 50-m² plots 8months after the fire. The survival and proliferation of P. halepensis is ascribed to the early attainment of reproductive maturity and the ability of seeds to germinate and establish in the immediate post-fire environment.
Aerial plant biomass has been sampled by harvesting on several sites in fynbos communities of the southwestern Cape Province. Biomass in stands of about two years old ranged from about 2 200 kg per ha to about 7 500 kg per ha. Mature stands comprised about 11 000 to 15 000 kg per ha in heaths and 15 000 to 26 000 kg per ha in sclerophyllous scrub. The data indicate a maximum annual growth rate of 1 000 to 4 000 kg per ha early in the development of a stand, but growth rates appear to decline rapidly as communities age. Young stands are dominated by hemicryptophytes, which comprise about 2 000 to 6 000 kg per ha, or about 60 to 75 per cent of the biomass in stands of about four years old. Shrubs become prominent later, but the hemicryptophytes persist. The data indicate that the biomass, growth rates and the shape of the growth curves of fynbos communities are on the whole similar to those of analogous vegetation in other zones of mediterranean type climate. However, there are important structural differences in that analogues of the northern hemisphere (garrigue, chaparral) do not have a significant component of persistent hemicrytophytes. Although Australian heath communities do have this feature, the hemicryptophytes are not as prominent as in fynbos.
Fuel mass in fynbos was less than half that in the forest. The forest was taller and had a pronounced separation between the litter layer and tree canopies. The ratio of fuel volume to fuel-bed volume of forest species was half that of fynbos species, reflecting the sparse nature of the crowns. Foliar moisture contents of forest trees were 50-100% higher than in fynbos plants. Heat yields were marginally higher (21 860 J g-1) in fynbos than in forest species (20 703 J g-1). Crude fat contents of forest species averaged c3% of dry mass. Fat contents were more variable among the fynbos species, but some species had high (6-10%) fat contents. A modified Rothermel fire model predicted flame lengths of 0.7-4.9 m in fynbos under low to extreme fire hazard conditions, but predicted that fires would fail to burn in forest vegetation under the same conditions. The physical and chemical make-up of fynbos favours fir. It is more flammable than Chilean mattorral, but is less flammable than Californian chaparral or Australian Eucalyptus woodlands due to lower crude fat contents and higher foliar moisture contents. Although narrow forest strips may be scorched by intense fires in adjacent fynbos, it seems unlikely that extensive forest patches would burn under the conditions usually selected for prescribed burning operations. -from Authors
Mean aboveground live biomass was 510 g m⁻². The Braun-Blanquet table method was used to define 10 vegetation communities. Descriptions of plant communities ranging from low herblands to woodlands are presented. Soil moisture and drainage appear to govern community distribution. Descriptions of selected soil profiles in each community are presented. Additional physical factors such as fire and wind may be important in determining vegetation structure. Large seed-reproducing shrubs are rare. - from Authors
Data on the seed morphology of three pine species (Pinus pinea L., P. pinaster Ait., and P. radiata D. Don) in the south-western Cape Province are presented. The seeds of both P. pinaster and P. radiata are relatively small (50 and 20mg respectively) and have relatively large wings (190 and 110mm² respectively). Pinus pinea, on the other hand, has a relatively large (700mg) seed and a small wing (24mm²). We show that P. pinaster is capable of dispersal away from the parent trees, whereas P. pinea seedlings occur only under parent trees. This supports the hypothesis that P. radiata and P. pinaster tend to be invasive by virtue of possessing winged seeds adapted for long-range dispersal.
Streamflow records from three subcatchments in the Zachariashoek research area near Paarl in the south-western Cape were analyzed to determine the effects of prescribed burning of fynbos vegetation on streamflow. Results indicate that burning six-year-old vegetation increased streamflow significantly. The most marked changes occurred in the 12-month periods immediately following two consecutive fires (1971 and 1977) in the same catchment. Streamflow increased by an average of 7. 1 mm/month (15% of the average monthly discharge over the three calibration years) after the 1971 burn, and by an average of 5. 7 mm/month (7% of average monthly discharge over six calibration years) following the 1977 burn. Burning of twelve-year-old vegetation in another catchment did not cause any significant increase in streamflow.
Acacia cyclops is found along the coast of SW Australia and of mediterranean-climate South Australia, associated with naturally- and artificially-disturbed habitats. Reproduction occurred only by seed. Birds have distributed the seed in regurgitated pellets or in faeces. Pellets were usually associated with feeding sites while faeces were common under perches and near watering points. Seed moved in these ways was found <200 m from the nearest mature bush. Secondary dispersal of seeds by 6 ants species was observed. Ants left seeds on the surface or took them into their nests: dispersal distances were <2 m. Seed-feeding bugs were common in the litter beneath bushes but absent from bare ground. Higher temperatures experienced by seeds on bare ground are likely to enhance germination. Dispersal away from canopies onto bare ground may allow successful establishment because of reduced predation and enhanced changes of germination and establishment.-from Author
Pinus radiata, an important plantation species in South Africa, also invades mountain fynbos in the S and SW Cape Province and is a threat to the conservation of this vegetation type. Invasion began almost immediately after the first release of seeds from an adjacent plantation. Initial colonizers established at distances of up to 3 km from the seed source. Populations increased rapidly after a fire and resultant stands were dominated by cohorts that established during the immediate post-fire phase. Where fire had been excluded, population growth was slower and less dense, uneven-aged stands resulted. -from Authors
(1) The South African vegetation type fynbos (macchia) is fire-adapted and fire-dependent. (2) Four sites which differed in the frequency with which they had been burned were sampled towards the end (4-37 yr) of a period between fires. (3) The above-ground shoot biomass was determined from clipped plots and regression analysis. Shoots smaller than 6 mm diameter were considered to be potential fuel. (4) The biomass was 670 g m-2 4 yr after burning; all of this was potential fuel. Fynbos 21 yr after burning had a biomass of 5100 g m-2 of which about half was potential fuel. Fynbos protected from fire for 37 yr had a biomass of 7600 g m-2, of which more than half was potential fuel. (5) Frequent burning keeps the biomass low. Protection from fire for longer than 30 yr results in a decline in live biomass and an accumulation of litter and potentially burnable vegetation. Fires in such senescent stands are usually very severe.
(1) South African fynbos vegetation is fire-prone and susceptible to invasion by alien shrubs. Alien shrubs change the nature of the fuel bed and thus affect fire behaviour. (2) Changes in biomass, size and distribution of plant parts as fuel and plant moisture and energy contents were determined at two sites invaded by the important alien shrubs Hakea sericea Schrad. and Acacia saligna (Labill.) Wendl. (3) The data were used to define fuel models and to simulate fire behaviour using Rothermel's fire model. This simulation was used to test the hypothesis that invasion increases fire hazard through increasing fuel loads. (4) Invasion by H. sericea resulted in a 60% increase in fuel load and lowered the moisture content of live foliage from 155 to 110%. Simulated rates of fire spread and intensity were nonetheless lower than in fynbos due to a densely-packed fuel bed. (5) Invasion by A. saligna resulted in a 50% increase in fuel load. The high moisture content of foliage of this shrub (about 270%) effectively reduces the fuel load and fuel bed depth, resulting in low rates of fire spread and intensity in the simulation. (6) Shortcomings in Rothermel's model prevented the accurate simulation of high intensity fires which have occurred in invaded areas under extreme weather conditions. Such fires vigorously consume the increased biomass of shrub crowns, are difficult to content of foliage of this shrub (about 270%) effectively reduces the fuel load and fuel bed Under such conditions, the fire hazard will be increased by invasion.
A sampling trial for the estimation of the above biomass was undertaken in the Bosboukloof catchment at Jonkershoek State Forest. Eighty-five trees were felled, after which the oven-dry weight of stem-wood, bark, branches and foliage was estimated by subsampling. The weight of stemwood and bark of each sample tree was obtained from a subsample within each tree, that of branchwood and foliage by the application of regression analysis to combined subsamples of branches.
Grazing compared with mowing had no significant effect on population growth, dispersal or area occupied for any species. C. tenuiflorus populations had greater dispersing fractions than the other species, and this appeared to be influenced by wind. This species also had a greater initial population growth and spread. In the 2nd year, the population of C. tenuiflorus declined in grazed and ungrazed treatments, attributed to its population's tendency to establish each year from a single cohort. Although the population size and dispersal gradients of A. fatua and O. acanthium were similar after 2 yr spread for each species, O. acanthium occupied a greater area owing to a higher frequency of low density patches. Spread rades for O. acanthium, A. fatua and C. tenuiflorus respectively, increased, remained constant and decreased with time. -from Author
The reduction of species richness of indigenous plants is one of the major problems associated with the presence of dense stands of invasive alien trees and shrubs in the Fynbos Biome of the Cape Province, South Africa. A synthesis was made of published and unpublished data on plant species richness in fynbos with different levels of invasion and different histories of control. Linear regressions of species richness on the log of quadrat size were significant for both uninvaded fynbos and fynbos under dense stands of alien trees and shrubs. The slopes of the regression equations did not differ significantly between invaded and uninvaded sites, but elevations were significantly different, indicating a marked reduction in richness of indigenous plant species in invaded areas. The linear regression of species richness on quadrat size for cleared areas was not significant, but quadrats at most cleared sites showed species richness values intermediate to those of uninvaded fynbos and dense stands of aliens. Reductions in species richness at the scale of the sample quadrats used in this study (4–256 m) occur once the canopy cover of aliens exceeds about 50% and there is evidence of reduced species richness with increased time of suppression. For this reason, stands should be cleared before canopy closure is achieved.
This paper deals with a preliminary study of the aboveground biomass of Pinus radiata in the Jonkershoek State Forest. A sample of 25 twenty-nine year old trees was selected from comp. 35A. The oven-dry stem mass was estimated by subsampling each stem and regressing the estimated oven-dry mass on DBH (r = 0,9767). Similarly, a sample of branches, representing the range of branch diameters, was drawn, their oven-dry mass was determined and subsequently regressed on branch diameter (r = 0,9751). Branch mass per tree was estimated by sampling the distribution of branch diameters for each tree separately. A reliable estimate of crown mass (r = 0,8385) and total aerial mass (r = 0,9776) from DBH is also made. Total estimated above-ground biomass for the stand amounted to 184860 kg ha-1 , of which 89 per cent was stem wood and the remainder crown.
The relative sizes and composition of soil seed banks, the influence of fire and the post‐fire deposition of seeds were investigated in a riparian forest and adjacent fynbos and transitional vegetation in Swartboskloof. Brief complementary studies of soil seed banks were conducted in poorly‐developed forest and scree forest soils. Numbers of species in each vegetation type were very similar, but there were fewer seeds in riparian forest soil than in the transitional and fynbos zones. These patterns were not repeated in poorly‐developed forest and scree forest. No effects of fire on soil seed banks were detected. Forest soil had relatively large numbers of seeds stored at 10 to 15 cm deep, with many zoochorous and few myr‐mecochorous seeds.
Anemochorous and ornithochorous seeds of forest species formed a major component of seed deposition within the transitional and fynbos zones in the first year after fire. The numbers of anemochorous forest seeds in the fynbos declined with distance from the forest edge. The deposition of ornithochorous forest seeds was less closely related to distance from the source, and was not exclusively associated with the presence of tall or fruit‐bearing shrubs.
Regeneration after canopy‐destroying disturbance in the forest is likely to emanate from the soil seed banks of pioneer species which now or previously occurred on forest margins. Seed availability does not appear to limit colonization of fynbos by forest species soon after fire.
In South Africa seedlings of the exotic Acacia cyclops grow in clumps. The seedlings occur beneath tall elements, or in bush clumps, of the surrounding indigenous vegetation. The tall shrubs are used as perches by birds, and the pattern of seedling distribution is a result of dispersal of seeds by birds. Germination of A. cyclops seeds was enhanced as a result of passage through the gut of a bird, or by artificial treatments simulating actions taking place in the gut of a bird. We examine properties of the seed, and the funicle which is attractive to birds, in relation to aspects of the life history of A. cyclops and the species' success as an invasive plant in South Africa.
A model is developed to define the efficacy of dispersal in relation to safe site area and seed production. Efficacy is measured as the expected number of progeny from one parent. It is shown that maximization of efficacy does not depend on the density of safe sites. When safe sites are confined to a restricted area around the parent, and safe sites are small or few propagules are produced, dispersal curves with short tails are most efficacious; when safe sites are larger or when more propagules are produced, distributions with longer tails become more advantageous.
For plant species, the most immediate function of dispersal is the placement of propagules in safe sites where they can grow and survive. The efficacy of any mode of dispersal is measured by the number of propagules so placed, and depends on the distribution of distances traveled by propagules and by the density of safe sites. A graphical model is developed to describe the relationship between these two factors, and to provide a method for comparing the efficacy of dispersal in different species. When safe sites are rare, distributions of distances with long tails are most efficacious; when safe sites are more abundant, distributions with broader peaks are more suitable. This analysis is shown to apply in a qualitative fashion to a group of species inhabiting the eastern forests of North America.
Four shrub species of the Australian Proteaceae (Hakea sericea, H. gibbosa, H. suaveolens and H. salicifolia) were introduced to South African fynbos shrublands between 1840 and 1860. H. sericea is highly invasive, H. gibbosa and H. suaveolens are moderately invasive and H. salicifolia is not invasive. The allocation of reproductive energy, germinability, the ability to survive fires and to germinate in burnt and unburnt areas, and the nutrient content of seeds were assessed for the four species. The information was used to investigate whether the success of H. sericea relative to the other three species could be explained by the superior expression of any trait. The most important trait which separates H. sericea from the other species is its ability to produce a large seed bank in its adopted environment in the absence of seed predators. Seed production in H. sericea shrubs with an above-ground dry mass of 8 kg is four times greater than H. gibbosa and more than 16 times that of H. suaveolens. Although H. salicifolia also produces a large seed bank, its seeds are unable to survive fires due to inadequate insulation by the small follicles. The results are compared to dispersal and seed bank data for indigenous South African Proteaceae, which have low dispersal and suffer high pre-dispersal seed predation. We suggest that potential invasives in the fynbos can be identified as species that have: (i) a potentially high seed production that is limited by specialized predators; (ii) an ability to disperse over long distances; and (iii) are pre-adapted to frequent fires and low soil nutrients. The data also support the current strategy of combatting H. sericea using specialized insect seed predators.
The development of a model of plant spread, INVADE, is described. It is a FORTRAN 77 program that will run on any IBM-compatible computer. Output is in the form of a matrix of 23 × 23 cells or a limited output version which is only total population for the matrix. The model was used to simulate spreading populations of Avena fatua over 3 years and its output compared with populations arising from deliberate introductions in the field. The population growth rate of A. fatua was markedly affected by the contrasting rainfall which occurred during the tests and the estimate of growth rate at a focus (or cell) based on Year 1 data for subsequent years was a large overestimate. However, with a given population growth rate per cell for each year, the model accurately predicted total population, area occupied and gross distribution of A. fatua. Possible uses of the model are described.
A wildfire in February 1986 destroyed most of an afforested research catchment in the southwestern Cape region of South Africa. The hydrological consequences of the fire were quantified using monitored pre-fire and post-fire stream flow and sediment data from the burned catchment and a nearby control catchment. Soil loss and soil wettability were also measured.In the first year after the fire, weekly stream flow totals increased by 12%, quick flow volumes increased by 201%, peak flow rates increased by 290% and catchment response ratio increased by 242%. Soil loss on overland flow plots ranged from 10 to 26 t ha−1, and suspended sediment and bedload yields each increased roughly four-fold following the fire.Wettability of the soils was greatly reduced by the passage of fire. Surface soil layers (0–10 mm) were burned clean of any inherent water repellency by the passage of a hot fire, but more severe repellency, in broader bands, was induced in deeper soil levels by the heating of the soil. It is postulated that the widespread development of water repellency in the soil led to overland flow during larger rainstorms, which in turn caused the markedly altered hydrological behaviour of the catchment and the high soil losses relative to the unburned condition.
Thesis (M.Sc.) (Botany)--University of Cape Town, 1972.
In this report a list is given of 1 808 rare, threatened and recently extinct plants in the fynbos and karoo biomes in the Cape Province of South Africa. The area covers the south-western and southern Cape, Namaqualand and the Karoo. Following the IUCN categories the area has 29 plants Extinct, 118 Endangered, 183 Vulnerable, 495 Critically Rare. 281 Indeterminate and 702 Uncertain. Local lists are given for the main biogeographic zones in the area. The extent and causes of the threatened plant problem are discussed and lines along which research and conservation action might follow are proposed. Data are provided on the populations and conservation priorities of about 250 species
A scheme of major categories of the vegetation in and adjacent to the fynbos biome is given as a second approximation after Acocks1 Veld Types (1953). A four tier hierarchy is presented with nineteen categories of vegetation. The major subdivisions recognized on the basis of their structural, environmental and floristic characteristics are: Cape Fynbos Shrublands; a mosaic of Cape Fynbos Shrublands and Subtropical elements; Cape Transitional Small-Leafed Shrublands; Cape Transitional Large-Leafed Shrublands; Subtropical Transitional Thicket; Afromontane Forest; and Karroid Shrublands. In addition a vegetation map on which these categories were recognized was produced independently using Landsat imagery.
Copyright: 1993 Academic Press Limited Managers of natural areas require a wide variety of up-to-date and accurate information and maps to manage their lands effectively. This paper reviews the objectives of conservation management, and the problems faced by mountain catchment managers, in the Cape Province, South Africa. The manager’s information requirements, system design concepts and the first phase of the development of computerised database are described. The system has two concepts: a spatial database developed using geographic information system (GIS) software on a workstation, and a desktop computer database (PC system) developed using a standard relational database package. The GIS is used to generate the links that the PC system uses to associate spatial entities such as land ownership boundaries, land management units (compartments) and vegetation types. It also used to calculate spatial statistics such as the area of a compartment or vegetation type or the length of a road or path, A variety of maps are produced, including an opaque base map and clear overlay maps showing features such as compartment and fire boundaries, post-fire vegetation age and the distribution and density of alien weeds. It also has routines to calculate fire hazard based on post-fire age and fuel accumulation models for the different vegetation types occurring in the catchment areas. The PC system gives the manager access to his data and provides a scheduling routine for assigning priorities for planned fires. Future developments will include an expert system for planning control operations for alien plant species.
Impacts of woody aliens on ecosystem properties. The Ecology and Control of Biological Invasions in South Africa
- D B Versfeld
- B W Van Wilgen
Versfeld, D.B. & van Wilgen, B.W. (1986) Impacts of woody
aliens on ecosystem properties. The Ecology and Control
of Biological Invasions in South Africa (eds I.A.W. Macdonald, F.J. Kruger & A.A. Ferrar), pp. 239-246. Oxford
University Press, Cape Town.
Using computer technology in fire management: an example from the mountain catchment areas of the Cape Province
- D M Richardson
- B W Van Wilgen
- D C Le Maitre
- K B Higgins
- G G Forsyth
Richardson, D.M., van Wilgen, B.W., Le Maitre, D.C., Higgins, K.B. & Forsyth, G.G. (1994) Using computer technology in fire management: an example from the mountain
catchment areas of the Cape Province, South Africa. International Journal of Wildland Fire, 4, 17-32.
Report on the problems relating to the fire site on Devil's Peak and proposals toward their solution
- D F Scott
- D C Le Maitre
- B W Van Wilgen
Scott, D.F., Le Maitre, D.C. & van Wilgen, B.W. (1991)
Report on the problems relating to the fire site on Devil's
Peak and proposals toward their solution. Report C-72,
CSIR Division of Forest Science and Technology, Pretoria.
Ecosystem management. The Ecology of Fynbos: Nutrients, Fire and Diversity Fuel properties of vegetation in Swartboskloof
- B W Wilgen
- W J Bond
- D M Richardson
- R M Ed
- B W Cowling
- H J Van Hensbergen
Impacts of invasive
plants on water
resources
van Wilgen, B.W., Bond, W.J. & Richardson, D.M. (1992)
Ecosystem management. The Ecology of Fynbos: Nutrients, Fire and Diversity (ed. R.M. Cowling), pp. 345-371.
Oxford University Press, Cape Town.
van Wilgen, B.W. & van Hensbergen, H.J. (1992) Fuel
properties of vegetation in Swartboskloof. Fire in South
African Mountain Fynbos. Species, Community and Ecosystem Response in Swartboskloof (eds B.W. van Wilgen,
D.M. Richardson, F.J. Kruger & H.J. van Hensbergen),
pp. 37-53. Springer-Verlag, Heidelberg.
van Wyk, D.B. (1987) Some effects of afforestation on
streamflow in the western Cape Province, South Africa.
Water SA, 13, 31-36.
The effects of fire on soil water repellency, catchment sediment yields and streamflow. Fire in South African Mountain Fynbos: Species, Community and Ecosystem Response in Swartboskloof
- D F Scott
- D B Van Wyk
Scott, D.F. & van Wyk, D.B. (1992) The effects of fire on
soil water repellency, catchment sediment yields and
streamflow. Fire in South African Mountain Fynbos:
Species, Community and Ecosystem Response in Swartboskloof (eds B.W. van Wilgen, D.M. Richardson, F.J. Kruger
& H.J. van Hensbergen), pp. 216-239. Springer-Verlag,
Heidelberg.
van der Zel, D.W. & Kruger, F.J. (1975) Results of the
multiple catchment experiments at the Jonkershoek
Research Station, South Africa. II. Influence of protection
of fynbos on stream discharge in Langrivier. Forestry in
South Africa, 16, 13-18.