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Invasive alien plants and South African rivers: A proposed approach to the prioritization of control operations
Abstract
1. A number of parallel initiatives in South Africa have been addressing the prioritization and management of invasive alien plant species, the prioritization of rivers for the conservation of biodiversity, and broad-scale planning for water resource management. This paper has combined aspects of these approaches to develop a composite index of prioritization of quaternary catchments for alien plant control purposes.
2. We calculated, for each quaternary catchment, a simple composite index that combined estimates of (i) the number of invasive alien plant species present; (ii) the potential number of invasive alien plant species that would be present if they occupied the full range as determined by climatic envelope models; (iii) the degree of habitat loss in rivers; and (iv) the degree of water stress. Each of the four components contributed between one and four to the combined index, which had a range of values between four and 16.
3. We used a geographic information system to map the distribution of priority catchments for invasive alien plant control. Of the 1911 quaternary catchments in South Africa and Lesotho, just over one-third (650) were in the highest priority category with an index of 13 or more. A relatively small proportion (273, or 14%) of the catchments had the maximum scores of 15 or 16.
4. The approach identified priority areas that have not currently been identified as such, and should provide decision makers with an objective and transparent method with which to prioritize areas for the control of invasive alien plants. We anticipate debate about the way in which components of the index are calculated, and the weight given to the different components, and that this will lead to the transparent evolution of the index. Improvements would also come about through the addition of a more comprehensive list of species, and through the addition of further components.
... Transformer species were defined as the "subset of invasive plant species that change the character, condition, form, or nature of ecosystems over a substantial area relative to the extent of that ecosystem" (Richardson et al. 2000, McGeoch et al. 2006. From the overall SANParks species list we extracted those species that we considered transformers using information from four key publications, (i) Henderson (2001), declared alien weeds and invasive plants, (ii) Nel et al. (2004), a classification of invasive alien plant species in South Africa, (iii) van Wilgen et al. (2008a), a biome scale assessment of the impact of invasive alien plants, and (iv) van Wilgen et al. (2008b) prioritising species and catchments for guiding invasive alien plant management in South Africa). We also considered national legislation that regulates the management of alien and invasive plants in South Africa (CARA; Conservation of Agricultural Resources; Act 43 of 1983, as amended 2001). ...
... Rivers have been widely acknowledged as key dispersal vectors for invasion (Richardson et al. 2007, Esler et al. 2008, Naiman and Décamps 1997, van Wilgen et al. 2007) and more than 60% of the species in our list can disperse along rivers. Propagules transported by water flow can be widely dispersed during floods, and riparian zones and rivers banks provide highly suitable habitat (Alpert et al. 2000). ...
... Propagules transported by water flow can be widely dispersed during floods, and riparian zones and rivers banks provide highly suitable habitat (Alpert et al. 2000). Surveillance activities along rivers should be flagged as a priority area to detect new species and changes in distribution (van Wilgen et al. 2007, Forsyth et al. 2012. Trees and tree-shrubs, which are likely to be more conspicuous and easier to detect, comprise only just over half of the list, suggesting that increased effort needs to be made to detect less visible species. ...
Protected areas face mounting pressures, including invasion by alien plant species. Scientifically sound information is required to advise invasive species management strategies, where early detection and rapid response is particularly important. One approach to this is to determine: (i) the relative importance of pathways of invasion by which a species is introduced, (ii) the range of likely impacts associated with each species, and (iii) the relationship between pathways and impacts, to assess the relative threats posed by different pathways of alien species introductions. This assessment was performed on 139 alien plants that are invasive across the South African National Parks (19 national parks, covering ~39,000 km ² ), and based on available literature and expert opinion, known to have negative ecological impacts. For each species the likelihood of being introduced by each of eight pathways, and of having negative impacts in each of 13 identified impact categories, was assessed. The similarity of impact and pathway types between species was assessed using the Jaccard index and cladograms. Differences in the prevalence of impacts and pathways and relationships between these were assessed using a Chi-squared contingency and Generalised Linear Model. Nearly 80% of the species are ornamental plants and about 60% are also dispersed by rivers, highlighting the importance of managing ornamental species and surveillance along rivers in preventing future invasions. As to the impacts, ~95% of the species compete directly with native species and 70% change the physical structure of the environment. The majority of species exert multiple impacts, with 70% of species assessed having five or more impacts. There was a significant positive relationship between the number of pathways via which a species can be introduced into an area and the number of potential impacts they can have. This suggests that species using multiple pathways reach a wider range of suitable habitats, increasing the potential for different kinds of impacts over a wider area.
... In South Africa, the strategy over the past 15 years has been to implement a large, national-scale, government-sponsored alien plant control program (van Wilgen et al., 1998(van Wilgen et al., , 2011aKoenig, 2009). Known as 'Working for Water', the program has adopted a comprehensive approach to alien plant control, characterised by several distinguishing features. ...
... When South African ecologists first argued for government funding to address the problem of invasive alien plants, their focus was on reducing ecological impacts, notably on water resources. By placing a monetary value on an ecosystem service (rather than on conservation per se), they demonstrated that such an investment would deliver value by protecting the resources vital for development (van Wilgen et al., 1998). The fact that the work could be carried out in a labour-intensive way, thereby creating much-needed employment, was seen as an additional benefit. ...
... Working for Water's strategic plan (Anonymous, 2007) calls for, among other things, the prioritisation of invasive alien plant species for management action, the development of indicators to underpin a monitoring program, and the implementation of such a program. A start has been made with prioritisation (Nel et al., 2004;van Wilgen et al., 2007van Wilgen et al., , 2008bRoura-Pascual et al., 2009), but monitoring and evaluation have not been adequately resourced to date. The ongoing attempts to control a wide range of invasive alien plant species in the absence of adequate co-ordination and monitoring has been described as ''a strategy of hope'' (van Wilgen et al., 2011b). ...
... In South Africa, the strategy over the past 15 years has been to implement a large, national-scale, government-sponsored alien plant control program (van Wilgen et al., 1998(van Wilgen et al., , 2011aKoenig, 2009). Known as 'Working for Water', the program has adopted a comprehensive approach to alien plant control, characterised by several distinguishing features. ...
... When South African ecologists first argued for government funding to address the problem of invasive alien plants, their focus was on reducing ecological impacts, notably on water resources. By placing a monetary value on an ecosystem service (rather than on conservation per se), they demonstrated that such an investment would deliver value by protecting the resources vital for development (van Wilgen et al., 1998). The fact that the work could be carried out in a labour-intensive way, thereby creating much-needed employment, was seen as an additional benefit. ...
... Working for Water's strategic plan (Anonymous, 2007) calls for, among other things, the prioritisation of invasive alien plant species for management action, the development of indicators to underpin a monitoring program, and the implementation of such a program. A start has been made with prioritisation (Nel et al., 2004;van Wilgen et al., 2007van Wilgen et al., , 2008bRoura-Pascual et al., 2009), but monitoring and evaluation have not been adequately resourced to date. The ongoing attempts to control a wide range of invasive alien plant species in the absence of adequate co-ordination and monitoring has been described as ''a strategy of hope'' (van Wilgen et al., 2011b). ...
... thickets seem to flourish in areas with high water availability throughout South Africa. Widespread invasion of ephemeral river systems by the IAP is responsible for large-scale depletion of groundwater (Van Wilgen et al., 2007). According to the Department of Water Affairs (2013), IAPs are responsible for the 695 million m 3 of annual reduction in the water supply of dams and river systems in South Africa. ...
... Mapping the extent of IAPs is essential to improving the understanding of management initiatives in terms of planning and implementation (Shackleton et al., 2014). Mapping techniques help improve planning procedures to prioritise the areas identified for the clearing of IAPs (Van Wilgen et al., 2007, Rouget et al., 2004. Van Wilgen et al. (2012) indicated that only 4% of Prosopis spp. in the estimated total invaded area throughout South Africa was cleared in all the arid biomes despite 435 million Rands spent. ...
Invasive alien plants (IAPs) are responsible for loss in biodiversity and the depletion of water resources in natural ecosystems. Prosopis species are IAPs previously introduced by farmers to provide shade and fodder for livestock. In the Northern Cape, Prosopis spp. invasions are associated with the loss of native species resulting in overgrazing and degrading rangelands. Mapping Prosopis glandulosa is essential for management initiatives to assist the government in minimising the spread and impact of IAPs. This study aims to evaluate the performance of two machine learning algorithms i.e., Support Vector Machine (SVM) and Random Forest (RF) to map the spatial dynamics of P. glandulosa in Prieska. The spatial invasion extent of P. glandulosa was mapped using multitemporal Landsat data spanning the period from 1990 to 2018. Validation of the results was done through an estimated error matrix with the use of the proportion of area and the estimates of overall accuracy, user's accuracy and producer's accuracy with a 95% confidence interval. The performance of the SVM and RF classifiers showed similar results in the overall accuracy and Kappa statistics throughout the years. These methods showed an overall increase of at least 3.3% of the area invaded by P. glandulosa from 1990 to 2018. The study indicates the importance of Landsat imagery for mapping historical and current land cover change of IAPs. The spread of P. glandulosa was confirmed by an increase in the total area of invasion, which enables decision-makers to improve monitoring and eradication initiatives.
... 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). However, the prioritisation of areas for management intervention is sensitive to the weighting of component factors, objectives and the availability of information . ...
... Over time, the sustainability of the strategy is undermined as the surrounding landscape is impacted by invasion, perpetuating the need for repeat clearing in the waterways as propagules reinvade from outside (Vardien et al., 2012). While it is unlikely that Water production would be used as a primary strategy in conservation areas, this strategy is commonly promoted at larger scales (van Wilgen et al., 2007;Forsyth et al., 2012). ...
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.
... South Africa is a dry country, and like many others the demand for water resources often exceeds the capacity of ecosystems to provide them. While the country as a whole still has a water surplus, recent studies have shown that demand already exceeds supply in more than half of the 87 water management areas in South Africa (van Wilgen et al., 2007). Thus, any further reduction in water supplies as a result of watershed areas becoming invaded by trees and shrubs will seriously retard the prospects for economic growth. ...
... We have not attempted to address this issue here, but the dataset created as part of this project could feed into decision-support products developed for this purpose. For example, van Wilgen et al. (2007) used data on the distribution and impacts of alien plants to examine where such priorities should lie. Their approach identified priority areas that had not been identified as such, and predicted that their approach would provide decision-makers with an objective and transparent method with which to prioritise areas for the control of invasive alien plants. ...
... It was deliberately introduced into South Africa in the late 1700s, primarily for erosion control (Guthrie 2007). The reed spread throughout the country as vegetative growth was facilitated by anthropogenic activities, including building of dams and soil stabilization; it has since become one of the worst invasive alien species in the country and is now present in all nine provinces (Guthrie 2007; Van der Merwe et al. 1990;van Wilgen et al. 2007). The reed has been listed as a Category 1 invasive alien species according to the National Environmental Management: Biodiversity Act (NEMBA, Act No. 10 of 2004) (Henderson 2001;van Wilgen et al. 2007). ...
... The reed spread throughout the country as vegetative growth was facilitated by anthropogenic activities, including building of dams and soil stabilization; it has since become one of the worst invasive alien species in the country and is now present in all nine provinces (Guthrie 2007; Van der Merwe et al. 1990;van Wilgen et al. 2007). The reed has been listed as a Category 1 invasive alien species according to the National Environmental Management: Biodiversity Act (NEMBA, Act No. 10 of 2004) (Henderson 2001;van Wilgen et al. 2007). Category 1 plants are prohibited from being sold or planted, and additional efforts are needed to keep the plant under control (Henderson 2001). ...
The giant reed, Arundo donax is one of the worst invasive alien species globally, including South Africa, where it invades riparian areas across the country. Biological control is being considered to address the invasive potential and negative impacts of the weed. This study investigated the phylogeography of A. donax to guide the biological control program. To determine plant haplotype and genetic diversity, three regions of the chloroplast were sequenced and three microsatellite markers were analyzed in 40 samples from across the plant’s distribution in South Africa. It was determined that all populations of A. donax in South Africa were haplotype M1, which is the most widely distributed haplotype worldwide, believed to originate from the Indus Valley, Asia. In addition, no genetic diversity was found, indicating that all the A. donax populations in South Africa are essentially one clone. The results indicate that suitable biological control agents are likely to be found in the ancient native range of haplotype M1. This research has contributed to the global understanding of the phylogeography of A. donax and will guide the biological control program in South Africa.
... Our knowledge of biological invasions has been strongly influenced by ongoing developments in the South African research environment. In Figure 12.1 The CfR catchments are the most invaded in the country in terms of the species richness of major ecosystem transformers that affect water resources (van Wilgen et al. 2007). The number of species recorded per catchment is shown for thirteen species (acacia mearnsii; arundo donax; Eucalyptus camaldulensis; Hakea sericea; Hakea gibbosa; Nerium oleander; Pinus patula; Pinus pinaster; Pinus radiata; Populus canescens; Prosopis glandulosa; Salix babylonica; Tamarix chinensis.) ...
... Several research projects were undertaken and tools developed to give effect to the strategy, such as the development of a spatial decision support tool for prioritization and scheduling of invasive alien plant interventions (Roura-Pascual et al. 2009) and the prioritization of species and primary catchments for the purposes of guiding the invasive plant operations in the terrestrial biomes of South africa (van Wilgen et al. 2007). ...
... As noted previously, several methods have been used to remove water hyacinth from water bodies, including mechanical dredging using machinery, in-situ cutting, chemical control, manual harvesting, and biological control [13], [19], [21], [35]- [37], [41], [123]. Challenges faced by current water hyacinth control efforts, particularly the high economic cost of mechanical removal and the rapid reinvasion of reclaimed water bodies by the weed has been highlighted [16], [124]. ...
... Many evidence-based approaches for prioritizing sites have been developed for IAP taxa at various spatial scales, for example, in protected areas (Tu, 2009), and quaternary and primary catchments (Forsyth et al., 2012;van Wilgen et al., 2007). However, there are few broadly adopted, standardized approaches for prioritizing sites sensitive to alien plant invasions in urban areas, despite their potential for improving management planning in these complex socio-ecological landscapes. ...
Rapid urbanization is placing increased pressure on natural, restored and designed ecosystems to provide services to growing human populations. The establishment and spread of invasive alien species within and around urban areas threaten biodiversity and ecosystem functioning, and the services they provide. Consequently, there is a need to protect and manage areas where invasions will have the greatest socio‐ecological impact. Limited resources call for the strategic prioritization of these areas, yet there are few widely adopted, standardized approaches for prioritizing sites vulnerable to species invasions in urban areas.
We applied multi‐criteria decision analyses in a geographic information system to develop a strategic, spatial prioritization approach for identifying those sites most sensitive to terrestrial alien plant invasions. To test this approach, we use the Toronto region as a case study, the most populous metropolitan area in Canada and one of the fastest growing urban centres in North America. Through consultation with local conservation authorities, we developed an objective, hierarchical set of 19 criteria grouped into two categories: biodiversity and ecosystem functioning, and ecosystem services. Spatial data layers were assigned to each criterion and used to map areas most important for biodiversity and ecosystem functioning and providing ecosystem services. We overlayed these priority areas with distribution data of Vincetoxicum rossicum, one of the Toronto region's most widespread and damaging invasive alien plant species (IAPs) to determine the potential threat species’ invasions pose to these important areas.
High‐priority sites identified by our prioritization model include areas of significant biodiversity conservation value such as intact forests, meadows and wetlands which are crucial for providing regulating and supporting services. Our IAPs distribution map showed that these high‐priority sites are heavily invaded (92.9% of the area occupied by V. rossicum comprises medium‐high‐priority sites) and should be prioritized for management to ensure biodiversity and ecosystem functioning and the provision of ecosystem services are maximized.
The approach applied in this study can be useful for conservation practitioners in guiding the selection of high‐priority, socio‐ecologically significant sites for management action in urban landscapes across different geographic regions and spatial scales.
... The catchment-scale biomonitoring field surveys and modeling studies could detect multiple pressures on freshwater ecosystems, especially in critically essential aspects of river connectivity (longitudinal and vertical) [63,69]. To adequately control the menace of IAFS, multi-zonal plans at the catchment level could help recognize the critical priority areas at local to regional levels. ...
Invasive alien fish species (IAFS) influence recipient ecosystems in multiple ways, from altered native fish communities to poor ecological health and higher economic losses to control and eradication. We tested key drivers and connections between an IAFS (Micropterus salmoides) presence, absence, geomorphological, hydro-chemical, physical habitat, native fish assemblages, and large river basins biotic integrity during 2016–2019. A total number of 62,121 individuals (TNI) representing 74 fish species were observed, out of which 68 species (45,677 TNI) belonged to the Geum River (GR) basin, while 63 species (16,444 TNI) were from the Mankyong/Dongjin River (MDR) basin. The results illustrated a significant contrast based on stream order, catchment area, altitude, stream gradient, and width among the sites with and without largemouth bass. However, fluctuations in nutrients (nitrogen and phosphorus) were not affected by variations in pH, dissolved oxygen, conductivity, suspended solids, and river flow. The largemouth bass has emerged as the 8th largest fish population in the GR and swiftly occupies the MDR basin with a constancy value of 45.5. Native sensitive (r = −0.38), insectivore (r = −0.252), carnivores (r = −0.085), and TNI (r = −0.512) displayed a negative correlation with increasing largemouth bass abundance. Largemouth bass induced significant regime transformation in the carnivore species. A significant difference (p < 0.01) of biotic integrity was illustrated among the largemouth bass population sites. A conspicuous interplay between ‘poor’ ecological health (r = 0.33, p = 0.038, n = 41) sites and ‘fair–excellent’ (r = −0.38, p < 0.001, n = 622) sites as compared to the overall ecological health linked with largemouth bass abundance (r = −0.397, p < 0.001, n = 663) alluded to stronger impact of the IAFS. In conclusion, the largemouth bass has potentially altered the native fish assemblage and ecological health. Further, we conclude that rapidly shifting flow patterns supported by the expanding anthropogenic interventions (weirs and dam) are the most approving factors of impending fish invasions.
... It was recommended that investment be made to develop strategies to prioritise the selection of projects and to invest 'a portion of funds into the prioritisation of control operations, planning, monitoring and evaluation' . There have been efforts to address this shortfall with a number of prioritisation initiatives that outline transparent and systematic approaches to guide the decision-making of which IAPs to manage, the type of control and which areas to target in South Africa (see Forsyth et al., 2009;Forsyth et al., 2012;Hoeneisen, 2013;Le Maitre & Forsyth, 2010;Macdonald & Jarman, 1985;Nel et al., 2004;Robertson et al., 2003;Roura-Pascual et al., 2009;Van Wilgen et al., 2007, 2008. ...
Biological control is an effective and sustainable method for management of invasive alien plants (IAPs), and has been implemented on 68 of the 367 plant species that are listed as legally requiring management strategies under South Africa’s National Environmental Management: Biodiversity Act (10/2004): Alien and Invasive Species Regulations. With limited resources and funding available, it can realistically only be considered for a subset of the remaining alien plants for which biocontrol has not yet been implemented. Considerable funding has been allocated towards biocontrol in South African in the past, principally through the Working for Water Programme of the Nature Resource Management Programmes (Department of Environment, Forestry and Fisheries), and this support is expected to continue with the intention of increasing the number of IAPs under this management approach in the future. To ensure appropriate targets are selected, the Biological Control Target Selection (BCTS) system was applied to the alien plants on this list that are not under biocontrol (299 species). This paper presents the resultant list of top priority species that represent good investments for biocontrol when funds are available.
... Indeed, a higher post-fire growth rates of A. donax (three to four times faster than other native riparian plants), high growth rate, and growth response to nutrient enrichment are further increasing the susceptibility of riparian woodland to giant reed establishment (Coffman et al. 2010). This species becomes a major problem in different world countries such as in Mexico, South Africa, and parts of the United States, especially California, Arizona, and Texas, and in particular the Santa Ana River basin and Rio Grande basin (Milton 2004;Van Wilgen et al. 2007). A. donax is gradually threatened aquatic ecosystems across Iraq. ...
Identification of invasive alien plant species and their pathways is important to manage and control these species and also to prevent their introduction. Invasion of local habitat by alien species is alarming the Iraqi environment. There is a real action regarding invasive alien species at the global level, while in Iraq the case still has less concern within the scientific community. The national monitoring program is needed to control invasive alien species, through conducting further investigation and field surveys on such species, including their impact and distribution across Iraq. Preventing the introduction of invasive alien species at border points, eliminate the damage caused by the introduction, except for studies purposes with the restricted regulation, and eradication of the invasive species through intensive cooperation between the relevant associations and bodies with the natural resources. This chapter is an attempt to give the status of invasive alien species in Iraq to create a solid platform for establishing a strategic plan to treat these plant species. Part of the alien species available now in Iraq are gradually threatening aquatic ecosystems across Iraq. Many invasive species are clarified here having the exceeded uses of resources that force out native plant species in their habitats. New plant species with the invasion habits and wide distribution in Iraq are also stated for the first time in this publication. Some of these alien species are characterized with high salinity resistance and exceeded the rate of heavy metals, such as Arundo donax and Phragmites spp. Others with wide genetic bases highly resist the fluctuated environmental condition due to introgression and wider hybridization such as Imperata cylindrica and Tamarix spp. Industrial and medicinal uses of some the alien plant species are also among their advantages. Despite these beneficial uses of few alien species, the majority behave as invaders to local habitats and environments, due to their genetic architecture to compete with native plant species for the water and resources such as Brassica tournefortii, Centaurea solstitialis and Rumex crispus. Others could increase the risk of forest fire due to high biomass products such as Hypericum perforatum and Salsola tragus. A big attempt has to be challenged to minimize the impacts of existing populations from these invaders before stepping worse predation. New policies must be prioritized to regulate and managing invasive plant species in Iraq with the intensive involvement of the government in the sustainable management of plant invaders. Innovative regulations have to be followed in the introduction of plant species to prevent extra invasion. This progress should be paralleled with the management and eradication of the identified invasive species.
... There are reports from the developing world (e.g., Kateregga and Sterner, 2007) that prevalence of known drivers of invasiveness (e.g., levels of disturbance [Godefroid, 2001]) and indicators of alien plant impacts should be considered in such an exercise (Gaertner et al., 2009;Hejda et al., 2009). A few studies have also attempted to develop indices of invasiveness to prioritise riparian zones for alien plant eradication and control in rapidly urbanising countries such as South Africa (e.g., van Wilgen et al., 2007), but this has not been applied across biomes/habitat types. This is due to the complexity of dealing with issues around invasion biology, such as the lack of alien distribution data in developing cities, levels of transformation, and urban heterogeneity, amongst others. ...
Urban natural green spaces are becoming increasingly impacted by anthropogenic disturbances, promoting alien plant invasions. Using a rapidly developing city in South Africa as a case study, we related distribution, composition, and ordering of alien plant species to environmental and anthropogenic factors to identify drivers of invasiveness. Vegetation surveys were used to identify and quantify (in terms of composition and density) alien species within 30 natural green spaces. Floristic characteristics were then related to levels of non-natural disturbance and selected abiotic parameters. Based on the relationships observed, selected floristic parameters were used to develop an Alien Invasive Index to identify ‘invasive alien hotspots’. Collectively, 80 alien plant species (from 30 families) were found, 35 of which are invasive. The most speciose families were Asteraceae > Fabaceae > Verbenaceae. Their representatives, specifically the invasive shrubs Lantana camara (Verbenaceae) and Chromolaena odorata (Asteraceae) and alien herbs Conyza sumatrensis, Bidens pilosa and Tagetes minuata (Asteraceae) were also the most dominant in terms of frequency across sites and density. A Principal Component Analysis showed invasive alien plant species composition to be most strongly related to level of disturbance, followed by distance to informal settlement and soil moisture content. The Alien Invasive Index could discriminate between sites with low and high levels of invasiveness, and its suitability was validated by the fact that sites with very high index values were in close proximity to informal settlements. The study demonstrates the value of combining classical in situ vegetation surveys and overlay analysis using Geographic Information System for prioritising green spaces and alien species for management in cities that are limited in terms of financial resources.
... The EWG also notes that, reciprocally, community composition itself can influence fire dynamics (Mandle et al., 2011). Hakea sericea has been identified as influencing fire regimes both positively and negatively (Mandle et al., 2011), increasing fuel loads and intensity, but decreasing spread and frequency (van Wilgen & Richardson, 1985;Holmes et al., 2000;van Wilgen et al., 2007). In France, the legal requirement for brush cutting as a measure of fire protection, helps the spread of H. sericea (K. ...
... Several approaches to finerscale prioritization have been described (e.g. Margules and Pressey 2000, Noss et al. 2002, Groves 2003, Strager and Rosenberger 2006, van Wilgen et al. 2007, Wilhere et al. 2008). This paper builds on that body of work to identify areas in need of immediate conservation action in the Gulf. ...
Identifying priority areas for conservation is a widely-used approach to allocate limited resources to achieve desired conservation outcomes. While selection algorithms have become popular methods for designing networks of conservation areas, support is often insufficient to protect all proposed sites. A recent ecoregional assessment in the Gulf of California identified critical conservation sites to protect biodiversity in this region. Here we build on this foundation of conservation planning work to identify a path forward from conservation prioritization to conservation action, bringing conservation priorities to a management scale. We prioritize areas for conservation action at two scales (within and among sites) using a combination of conservation planning tools, including: 1) a transparent approach that relies on the comparison of irreplaceability and vulnerability scores among the 54 conservation sites, and 2) expert opinion in distilling biodiversity goals into eight habitat targets that represent biodiversity. Irreplaceability of each conservation target was given a distinct score based on the conservation status, endemism, and critical life stages of each species. A threat score was estimated from expert surveys for each target to assess vulnerability. Our analyses can be used to identify priority sites, depending on level of risk-aversion and preferences for vulnerable or irreplaceable conservation targets, and to prioritize small-scale areas within sites. We discuss key lessons learned that could be easily applied to other conservation planning problems.
... For example, Brown & Whelan (1999), studying H. sericea in its native Australia in the context of fire seasonality and community diversity, found that fire too early in the fruit ripening process could reduce the supply of viable seeds due to the unripe fruits still containing enough moisture to make heating lethal to young tissue. Hakea sericea has been identified as influencing fire regimes both positively and negatively (Mandle et al., 2011), increasing fuel loads and intensity, but decreasing spread and frequency (Van Wilgen & Richardson, 1985;Holmes et al., 2000;van Wilgen et al., 2007). ...
Data sheets on pests recommended for regulation
... The forest plants that die in the process also increase fuel loads, which, combined with drier and windier edge conditions, create an environment increasingly favourable for fire disturbance. Whether from lightning strikes or human activities, subsequent fires burn hotter and over a larger area (van Wilgen et al., 2007), disturbing and destroying more and more habitat each time. Through these mechanisms, edge effects can degrade entire ecosystems over time, harming both the native species and human livelihoods that depend on those areas. ...
Conservation Biology in Sub-Saharan Africa comprehensively explores the challenges and potential solutions to key conservation issues in Sub-Saharan Africa.
Easy to read, this lucid and accessible textbook includes fifteen chapters that cover a full range of conservation topics, including threats to biodiversity, environmental laws, and protected areas management, as well as related topics such as sustainability, poverty, and human-wildlife conflict. This rich resource also includes a background discussion of what conservation biology is, a wide range of theoretical approaches to the subject, and concrete examples of conservation practice in specific African contexts. Strategies are outlined to protect biodiversity whilst promoting economic development in the region.
Boxes covering specific themes written by scientists who live and work throughout the region are included in each chapter, together with recommended readings and suggested discussion topics. Each chapter also includes an extensive bibliography.
Conservation Biology in Sub-Saharan Africa provides the most up-to-date study in the field. It is an essential resource, available on-line without charge, for undergraduate and graduate students, as well as a handy guide for professionals working to stop the rapid loss of biodiversity in Sub-Saharan Africa and elsewhere.
... Some of the most effective pest control programmes use an integrated pest management (IPM) approach that relies on using multiple pest control methods described above either simultaneously or in succession (van Wyk and van Wilgen, 2002). Strategic planning to coordinate best practices can also help offset some of the costs of invasive species control (Rahlao et al., 2010) and ensure that important pest sources are not missed (van Wilgen et al., 2007). When considering the best method to control an invasive species, it may also help to consider how our own actions inadvertently encourage invasive species. ...
Conservation Biology in Sub-Saharan Africa comprehensively explores the challenges and potential solutions to key conservation issues in Sub-Saharan Africa.
Easy to read, this lucid and accessible textbook includes fifteen chapters that cover a full range of conservation topics, including threats to biodiversity, environmental laws, and protected areas management, as well as related topics such as sustainability, poverty, and human-wildlife conflict. This rich resource also includes a background discussion of what conservation biology is, a wide range of theoretical approaches to the subject, and concrete examples of conservation practice in specific African contexts. Strategies are outlined to protect biodiversity whilst promoting economic development in the region.
Boxes covering specific themes written by scientists who live and work throughout the region are included in each chapter, together with recommended readings and suggested discussion topics. Each chapter also includes an extensive bibliography.
Conservation Biology in Sub-Saharan Africa provides the most up-to-date study in the field. It is an essential resource, available on-line without charge, for undergraduate and graduate students, as well as a handy guide for professionals working to stop the rapid loss of biodiversity in Sub-Saharan Africa and elsewhere.
... Arundo donax was deliberately introduced in the late 1700s, and was used for a wide range of purposes most notably for erosion control (Bell, 1997;Henderson, 2001). Arundo donax has since become one of the worst IAS in the country and is listed as a Category 1 species according to the National Environmental Management: Biodiversity Act (NEMBA) (Act No 10 of 2004) which prohibits it from being sold or planted and suggests that control efforts are required (Henderson, 2001;van Wilgen et al., 2007). Despite the threat A. donax poses to South Africa's biological diversity, very few baseline data are available to guide management. ...
The Enemy Release Hypothesis (ERH) predicts that introduced plant species can escape herbivory and therefore have a competitive advantage over native plants, which are exposed to both generalist and specialist natural enemies. In this study, the ERH was explored using the invasive alien species, Arundo donax and two native tall-statured grasses, the cosmopolitan Phragmites australis and African endemic Phragmites mauritianus in South Africa. It was predicted that A. donax would have reduced species richness of herbivores compared with the native Phragmites spp., that it would be devoid of specialist herbivores and would thus be experiencing enemy escape in the adventive range. The herbivore assemblages were determined from both field surveys and a literature review. The assumptions of the ERH were for the most part not met; 13 herbivores were found on A. donax compared with 17 on P. australis and 20 on P. mauritianus. Arundo donax had two specialist herbivores from its native range, and shared native herbivores with Phragmites spp. Although A. donax had reduced species richness and diversity compared with that found in the native distribution, it has partially re-acquired a herbivore assemblage which is similar to that found on analogous native species. This suggests that enemy release may not fully explain the invasive success of A. donax in South Africa.
... At the national scale, we confirmed the prevailing importance of climatic variables with respect to land cover and anthropogenic factors. Moreover, we found out that overall the newly potentially invaded QCs are much less than the currently invaded ones, therefore control operations should focus on managing the density of priority IAPS within their current range (see Van Wilgen et al. 2007), rather than preventing the expansion of the distribution . This type of approach should necessarily be accompanied with finer scale analysis to identify local components of the problem so that the control operations can be structured as efficiently as possible. ...
Alien plants invasion has negative impacts on the structure and functionality of ecosystems. Understanding the determinants of this process is fundamental for addressing environmental issues, such as the water availability in South Africa’s catchments. Both environmental and anthropogenic factors determine the invasion of alien species; however, their relative importance has to be quantified. The aim of this paper was to estimate the importance of 32 explanatory variables in predicting the distribution of the major invasive alien plant species (IAPS) of South Africa, through the use of Species Distribution Models. We used data from the National Invasive Alien Plants Survey, delineated at a quaternary catchment level, coupled with climatic, land cover, edaphic, and anthropogenic variables. Using two-part generalized linear models, we compared the accuracy of two different sets of variables in predicting the spatial distribution of IAPS; the first included environmental correlates alone, and the second included both environmental and anthropogenic variables. Using Random Forest, we explored the relative importance of the variables in producing a map of potential distribution of IAPS. Results showed that the inclusion of anthropogenic variables did not significantly improve model predictions. The most important variables influencing the distribution of IAPS appeared to be the climatic ones. The modeled potential distribution was analyzed in relation to provinces, biomes, and species’ minimum residence time.
... There is however significant invasion of alien plant species (primarily Pinus pinaster (Mediterranean cluster pine) and Hakea sericea (silky hakea)) in these mountains (e.g. van Wilgen et al. 2007), particularly on the Riviersonderend Mountain range (Le Maitre et al. 2002) where A. atermina occurs. Continued control of the invasive alien plants is required to preserve the hydrological function of the mountain seeps and to protect Arthroleptella and other species from the increased heat that results when fires burn areas invaded by woody plants such as pines. ...
A comprehensive survey of the Cape Fold Mountains, South Africa, was undertaken for moss frogs of the genus Arthroleptella. Advertisement calls were recorded and voucher specimens collected for all populations encountered. A molecular phylogeny was constructed for the entire genus using two mitochondrial and one nuclear marker. Standard morphological measurements were made and salient morphological characters described. Analysis of these data revealed the presence of three undescribed species: two that were previously obscured under Arthroleptella bicolor and one obscured under A. landdrosia are described herein. The advertisement calls of the three new species are described and contrasted with the calls of other Arthroleptella species. Their distribution is described and spatial extent of occurrence quantified along with a brief discussion of conservation status for each species.
ZooBank.—Arthroleptella draconella: urn:lsid:zoobank.org:act:341BABC2-63A8-4C60-A306-D232E92ECE69
Arthroleptella atermina: urn:lsid:zoobank.org:act:AC23D804-3075-40DB-9852-624C32A51547
Arthroleptella kogelbergensis: urn:lsid:zoobank.org:act:AA573B06-BA81-4B84-B436-5F5CCDF1D892.
... Length ( (Van Wilgen et al., 2007, which was successfully done in the IASP program. A large part of the success of C. odorata control in HiP can be attributed to accurate prioritization of clearing efforts in relation to fire and close collaboration between clearing operations, park management, and research. ...
Biological invasions have increased dramatically in the past centuries and are one of the greatest threats to biodiversity today. Chromolaena odorata, a herbaceous shrub from the Americas, is one of the most widespread and problematic invasive plant species in the tropics and sub-tropics. The plant is a serious problem in South Africa, where invasive species threaten biodiversity and use up water resources. This study combines data on the distribution of C. odorata with ecological and clearing management data to evaluate the efficacy of an invasive plant clearing program over its decade of operation in the Hluhluwe-iMfolozi Park in KwaZulu-Natal, South Africa. Densities and local extent of the C. odorata invasion were significantly reduced during the period of operations of the clearing program. Seasonal effects impacted clearing efficacy, namely a reduction in efficacy during the seed dispersal period. Clearing success was positively associated with clearing effort and fire frequency and negatively associated with rainfall. Management implications drawn from the results include halting clearing during the seed-drop period, giving extra attention to areas with more rainfall and other water availability, and incorporating fire with other clearing methods where possible.
... Giant reed has naturalized in numerous countries, where in many places its impact appears to be localized and minor. However, it is considered to be a major problem in South Africa, Mexico, and parts of the United States, especially California, Arizona and Texas, and in particular the Santa Ana River basin and Rio Grande basin (Van Wilgen et al. 2007 ). Arundo was originally imported into North America perhaps as early as the 1500s by the Spanish (as a source of fi bre) (USDA 2008 ). ...
Selenium (Se) is an essential micronutrient for humans, animals and some lower plants at very low concentrations, whereas it is extremely toxic at higher doses. Furthermore, living organisms become exposed to high Se concentrations via both anthropogenic and natural releases of Se to the environment. Thus, Se may be released naturally into soils formed from Se-bearing shales. Hence, this in turn can lead to the production of large quantities of Se-contaminated irrigation and drainage water. About the anthropogenic sources of Se, they include coal ash leachates or mining production, aqueous discharges from electric power plants, industrial wastewater and oil refinery industry. In general, Se levels in most soils are very low (0.44 mg kg⁻¹) and naturally Se occurs in certain Cretaceous shale sediments. Furthermore, seleniferous soils contain up to 100 mg kg⁻¹ Se, and when fossil fuels derived from these soils are used, or when these soils are cultivated, toxic levels of Se may accumulate in the environment. Hence, using of Se hyperaccumulator plants can be thrived on seleniferous soils, providing another portal for Se into the agroecosystem. These plants could be alleviated both of these problems, either as a source of dietary Se or for phytoremediation of excess Se from the environment. On the other hand, these plants also have the ability to clean up agricultural soils and industrial wastewaters, due to their capacity to not only take up and then accumulate Se but also convert inorganic Se into volatilized forms that are released into the atmosphere.
... Invasive alien species have generally caused degradation of the services; they have a major impact on the environment, and are threatening biodiversity and reducing overall species abundance and diversity (van Wilgen et al. 2007). On the other hand, some invasive species can provide services useful to human well-being. ...
Globally, invasions by alien plants are rapidly increasing in extent and severity, leading to large-scale ecosystem degradation. One of the most widespread invasive alien plant species in Europe and North America, Tree of Heaven (Ailanthus altissima (Mill.) Swingle) was introduced intentionally for use as an ornamental plant in the 18th century. Since then, it has spread and is now frequently found in a number of countries. Today, Tree of Heaven is considered one of the worst invasive plant species in Europe and is also listed as invasive in North America and many other countries. Millennium Ecosystem Assessment is one of many systems trying to list and categorize biological services to humans and to provide a tool for identifying services delivered by natural ecosystems. Invasive species have generally caused degradation of the services, have a major impact on the environment, and are threatening biodiversity and reducing overall species abundance and diversity. On the other hand, some invasive species can provide services useful to human well-being. In the present review A. altissima impacts on ecosystems are identified and positive influences on some ecosystem services are weighed against the negative effects on the environment and human health. The aim of the present review is to resume the general knowledge of A. altissima, group available references on distribution and ecology according to countries, compare ecosystem services provided or enhanced by A. altissima presence and the negative effects it causes, identify gaps in current knowledge, and give recommendations for future lines of research.
... Giant reed is having significant impacts on the hydrology of South Africa. As the species invades South African riverbanks, it becomes dominant in dense, monotypic stands that replace native vegetation and decrease wildlife diversity (Coffman et al. 2004, van Wilgen et al. 2007). These tall stands of grass have above average water usage (based on per leaf area Giant reed (A. ...
Individually, climate change and invasive species present two of the greatest threats to biodiversity and the provision of valuable ecosystem services. Combined, the complexity of their interactions dramatically increases, and evidence is rapidly growing on how climate change is compounding the already devastating effects of invasive species. Climate change impacts, including warming temperatures and changes in CO2 concentrations, are likely to increase opportunities for invasive alien species because of their adaptability to disturbance and to a broader range of biogeographic conditions. The impacts of those invasive species may be more severe as they increase both in numbers and extent, and as they compete for diminishing resources such as freshwater. Warmer air and water temperatures may also facilitate movement of species along previously inaccessible pathways of spread, both natural and human-made.
Targeted at policy-makers, responsible for developing climate mitigation and adaption strategies that address issues like conservation, ecosystem services, agriculture and sustainable livelihoods, the report focuses on the primary linkages between invasive species and climate change, as well as the secondary and tertiary interactions of their corresponding impacts. Building on a review of existing scientific and conservation literature, the report identifies significant gaps and questions about the intersection of these two major drivers of change. Included case studies highlight key relationships and questions related to invasive species, climate change and the role of ecosystem-based adaptation. Finally, a series of recommendations are intended to provide guidance on the best ways to integrate invasive species prevention and management into the consideration of climate change responses across a range of sectors.
... Invasive alien plants are often ranked as the second most pressing threat (after direct habitat destruction) to global biodiversity. If the infestation of alien plants is not controlled, the threat could increase (van Wilgen et al., 2007). ...
... Nigerians depend on tropical forest ecosystem for both timber and non-timber forest products to meet their daily needs. Forest and biodiversity play important roles in ecosystem services as reported by De Groot et al. (2002), Diaz et al. (2006) and Van Wilgen et al. (2007). These services include water shed management, purification of air, habitat for wild animals, source of medicinal herbs, timber and fuel-wood for rural livelihood and national development. ...
The contributions of a silvicultural practice (enrichment planting technique) to ecosystem restoration, management and biodiversity conservation were assessed. Data were collected from eight 25 × 25 m plots located in the three forest types (Degraded Forest, Strict Nature Reserve and Enrichment Planting Forest) in Akure Forest Reserve, Nigeria, using a systematic line transect. Soil samples were also collected in each plot at three depths. The results indicated that there were 51 tropical hardwood species distributed into 24 families in the forest ecosystem. The Shannon–Weiner indices varied from 3.25 to 2.74. Enrichment Planting Forest was discovered to have the highest number of species, genera and families when compared to the other forest types. Also, highest biodiversity indices were obtained for it. All the variables were significantly higher (p Keywords: enrichment planting; forest reserves; phytosociological; silviculture; soil nutrients Document Type: Research Article DOI: http://dx.doi.org/10.1080/21513732.2013.823464 Affiliations: Department of Forestry and Wood Technology, Federal University of Technology, Akure, Ondo State, Nigeria Publication date: September 1, 2013 $(document).ready(function() { var shortdescription = $(".originaldescription").text().replace(/\\&/g, '&').replace(/\\, '<').replace(/\\>/g, '>').replace(/\\t/g, ' ').replace(/\\n/g, ''); if (shortdescription.length > 350){ shortdescription = "" + shortdescription.substring(0,250) + "... more"; } $(".descriptionitem").prepend(shortdescription); $(".shortdescription a").click(function() { $(".shortdescription").hide(); $(".originaldescription").slideDown(); return false; }); }); Related content In this: publication By this: publisher By this author: Lawal, A. ; Adekunle, V.A. J. GA_googleFillSlot("Horizontal_banner_bottom");
... De acuerdo con Nebel y Porcile (2009) esta especie se ha diseminado a través de los bosques nativos de Uruguay. A la luz de los resultados que demuestran diferencias altamente significativas entre las especies nativas y las introducidas, ya que las primeras se encuentran en promedio casi al doble de distancia de la ciudad de Rivera que las segundas; se sugiere la implementación de programas de manejo de las especies invasoras (Nagler et al., 2005;van Wilgen et al., 2007). Los programas deben focalizarse en los bosques hidrófilos pues ninguna especie exótica se encuentra en los bosques subxerófilos, aspecto que reafirma la influencia humana de las zonas bajas. ...
The northern region of Uruguay undergoes land transformation processes, and degradation of native forest. The existing information on the structure and floristic composition of the forests in that region, as a basis for studies about dynamics, is scarce. Species distribution, floristic composition (wooden species) and forest management, was assessed in the Rivera Region, Uruguay. The study area (33 000 ha) was delimited by 2 simultaneous and complementary approaches, the first one natural (basin) and the other one socioeconomic (reference city). Data from floristic inventories and surveys of producers were captured into a geographic information system. Forests were grouped according to their water gradient associated to contour lines. Native forest area occupies 13.9% of the total study area in Rivera, which means 3 times the national average. Sixty woody species were found, with the Anacardiaceae (26.5%) and Euphorbiaceae (14.7%) as the most frequent families. Anacardiaceae are more common in subxerophytic woods, and Euphorbiaceae in more hydrophilic forests. All forests are vulnerable due to the weak integration between forestry and farming, resulting in no forest management. Non native species constitute a source of degradation of native forests, specifically in areas close to the city.
... Mechanical clearing programmes in the late 20th century were driven by the considerations of poverty relief and available management capacity more than by ecological considerations (van), and no clear targets for assessing progress have been set. While there has been some consideration of the importance of prioritization (van Wilgen et al., 2007; RouraPascual et al., 2009), these approaches have only recently begun to be incorporated into the planning that informs implementation. In this article, we explore the potential for using 'Australian acacias' (species in Acacia subgenus Phyllodineae native to Australia; Miller et al., 2011; Richardson et al., 2011) to develop a framework for the national management of the group as a whole. ...
Aim A range of approaches and philosophies underpin national-level strategies for managing invasive alien plants. This study presents a strategy for the management of taxa that both have value and do harm.
Location South Africa.
Methods Insights were derived from examining Australian Acacia species in South Africa (c. 70 species introduced, mostly > 150 years ago; some have commercial and other values; 14 species are invasive, causing substantial ecological and economic damage). We consider options for combining available tactics and management practices. We defined (1) categories of species based on invaded area (a surrogate for impact) and the value of benefits generated and (2) management regions based on habitat suitability and degree of invasion. For each category and region, we identified strategic goals and proposed the combinations of management practices to move the system in the desired direction.
Results We identified six strategic goals that in combination would apply to eight species categories. We further identified 14 management practices that could be strategically combined to achieve these goals for each category in five discrete regions. When used in appropriate combinations, the prospect of achieving the strategic goal will be maximized. As the outcomes of management cannot be accurately predicted, management must be adaptive, requiring continuous monitoring and assessment, and realignment of goals if necessary.
Main conclusions Invasive Australian Acacia species in South Africa continue to spread and cause undesirable impacts, despite a considerable investment into management. This is because the various practices have historically been uncoordinated in what can be best described as a strategy of hope. Our proposed strategy offers the best possible chance of achieving goals, and it is the first to address invasive alien species that have both positive value and negative impacts.
... Because litters differ in quality and decomposers have preferences for highquality substrates, changes in riparian vegetation composition and diversity can affect aquatic communities (Wood-Eggenschwiler and Bärlocher 1983, Read and Barmuta 1999, Rajashekhar and Kaveriappa 2003, Laitung and Chauvet 2005), and thus, litter-processing rates and ecosystem functioning (Kennedy and Hobbie 2004, Lecerf et al. 2005, 2007a, Riipinen et al. 2009). Forest tree diversity throughout the world has been decreasing via substitution of forests with monocultures of tree species, degradation of riparian corridors by agricultural and industrial activities and urban settlements, and invasion by fast-growing, low-demand alien species (Royer et al. 1999, Graça et al. 2002, Aguiar et al. 2007, van Wilgen et al. 2007). This reduction in plant diversity might be of greatest concern in tropical areas, where the rate of species loss is thought to be the highest (Montagnini and Jordan 2005). ...
Detrital food webs of woodland streams depend on terrestrial litter input and, thus, are susceptible to changes in riparian cover. We assessed effects of litter species richness and quality on decomposition and associated biological communities in temperate deciduous forest and tropical rainforest streams. Three native litter species were incubated in each stream in all combinations (7 litter treatments, 3 richness levels) in coarse- (invertebrate access) and fine-mesh bags (no invertebrate access) and were sampled 5 times over 74 (temperate stream) or 94 d (tropical stream). Decomposition, and fungal biomass, sporulation, and species richness were measured for each treatment. Alnus glutinosa litter was incubated in both streams to assess effects of environmental and biological differences between streams on litter decomposition. Biological colonization (number of fungal species, fungal biomass) and activity (conidial production) were lower in the tropical than the temperate stream, despite its higher water temperature (24 vs 8°C). Mass loss for individual species reached 95% in the temperate and 60% in the rainforest stream. Decomposition rates in mixtures were unaffected by litter richness but could be predicted from their initial N, phenol, and lignin concentrations (leaf quality). In the temperate stream, Alnus decomposition in coarse-mesh bags was positively related to litter richness, and Alnus stimulated decomposition of mixtures. Microbial O2 consumption, fungal biomass accrual, aquatic hyphomycete sporulation rate and richness, and shredder abundance and richness were insensitive to litter richness. In the temperate stream, presence of tough litter inhibited invertebrate colonization of mixtures, whereas in the tropical stream, presence of soft litter stimulated invertebrate colonization of mixtures. Litter quality (species identity), not richness, was the main controller of decomposition of litter mixtures, and decomposition of litter in mixtures may differ from decomposition of individual species. Thus, disappearance or introduction of key species might affect organic matter processing in streams.
... The prioritization presented here was designed to assist with the management of landscape units (typically several hundred hectares in extent). Consequently, factors relevant and operating at other spatial scales (e.g., importance of the area as a watershed for regional water provision, conservation value of the area, adherence to national legislation, prioritization focused on job creation rather than ecological issues) (van Wilgen et al., 2007 ) were excluded from our exercise. Our prioritization should be applied in landscape selected by local-scale planning and therefore does not need to include larger scale factors. ...
Invasive alien trees and shrubs pose significant threats to biodiversity and ecosystem services in South African fynbos ecosystems. An ambitious initiative, the Working for Water program, commenced in 1995 to reduce the extent and impact of plant invasions. Despite substantial progress, the problem remains immense, and innovative ways of improving the efficiency of control operations are urgently needed. This study sought to develop a robust conceptual framework for effective management of the most important invasive alien plant (IAP) species. Two methods were applied in exploring the complexity of problems, thereby identifying appropriate response strategies. The DPSIR (Driving forces-Pressure-State-Impacts-Responses) framework and the Analytic Hierarchy Process (AHP) tool were used to design a strategy for prioritizing management actions. This strategy considers explicitly the most influential factors that determine the distribution, abundance, spread and impacts of IAPs. Efficient management of IAPs is constrained by multiple interacting environmental and socio-economic factors. Factors related to the fire-prone nature of the ecosystem and the characteristics of the invasive stands emerged as pivotal features for setting spatially-explicit priorities for management. Results of the analyses provide an objective and quantifiable perspective for improving the management efficiency. We conclude that considerable progress in controlling the spread of IAPs in fynbos ecosystems could be achieved by better coordination of management practices and by improving the quality of species distribution data.
Biological invasions threaten biodiversity worldwide, especially on tropical Islands such as Reunion Island where the largest area of intact vegetation occurs within the Mascarene’s archipelago. With the impetus of the local government, we initiated a partnership between scientists and managers to address the management of invasive alien plant species on the island. This study aims to map biodiversity priority areas and to prioritise alien plant clearing on the island. We first established a conceptual framework shared by all partners. We then combined all existing data on habitats, both threatened and endemic species, and the distribution of alien plant species using expert knowledge where necessary. We developed a decision-making process using Zonation, a conservation planning tool, to identify biodiversity conservation priorities. Conservation priority areas were selected with the aim of maximising biodiversity levels in areas slightly invaded. The criteria used to identify priority areas for the control of alien plant species included clearing costs, accessibility, and the history of previous management programmes. A total of 60,303 ha were identified as conservation priority areas, 30% of which are not considered to be invaded. Based on biodiversity and implementation issues, we identified plant clearing priority areas that highlighted invasion fronts. Priorities identified helped to spatially re-align existing clearing operations. This study, conducted jointly by managers, decision-makers and scientists has allowed the identification of priority areas concerning the control of alien plants and their implementation thereafter. The engagement of stakeholders at each relevant step of a conservation project is essential in guiding decision making, and the future implementation.
This datasheet on Hakea sericea covers Identity, Overview, Distribution, Dispersal, Hosts/Species Affected, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
Les invasions biologiques menacent la conservation de la biodiversité mondiale, notamment en milieu insulaire comme La Réunion où se trouve les plus grandes reliques de végétation naturelle de l'archipel des Mascareignes. Sous l’impulsion du département de La Réunion, un partenariat a été initié réunissant gestionnaires, décideurs et scientifiques afin de mieux coordonner la lutte contre les espèces végétales envahissantes sur le territoire. Cette thèse, qui s’inscrit dans ce partenariat, a pour objectif principal d’améliorer les connaissances quant à l’état de conservation des milieux naturels afin de prioriser spatialement les actions de lutte contre les plantes exotiques. La thèse comporte trois axes de recherche : 1) la quantification du degré d’invasion à une échelle régionale comme outil d’aide à la décision ; 2) la quantification du degré d’invasion à une échelle locale comme outil d’aide à la gestion ; et 3) la priorisation spatiale des actions de lutte à partir de critères biologiques et opérationnels. Elle se termine sur une réflexion de l’approche transdisciplinaire utilisée à l’interface entre science et gestion. Le degré d’invasion des milieux naturels a été quantifié à deux échelles différentes : régionale (La Réunion) et locale (massifs de Mare Longue et du Volcan). La quantification du degré d’invasion à l’échelle régionale a sollicité en plus des données d’inventaire obtenues grâce au large effort partenarial mis en place ; l’intervention d’experts et le recours à la modélisation. Ainsi les résultats ont montré que 85% de la végétation indigène était envahie dans des proportions différentes, notons que plus de 50% de la végétation reste tout de même peu à pas envahie. A l’échelle locale, un protocole terrain a été mis en place permettant de quantifier le degré d’invasion des trois strates structurantes de l’habitat ; à savoir les strates herbacées, arbustives et arborées. Au travers d’analyses de cluster et de krigeage, une nouvelle cartographie du degré d’invasion à une échelle plus fine (25 x 25 m) a pu être réalisée sur les massifs étudiés. Les résultats ont montré une strate herbacée particulièrement envahie. En parallèle, les enjeux de conservation en termes de biodiversité ainsi que les priorités de gestion des plantes exotiques ont pu être cartographiés à l’échelle de l’ile. Au travers d’une vingtaine d’ateliers de travail avec l’ensemble des partenaires, nous avons pu co-développer une approche partagée par tous. De par l’utilisation de Zonation, un logiciel d’aide à la décision ainsi qu’en respectant les concepts clés de la planification de la conservation, l’approche mise en place a bénéficié des apports de la science. L’inclusion de critères opérationnels, tels que l’accessibilité de la zone ou l’historique des chantiers, a constitué un important apport de la gestion. Ainsi, 60 303 ha ont été identifié comme enjeux de conservation et des priorités de gestion des plantes exotiques à l’échelle de l’île ont pu être définies, mettant en avant la gestion des fronts d’invasion.
Invasive alien species (IAS) induce changes to community structure and functions which lead to a decline of endemic species and major irreversible changes to the local physical habitat. The distribution and the impacts of multiple freshwater IAS are not well known, and they have not been investigated simultaneously at catchment and at European scales.
This study provides an assessment of the distribution and cumulative impact of freshwater IAS over European catchments. IAS occurrences were retrieved from the European Alien Species Information Network geospatial dataset and updated with the most recent records from the literature. The Cumulative Impact Index of Invasive Alien Species (CIMPAL) was derived by aggregating the impacts of species and their occupied area at catchment level by following three steps: i) IAS were scored by both the magnitude of impacts on freshwater ecosystems and the strength of evidence in the literature, ii) scores were mapped over the catchment area, and iii) scores were summed across IAS over the catchment. The distribution of CIMPAL in the river ecological classes of the Water Framework Directive was examined and increasing/decreasing patterns identified across ecological statuses.
Results showed strong spatial variation in the documented distribution and impacts of IAS in Europe. Catchments with CIMPAL scores >40 (range 0–55) clustered in Western European countries (e.g. Belgium and France) were characterised by plant, invertebrate and vertebrate IAS that had both a large impact in magnitude and colonisation at local (catchment level) and large scale (across catchments). CIMPAL showed statistically significant and increasing values from high to bad ecological classes in eight countries only (Belgium, the Czech Republic, Germany, France, Hungary, Italy, Luxemburg, Poland). This study provides comprehensive evidence of the distribution and impact of IAS within freshwater environments that could be used to improve understanding of the ecological pressures at catchment scale.
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 legume Acacia mearnsii invades South Africa’s fynbos riparian zones and may alter the nitrogen (N) dynamics and supply in these areas that typically support few native N fixers. Nitrogen uptake by A. mearnsii may also be influenced by water availability, potentially affecting riparian-specific performance and impact estimations. We expected to find functional differences between the invasive legume and the two co-occurring but non-leguminous native species Brabejum stellatifolium and Metrosideros angustifolia. We also wanted to examine whether in-situ water availability affected N source or uptake in the invasive species. We found A. mearnsii was indeed functioning differently from non-N-fixing native species, and had considerably higher foliar %N. Interestingly, 15N abundance and uptake were associated with site hydrology, meaning water availability should be scrutinised when assuming N-fixing in A. mearnsii using δ15N. Nonetheless, higher water availability to A. mearnsii in fynbos riparian ecosystems did increase foliar N uptake. This has implications for prioritizing clearing of sites with increased nutrient deposition, such as dense stands in relatively moist riparian zones.
Invasive alien plant species are one of the main causes of global biodiversity loss. There are several factors promoting the expansion and establishment of invasive alien plant species. Diverse management actions are being developed in order to stop or decrease the expansion of invasive alien plant species, but due to financial costs the areas for management must be prioritized.
In this study, we propose a prioritization methodology for control actions in areas invaded by an aggressive invasive plant species. An exhaustive bibliographic review about the possible prioritization criteria related to plant species invasion was performed. The most promising criteria were selected and applied in a practical case-study. The methodology was tested using three scenarios based on different weights given to the prioritization criteria: (A) no weighting, (B) giving priority to the success of the control action, and (C) giving priority to the protection of natural values in the landscape mosaics. The methodology was tested in the Baixo Tâmega region (North of Portugal), using as test species an aggressive woody alien invasive species, Acacia dealbata Link. The results showed differences between the scenarios as expected due to the distinct specifications, allowing us to confirm the sensitivity of the method to weighting the several criteria.
The methodology proved to be easy and practical to apply for a rapid establishment of priorities for allocation of control resources. Moreover, it was able to capture different management options, expressed in distinct final priority rankings. Nonetheless, further tests are needed to confirm its effectiveness over a wide range of situations.
Resources for biodiversity conservation and invasive plant management are limited, and restoring invaded vegetation is labour-intensive and expensive. Managers must prioritize their actions to achieve their goals efficiently and effectively. They must distinguish between areas that require only the removal of invasive alien plants (“passive restoration”) from those that require additional restoration measures (“active restoration”). This study used a multi-criterion approach (Analytical Hierarchical Process) to develop a framework for identifying areas that require active restoration, and then to prioritize these areas for active restoration. The South African city of Cape Town is used as a test case to illustrate the utility of the framework. Framework criteria selected in determining the need for active restoration included: dominant alien species invading the area, density of invasion, duration of invasion, indigenous vegetation cover, adjacent land use, level of disturbance, size of the area, aspect, soil texture, soil depth and erodibility, slope and vegetation type. In deciding which areas to prioritize for active restoration, factors such as vegetation conservation status, selection in a regional conservation plan and connectivity function were assessed. Importance in ecosystem functioning (by providing a diversity of habitats and soil conservation) and the delivery of ecosystem service benefits were also considered. The resulting framework provides an objective tool for prioritizing sites for active restoration.
This chapter reviews what is known about those invasive alien species that impact on the terrestrial, freshwater, and marine ecosystems of South Africa. It briefly reviews the pathways by which these species have arrived, how these pathways have changed over time, and how many have become invasive. It then considers the current levels of understanding with respect to impacts, both ecological and economic. This is followed by an account of the prognosis for the growth in these impacts should current trends continue.
The rapid global urban growth poses a great risk to the ecosystem services which are vital to sustaining and fulfilling human life. As an essential part of Fuzhou eco-planning task in south-eastern China, we identified the priority conservation areas for ecosystem services to allow a sustainable urban expansion. We modeled and mapped five ecosystem services (carbon storage, timber production, water yield, water-quality improvement and sediment retention) using InVEST and proposed a definition of priority areas for the conservation of ecosystem services. Priority areas for individual ecosystem services showed that 24% of the region was needed to produce 26% of water yield. Between 6 and 17% of the region was required to conserve at least 20% of other four services, depending on the ecosystem service of interest. In addition, scenarios for multiple ecosystem services conservation were developed using the ordered weighted averaging (OWA) method, a multicriteria evaluation method, to take the tradeoffs among ecosystem services into account. The results showed that, along with the decrease of the OWA risk, the overall areas and the areas at both of the conservative levels dropped gradually. Furthermore, two efficiency indices were created to evaluate the performance of different OWA scenarios. Study results suggested that the efficiency of scenarios was associated with the conservation threshold and OWA risk, as well as the spatial correlation among ecosystem services. In sum, identifying priority areas for ecosystem services in a spatially explicit manner, and analyzing tradeoffs between them, can help make land use and natural resource decisions more effective and efficient.
Managers of invasive species seek to prevent and mitigate their impact, which vary in the time horizon over which they are realized. Likewise, stakeholders vary in the time horizons they consider relevant. Agricultural impacts might reasonably be considered over two or three decades, although ecologists typically consider environmental impacts over much longer time frames. Although time preference plays a critical role in decision making, it has largely been ignored in multicriteria analyses. In this study, we examine how time has been treated in previous decision analyses of invasive species management, focusing on the differences between multicriteria and economic cost–benefit analyses. We then outline a method for incorporating time preference information into multicriteria decision analyses to ensure that criteria weights remain a faithful representation of the decision maker's preferences. To illustrate how time preference can be elicited for invasive species problems involving both monetary and nonmonetary consequences, we describe a small empirical study we conducted with a small group of experts and managers. By outlining a way to consider time preference information in multicriteria analyses of invasive species management, we hope to facilitate better decision making that is reflective of the decision maker's true preferences. Copyright © 2013 John Wiley & Sons, Ltd.
The rapid global urban growth poses a great risk to the ecosystem services which are vital to sustaining and fulfilling human life. As an essential part of Fuzhou eco-planning task in southeastern China, we identified the priority conservation areas for ecosystem services to allow a sustainable urban expansion. We modeled and mapped five ecosystem services (carbon storage, timber production, water yield, water-quality improvement and sediment retention) using InVEST and proposed a definition of priority areas for the conservation of ecosystem services. Priority areas for individual ecosystem services showed that 24% of the region was needed to produce 26% of water yield. Between 6 and 17% of the region was required to conserve at least 20% of other four services , depending on the ecosystem service of interest. In addition, scenarios for multiple ecosystem services conservation were developed using the ordered weighted averaging (OWA) method, a multicriteria evaluation method, to take the trad-eoffs among ecosystem services into account. The results showed that, along with the decrease of the OWA risk, the overall areas and the areas at both of the conservative levels dropped gradually. Furthermore , two efficiency indices were created to evaluate the performance of different OWA scenarios. Study results suggested that the efficiency of scenarios was associated with the conservation threshold and OWA risk, as well as the spatial correlation among ecosystem services. In sum, identifying priority areas for ecosystem services in a spatially explicit manner, and analyzing tradeoffs between them, can help make land use and natural resource decisions more effective and efficient.
Invasive plants pose substantial threats to protected areas globally. Although management can limit impacts, spread and reinvasion from neighbouring areas into protected areas are a major and an on-going problem for land managers. However, identifying the main sources of propagules and the dimensions of invasion pathways is challenging. Th is study used popu-lation genetic markers [inter simple sequence repeats (ISSRs) and amplifi ed fragment length polymorphisms (AFLPs)] to infer the source(s) of re-colonization and dispersal patterns for a typical invader of riparian and terrestrial habitats (Lantana camara) along the Sabie-Sand catchment, one of the most important river systems fl owing into and across South Africa ' s fl agship protected area, the Kruger National Park (KNP). Results indicate that populations located along the lower reaches of the Sabie and Sand tributaries harboured substantially higher genetic diversity than those in the upper Sabie catchment. Bayesian assignments indicated that the upper Sabie tributary contributed far fewer propagules than the Sand tributary to the lower Sabie River. Current invasion patterns are due to a combination of a major fl ood event in 2000 and diff erences in the degree to which the upstream reaches were managed after the fl ooding. Th e major fl ood of 2000 eff ectively cleared lantana from the riparian areas. However, whereas on-going management eff orts against riparian species in the KNP have been eff ective, rendering the upper Sabie relatively clear of lantana, only a small part of the Sand tributary falls under juris-diction of the KNP and has received consistent management attention. Th e reinvasion of the lower Sabie in the KNP was therefore almost entirely by propagules from the Sand tributary. Th e study highlights the important role that molecular tools can play in determining dispersal dynamics and directing invasive species management. For invasive plant species that invade both riparian habitats and landscapes away from rivers in protected areas, such as lantana, management must focus on all major sources of propagules to limit reinvasion. Some invasive alien species cause substantial ecological damage and pose major threats to biodiversity (Gurevitch and Padilla 2004), to the extent that biological invasions are an important driver of global environmental change (Butchart et al. 2010). Protected areas form one of the most important opportunities for conserving biodiversity and ecosystem services globally (Gaston et al. 2008), and invasive species directly threaten the ability of these areas to meet their mandate. Invasive species aff ect ecosystem ser-vices (Vil à et al. 2010), disrupt fi re regimes (D'Antonio and Vitousek 1992, Rossiter-Rachor et al. 2009) and nutrient cycling (Ehrenfeld 2003), and have direct impacts on native species (Vonshak et al. 2010). As key focus areas for conser-vation, protected areas can, and should, be at the forefront of systematic management of invasive species. However, limited resources often result in insuffi cient attention being given to objective prioritization and the integration of all available information to ensure eff ective management. Eradication is feasible for some species, but for most widespread species complete removal is untenable (Rejm á nek
Biological control against incipient, or emerging, weeds (plants in an early stage of invasion) has not been widely practised in many countries, largely because limited budgets tend to be directed at invasions that have already reached detrimental levels. Because of restricted funds and few opportunities for exploration abroad in the past, South African practitioners of biological control have made the most of their survey trips by collecting as many potentially useful control agents, from as many target plants, as they could. Exploration for agents against high-priority weeds thus allowed simultaneous collection of natural enemies of low-priority weeds in the same region. These opportunistic programmes have been beneficial for South Africa in the management of invasive alien plants. In 2003, the Working for Water programme allocated funds for biological control programmes against five emerging weed species. This investment has, for the first time, given formal recognition to the rationale of targeting incipient weeds and bodes well for the future of biological weed control in South Africa. This paper reviews cases where emerging weeds were targeted for biological control in this country, the successes that were achieved, and the prospects for enhancing this approach in the future.
The aquatic plant water hyacinth (Eichhornia crassipes) was first recorded in South Africa during the early part of the 20th century. The plant has since spread across the country and is found in water bodies in both sub-tropical and temperate areas. The biology, ecology and impacts of water hyacinth are well studied, but sound and cost-effective management of it remains an enormous challenge in South Africa. Since the 1970s, control programmes have focused on the use of herbicides, with some success, while biological and integrated control have historically received less effort and investment, despite the successes of the latter control approaches in other parts of Africa and elsewhere in the world. The reasons for the relative successes and challenges associated with the various control approaches vary substantially. Herbicidal control has been an effective short-term solution with highly visible results. However, the cases used in this study show that herbicidal control is approximately five times (R1 481/ha) less costeffective than either biological or integrated control, mainly because it requires resource-intensive follow-up procedures.
The effectiveness of large-scale herbicidal control has mainly been influenced by inappropriate field application, plus management and institutional inconsistencies. Biological control offers a longer term, cheaper (R309/ha and potentially R3.60/ha) and less resource-intensive solution compared to herbicidal treatment, but the effectiveness of this approach relies heavily on the successful release of control agents, the ability of biocontrol agents to thrive under a range of climatic conditions and the extent to which affected water bodies are nutrient-enriched. Based on the analysis here, integrated control was the most cost-effective control option at an average cost of R277/ha. This approach enables managers to integrate selected aspects of herbicidal and biological control and it is also more likely to facilitate the development of partnerships in water hyacinth control programs. Discussion of a possible ‘no control’ option suggests that the economic and environmental costs of no control may be far greater than any control.
Recommendations include: the selection of appropriate management option/s should be based on management needs across different time scales and on objective cost-benefit information—this will help to determine how the costs and benefits of different control approaches could be distributed amongst those who pay for and benefit from the management of water hyacinth. Successful management will also rely on selecting appropriate and sound ecological approaches suited to local conditions; management will also need to facilitate the integration of control efforts at the catchment level as well as institutional and partnership integration to ensure continuity in the ownership of water hyacinth control.
To document the range extension of a plant species in a region in which it was previously absent, we have examined the distribution pattern of Fraxinus ornus L. 65 years after its introduction to the Herault River in southern France. Censuses of flowering individuals showed that Fraxinus ornus successfully colonized, but remained mainly restricted to, flood-disturbed riparian habitats in the Herault River system. The present distribution of this species showed that it spread along the river system at an average rate of 970 m/yr. We suggest that this very rapid spread, of a usually wind-dispersed species, has resulted from water transport of seeds during periodic flooding in autumn.
Effective management of invading alien plants in natural and semi-natural systems is imperative if we are to prevent enormous impacts. An integrated approach involving the combined use of a range of methods is usually necessary to control invasive alien plants effectively. The various methods that are available are usually classified as: mechanical methods (felling, removing of invading alien plants, often in conjunction with burning); chemical methods (using environmentally safe herbicides); and biological control (using species-specific insects and diseases from the alien plant's country of origin). Approaches available for integrated control depend on the species under consideration (features of individual species and the number and identity of species that occur together), features of the invaded systems, the availability of resources and other factors. Mechanical and chemical control are short-term activities, whereas rigorous and disciplined follow-up and rehabilitation are necessary in the medium term. Biological control can provide effective control in the short and medium term in some cases, and it is often the only really sustainable solution in the longer term. We suggest that the biological attributes of plants represent a stable set of attributes, which enable managers to devise control approaches, but that such approaches are likely to be upset by stochastic events such as fires, floods or budget cuts. While an approach of adaptive management, based on trial, error and continual improvement is a logical way in which to progress, the advent of powerful computer simulation modelling technologies will allow managers to do hundreds of 'trial and error' runs in order to explore the consequences of certain courses of action. This should represent an improvement on the current state of affairs, and should allow for better decision-making. We present a series of simulations to illustrate this point.
Predictions that invasive alien plants would use significant amounts of water were a major factor in the establishment of South Africa's Working for Water programme, which aims to protect water resources by clearing these plants. The predictions were made by combining the results of hydrological experiments, conducted to assess the effects of afforestation with alien trees on water resources, with an ecological understanding of the spread and establishment of invasive trees. The forecasts were then scaled up to arrive at national estimates of the corresponding water consumption. This paper reviews the approaches that have been used to estimate these consequences at different scales. We propose a framework for assessing the process of knowledge generation, and review the approaches used in South Africa at each level of the framework, the current level of understanding arising from the use of these methods, and significant gaps in understanding. The framework has four levels: fundamental observations from which a detailed understanding of biophysical processes can be developed; applied or predictive research from which an understanding of processes can be scaled up to predict generic outcomes; integrative research where a predictive understanding of hydrology can be combined with information from other disciplines to place the outcomes in a wider context; and research on management support, such that the information can be used to improve management and policy decisions. We conclude that much knowledge exists, but that there are also significant gaps in understanding, and challenges associated with scaling up and down to make appropriate predictions. This is especially true at the management support level, where very different kinds of uncertainties operate in the same comparative framework. Existing knowledge needs also to be used more effectively, to help prioritize clearing operations by targeting areas in terms of water-related benefits.
Copyright: 2004 Acad Science South Africa This paper reviews relevant available information on rates of total evaporation from black waffle and from grasslands and fynbos shrublands. These data provide an indication of the likely change in catchment water yield following invasion or clearing of black wattle. The assumption is made that over the long term, reductions in total evaporation equate to water yield increases. Soil water storage and leakage from catchments are therefore considered to be small and constant under the different vegetation covers. Author’s review shows that very high rates of total evaporation are possible from dense infestations of black waffle occurring in riparian zones, where there are no soil water deficits through the year. Annual total evaporation from such sites may exceed 1500 mm, a figure that is comparable to many evergreen tropical lowland forests.
Many invasive alien plant species in South Africa are already well-established and cause substantial damage, while scores of others are at the early stages of invasion (only recently introduced and/or entering a phase of rapid population growth). Management programmes must target well-established invaders, but must also give appropriate attention to emerging problems. Protocols for objectively prioritizing species in the two groups for management action are lacking. To this end, the authors describe the objective derivation of two lists of invasive alien plants in South Africa, using available quantitative data and expert knowledge on current patterns of distribution and abundance, life-history traits, and (for emerging invaders) estimates of potential habitat. 'Major invaders' are those invasive alien species that are well-established, and which already have a substantial impact on natural and semi-natural ecosystems. 'Emerging invaders' currently have less influence, but have attributes and potentially suitable habitat that could result in increased range and consequences in the next few decades. We describe the derivation of lists that contain 117 major invaders (categorized into groups based on geographical range and abundance) and 84 emerging invaders (categorized into groups based on current propagule-pool size and potentially invasible habitat). The main lists, and groupings within them, provide a useful means for prioritizing species for a range of management interventions at national, regional and local scales.
Invasive alien plants are consumptive water-users, and may have reduced river flows in South Africa by about 6.7% according to a broad-scale study. An effective programme to bring the invasions under control would cost about US$ 92 million per year for the next 20 years. This paper reports on studies of four representative catchments (The Sonderend, Keurbooms, Upper-Wilge and Sabie-Sand) to assess the impacts and costs of invasions at a scale that is more relevant to managers. Several alien plant species have invaded the catchments. Non-riverine invasions are mainly Pinus and Hakea species in Sonderend and Keurbooms, eucalypts in the Upper Wilge, and pines and scramblers (e.g. Lantana camara) in the Sabie-Sand catchment. Riverine invasions are dominated by Acacia mearnsii and, to a lesser extent, A. dealbata, except in the Sabie-Sand and the lower Sonderend River where Eucalyptus species are important. The impacts and costs are significant and are comparable with those calculated independently for other South African catchments. Water is acknowledged to be a key constraint to economic growth in South Africa and there is considerable pressure for efficient and sustainable use of the limited water resources. The projected impacts would justify control programmes aimed at clearing alien invader, for water conservation.
This article explores the strategies that were, and are being, used to facilitate the transition from scientific development to operational application of the South African River Health Programme (RHP). Theoretical models from the field of the management of technology are used to provide insight into the dynamics that influence the relationship between the creation and application of environmental programmes, and the RHP in particular. Four key components of the RHP design are analysed, namely the (a) guiding team, (b) concepts, tools and methods, (c) infra-structural innovations and (d) communication. These key components evolved over three broad life stages of the programme, which are called the design, growth and anchoring stages.
The first biological control project against invasive alien plants in South Africa was in 1913. Initially, invasive cactus species were the only plants in South Africa targeted for biological control. By the early 1960s, the emphasis expanded to include problem plants that threatened the 'Fynbos' biome, and latterly to invasive species in other types of natural habitats. Many of the South African projects have been innovative, for example: the use of gall-forming and seed-feeding insect species that have not been used elsewhere; the emphasis on weeds in conservation areas; and the predominance of woody invaders that have been targeted for biological control. Most of these woody plants originated as forestry or agro-forestry introductions, which has created a relatively high incidence of conflicts of interest between conservationists and growers. Recent benefit:cost analyses have demonstrated exceptionally high returns on investment for biological control, even for the least successful of the projects. The inception of the Working for Water programme in 1995 has significantly enhanced biological weed control in South Africa. The benefits include: sustainable funding; investment in research on emerging weeds; a well-organized implementation programme that has increased the impact of biological control in the field; improved international cooperation, particularly in Africa, in concert with the NEPAD initiative; and the recent re-organization of research personnel into cooperative teams that include entomologists, plant pathologists, resource economists and plant ecologists.
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.
Invasibility of riparian plant communities was estimated by the percentage of alien species found along the Adour River (Southwest France) and along Lockout Creek, McKenzie River, and Willamette River (Central Cascades, Oregon, U.S.A.). At the patch scale, the invasibilities of riparian plant communities were compared between one exceptionally rich site of the Adour River and patches selected in the Hoh and Dungeness watersheds (Olympic Peninsula, Washington, U.S.A.). Alien species represented 24% of 1396 species for the Adour and 30% of 851 species for the McKenzie. They represented 24% of 148 species for the Hoh drainage and 28% of 200 species for the Dungeness drainage. Similar trends were found along the Adour River and along the McKenzie River for changes in total number of species per site and in percentages of alien species per site. These trends may be related to the intermediate disturbance regimes and to the physical structure of the riparian corridors. Climatic and human factors are also involved in these longitudinal changes. Positive linear relationships were found between the total number of species and the percentage of aliens observed in each site. At the patch scale, most of the sampled communities contained alien species. Although mature vegetative patches appeared to be invasible, young communities contained more alien species than older ones. For entire corridors, a positive linear relationship was found between total species richness and percentage of alien species in each patch type for the richest site of the Adour River. This may be partially explained by landscape features considered in a successional context. We suggest the use of empirical rules, and stress the importance of riparian systems for monitoring the conservation of local and regional species pools are suggested.
1. Historically, biogeographic barriers to the movement of aquatic organisms existed at multiple spatial scales and contributed to the development of unique regional faunas. At increasing spatial scales, these barriers consisted of waterfalls and cascades; catchment divides; major mountain ranges and oceans. This hierarchy of movement barriers produced increasingly distinct aquatic biotas at larger drainage units.
2. Humans have provided a variety of pathways by which aquatic species can circumvent historical biogeographic barriers. These include both authorised and unauthorised stocking, construction of canals and water conveyance systems, transport in ship ballast water, fishing and angling gear (including boats) transferred among water bodies and intentional release of ornamental and other captive species.
3. One consequence of human-aided breaching of biogeographic barriers has been the spread of noxious species that have altered aquatic ecosystems and fisheries in ways that are undesirable to humans.
4. Another consequence of human-aided breaching of biogeographic barriers has been the homogenization of aquatic biotas. Homogenization occurs when a few cosmopolitan species come to dominate communities at the expense of unique native species. Among aquatic organisms this phenomenon is best documented for fish faunas where a small set of species introduced for sport fishing, aquaculture, or ornamental purposes have become widespread throughout the world.
5. Slowing biotic homogenization will require slowing the rate at which species breach biogeographic barriers. This will involve implementing regulations that limit stocking opportunities; increasing the public's awareness about the consequences of releasing non-native species and developing technological solutions that prevent movement of aquatic organisms or eliminate them before they become established.
6. River restoration can influence homogenization of aquatic biotas through two major mechanisms: by removing barriers to movement and by restoring natural habitat conditions. Removal of movement barriers may facilitate the spread of non-native species and thus contribute to biotic homogenization. Restoration of natural flow regimes and habitat conditions may reduce biotic homogenization by favouring regional native species over cosmopolitan, non-native species.
The concept of process domains is proposed as an alternative to the River Continuum Concept for the influence of geomorphic processes on aquatic ecosystems. Broadly defined, the Process Domain Concept is a multi-scale hypothesis that spatial variability in geomorphic processes governs temporal patterns of disturbances that influence ecosystem structure and dynamics. At a coarse scale, regional climate, geolog vegetation, and topography control the suite of geomorphic processes that are distributed over a landscape. Within the broad context so defined, stream channel classification can guide identification of functionally similar portions of a channel network, but the response of otherwise similar reaches can depend upon their geologic and geomorphic context. Within geomorphic provinces defined by differences in topography, climate history, and tectonic setting, areas with generally similar geology and topography define lithotopo units, which are useful for stratifying different suites of dominant geomorphic processes. Process domains are spatially identifiable areas characterized by distinct suites of geomorphic processes, and the Process Domain Concept implies that channel networks can be divided into discrete regions in which community structure and dynamics respond to distinctly different disturbance regimes. The concepts of process domains and lithotopo units provide both a framework for the application of patch dynamics concepts to complex landscapes and a context for addressing the effects of watershed processes on the ecology of mountain drainage basins.
1. Despite wide recognition of the need for catchment-scale management to ensure the integrity of river ecosystems, the science and policy basis for joint management of land and water remains poorly understood. An interdisciplinary case study of a river basin in south-eastern Michigan is presented.
2. The River Raisin drains an area of 2776 km2, of which some 70% is agricultural land. The upper basin consists of till and outwash, and both topography and land use/cover are diverse. The lower basin consists of fine textured lake deposits, is of low relief, and land use is primarily agricultural.
3. The River Raisin basin historically was a region of oak-savannah and wetlands. It was deforested, drained and converted to farmland during the mid-nineteenth century. Human population reached a plateau at about 1880, and then underwent a second period of growth after 1950, mainly in small urban areas. More recently, the amount of agricultural land has declined and forested land has increased, in accord with a general decline in farming activity.
4. It could be suggested that the influence of land use on stream integrity is scale-dependent. Instream habitat structure and organic matter inputs are determined primarily by local conditions such as vegetative cover at a site, whereas nutrient supply, sediment delivery, hydrology and channel characteristics are influenced by regional conditions, including landscape features and land use/cover at some distance upstream and lateral to stream sites.
5. Sediment concentrations measured during low flows were higher in areas of greater agriculture. In a comparison of two subcatchments, sediment yields were up to ten times greater in the more agricultural location, in response to similar storm events. A distributed parameter model linked to a geographical information system predicted that an increase in forested land cover would result in dramatic declines in runoff and sediment and nutrient yields.
6. Habitat quality and biotic integrity varied widely among individual stream sites in accord with patterns in land use/cover. Extent of agricultural land at the subcatchment scale was the best single predictor of local stream conditions. Local riparian vegetation was uncorrelated with overall land use and was a weak secondary predictor of habitat quality and biotic integrity.
7. Investigation of the regulatory agencies involved in land and water management in the basin revealed a complex web of overlapping political jurisdictions. Most land-use decision-making occurs at the local level of township, city or village. Unfortunately, local decision-making bodies typically lack the information and jurisdictional authority to influence up- and downstream events.
This paper describes the history of conservation in the Cape Floristic Region, and the development of a conservation action plan for the region, arising from the Cape Action Plan for the Environment (CAPE). The plan turns the long-term strategy, which identified priorities for conservation action, into a practical 5-year action plan. The tension between protection and the use of natural resources is addressed within the context of institutional frameworks. CAPE has succeeded in bringing together previously fragmented institutions, and has ensured that they work together more effectively. It has also strategically realigned existing resources earmarked for conservation. The factors that contributed to this success include a long history of research-based management; the existence of a body of understanding and knowledge that made it possible to rapidly assess conservation priorities; a small but viable number of scientists to carry out the planning phase of the project and institutions willing to take it forward.
Copyright: 2004 Blackwell Publishing Ltd Most national or regional initiatives aimed at managing biological invasions lack objective protocols for prioritizing invasive species and areas based on likely future dimensions of spread. South Africa has one of the most ambitious national programmes for managing plant invasions in the world. There is, however, no protocol for assessing the likely future spread patterns needed to inform medium- to long-term planning. This paper presents an assessment of the climatic correlates of distribution of 71 important invasive alien plants, and an analysis of the implications of these findings for future invasions in different vegetation types in South Africa, Lesotho and Swaziland over the next few decades. We used a variant of climatic envelope models (CEMs) based on the Mahalanobis distance to derive climatic suitability surfaces for each species. CEMs were developed using the first three principal components derived from an analysis of seven climatic variables. Most species are currently confined to 10% or less of the region, but could potentially invade up to 40%. Depending on the species, between 2% and 79% of the region is climatically suitable for species to invade, and some areas were suitable for up to 45 plant invaders. Over one third of the modelled species have limited potential to substantially expand their distribution. About 20% of the vegetation types have low invasion potential where fewer than five species can invade, and about 10% have high invasion potential, being potentially suitable for more than 25 of the plant invaders. Author’s results suggest that management of the invasive plant species that are currently most widespread should focus on reducing densities, for example through biological control programmes, rather than controlling range expansions. The authors also identify areas of the region that may require additional management focus in the future.
Copyright: Elsevier Science Ltd In this paper, South Africa’s working for water programme is described. The programme maximizes an ecosystem services (the delivery of water), enhances sustainability by eliminating invading alien plants, and promotes social equity through jobs and training for economically marginalized people. It demonstrates the potential value of placing a monetary estimate on an ecosystem service.
The Working for Water programme is a pioneering environmental conservation initiative in that its implementation successfully combines ecological concerns and social development benefits. By addressing unemployment, skills training and empowerment, the HIV/AIDS pandemic, and transformation issues, the programme gained political support and secured significant funding. Developing a range of social interventions brought significant challenges, however, with little opportunity as yet for a comprehensive research programme. This paper presents the ways in which the programme has contributed to poverty alleviation and social upliftment while controlling invasive alien plants, and outlines plans for three research projects.
Fish faunas across the continental United States have become more similar through time because of widespread introductions
of a group of cosmopolitan species intended to enhance food and sport fisheries. On average, pairs of states have 15.4 more
species in common now than before European settlement of North America. The 89 pairs of states that formerly had no species
in common now share an average of 25.2 species. Introductions have played a larger role than extirpations in homogenizing
fish faunas. Western and New England states have received the most introductions, which is a reflection of the small number
of native fishes in these areas considered desirable gamefish by settlers.
Freshwater biodiversity is the over-riding conservation priority during the International Decade for Action - 'Water for Life' - 2005 to 2015. Fresh water makes up only 0.01% of the World's water and approximately 0.8% of the Earth's surface, yet this tiny fraction of global water supports at least 100000 species out of approximately 1.8 million - almost 6% of all described species. Inland waters and freshwater biodiversity constitute a valuable natural resource, in economic, cultural, aesthetic, scientific and educational terms. Their conservation and management are critical to the interests of all humans, nations and governments. Yet this precious heritage is in crisis. Fresh waters are experiencing declines in biodiversity far greater than those in the most affected terrestrial ecosystems, and if trends in human demands for water remain unaltered and species losses continue at current rates, the opportunity to conserve much of the remaining biodiversity in fresh water will vanish before the 'Water for Life' decade ends in 2015. Why is this so, and what is being done about it? This article explores the special features of freshwater habitats and the biodiversity they support that makes them especially vulnerable to human activities. We document threats to global freshwater biodiversity under five headings: overexploitation; water pollution; flow modification; destruction or degradation of habitat; and invasion by exotic species. Their combined and interacting influences have resulted in population declines and range reduction of freshwater biodiversity worldwide. Conservation of biodiversity is complicated by the landscape position of rivers and wetlands as 'receivers' of land-use effluents, and the problems posed by endemism and thus non-substitutability. In addition, in many parts of the world, fresh water is subject to severe competition among multiple human stakeholders. Protection of freshwater biodiversity is perhaps the ultimate conservation challenge because it is influenced by the upstream drainage network, the surrounding land, the riparian zone, and - in the case of migrating aquatic fauna - downstream reaches. Such prerequisites are hardly ever met. Immediate action is needed where opportunities exist to set aside intact lake and river ecosystems within large protected areas. For most of the global land surface, trade-offs between conservation of freshwater biodiversity and human use of ecosystem goods and services are necessary. We advocate continuing attempts to check species loss but, in many situations, urge adoption of a compromise position of management for biodiversity conservation, ecosystem functioning and resilience, and human livelihoods in order to provide a viable long-term basis for freshwater conservation. Recognition of this need will require adoption of a new paradigm for biodiversity protection and freshwater ecosystem management - one that has been appropriately termed 'reconciliation ecology'.
Towards harmony with the land: the drainage basin ecosystem context. Environmental Planning and Management
- K L Tinley
Tinley K.L. (1991) Towards harmony with the land: the
drainage basin ecosystem context. Environmental Planning and Management, 2, 3-5.
Environmental Flow Assessments for Rivers: Manual for the Building Block Methodology
- J M King
- R E Tharme
- M S De Villiers
King J.M., Tharme R.E. & de Villiers M.S. (2000) Environmental Flow Assessments for Rivers: Manual for
the Building Block Methodology. Report no. TT 131/
00, Water Research Commission, Pretoria.
River heterogeneity: ecosystem structure, function and management
- K H Rogers
- J O'keefe
Rogers K.H. & O'Keefe J. (2003) River heterogeneity:
ecosystem structure, function and management. In: The
Kruger Experience: Ecology and Management of Savanna
Heterogeneity (Eds J.T. Du Toit, K.H. Rogers & H.C.
Biggs), pp. 189-218. Island Press, Washington D.C.
Department of Water Affairs and Forestry, Cape Town. Department of Water Affairs and Forestry (2002) National Water Resource Strategy, 1st edn. Department of Water Affairs and Forestry
- Anonymous
Anonymous (2003) The Working for Water Programme
Annual Report 2002/03. Department of Water Affairs
and Forestry, Cape Town.
Department of Water Affairs and Forestry (2002) National
Water Resource Strategy, 1st edn. Department of Water
Affairs and Forestry, Pretoria. URL: http://www.
dwaf.gov.za/Documents/Policies/NWRS/Default.htm
(accessed 14 February 2007).
- A Driver
- K Maze
- M Rouget
Driver A., Maze K., Rouget M. et al. (2005) National
Spatial Biodiversity Assessment 2004: Priorities for
Biodiversity Conservation in South Africa. Strelitzia
17, South African National Biodiversity Institute,
Pretoria.
Freshwater biodiversity: importance, threats, status and conservation challenges
- D Dudgeon
- A H Arthington
- M O Gesser
Dudgeon D., Arthington A.H., Gesser M.O. et al. (2006)
Freshwater biodiversity: importance, threats, status
and conservation challenges. Biological Reviews, 81,
163-182.
Invasive Species in a Changing World
- H A Mooney
- R J Hobbs
Mooney H.A. & Hobbs R.J. (2000) Invasive Species in a
Changing World. Island Press, Washington D.C.
Towards harmony with the land: the drainage basin ecosystem context
- Tinley K.L.