Browsing by Author "Rouget, Mathieu"
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- ItemOpen AccessAlien plant invasion on the Agulhas Plain : a detailed description of invasion patterns(2004) Blanchard, Ryan; Richardson, David Mark; Rouget, MathieuInvasive alien species occur within several biodiverse regions of South Africa. It is not yet fully understood the extent to which invasive alien species affect natural vegetation. It is important to classify such species based on abundance and distribution in order to determine invasion patterns and set priorities for management within a region. Such a study was adapted for the Agulhas Plain of South Africa in the Cape Floristic Region. Eucalyptus lehmannii was recognised as the top invasive alien species, occupying both natural and transformed landscapes at high densities, >130% canopy cover. Acacia saligna and Acacia cyclops are the most widely distributed species, covering 41 % and 53% of the total area. Effectively determining invasive alien species richness required the use different variables to those used in this study. Invasive alien species invasion pattern was classified into two groups, namely coastal invasion and interior invasion. These characteristics differed with regards to vegetation types and species composition. Natural vegetation within the Mountain fynbos (100% invaded), Dune fynbos (91 % invaded) and Mountain top fynbos (99% invaded) vegetation types were largely threatened by invasive alien species. Vegetation types largely affected by transformation include Elim asteraceous fynbos (89% transformed) and Renoster fynbos. The invasion patterns described could be used in prioritisation of manageable land.
- ItemRestrictedCurrent patterns of habitat transformation and future threats to biodiversity in terrestrial ecosystems of the Cape Floristic Region, South Africa(2003) Rouget, Mathieu; Richardson, David M; Cowling, Richard M; Lloyd, J Wendy; Lombard, Amanda TThe formulation of an effective strategic plan for biodiversity conservation in the Cape Floristic Region (CFR) requires an assessment of the current situation with regard to habitat transformation, and an explicit framework for predicting the likelihood of remaining habitat (i.e. that potentially available for conservation) being transformed. This paper presents the results of a detailed assessment of the current and future extent of three important factors that threaten biodiversity in the CFR: cultivation for intensive agriculture (including commercial forestry plantations), urbanisation, and stands of invasive (self-sown) alien trees and shrubs. The extent of habitat transformation was mapped at the scale of 1:250,000, using primarily satellite imagery. We compared models derived from a rule-based approach relying on expert knowledge and a regression-tree technique to identify other areas likely to be affected by these factors in future. Cultivation for agriculture has transformed 25.9% of the CFR and dense stands of woody alien plants and urban areas each cover 1.6%. Both models predict that at least 30% of the currently remaining natural vegetation could be transformed within 20 years. There was an overall accuracy of 73% between both models although significant differences were found for some habitat types. Spatial predictions of future agriculture threats derived from the rule-based approach were overestimated relative to the statistical approach, whereas future alien spread was underestimated. Threat assessment was used to derive conservation targets for subsequent stages of conservation planning for the CFR. The importance of integrating vulnerability knowledge into conservation planning is discussed. The choice of vulnerability analysis (future habitat degradation and/or impact on biological entities) and methods will depend on the complexity of the threatening processes and the availability of spatial data.
- ItemOpen AccessAn integrated planning approach for the conservation of freshwater ecosystems in South Africa(2009) Amis, Mao Angua.; Day, Jenny; Rouget, MathieuFreshwater ecosystems underpin the fabric of society and the environment, providing essential ecosystem services such as water and food, upon which all human beings depend. In order to secure these vital services requires the sustainable management of freshwater ecosystems. At present however, freshwater biodiversity is under severe threat from anthropogenic disturbances, and the situation is expected to worsen due to population growth and global change. Coupled with the threats to freshwater biota are the limited resources available to secure their protection. There is a need to therefore prioritise freshwater ecosystems in a comprehensive, adequate and representative manner to maximise the outcomes of conservation effort. The concept of systematic conservation planning was developed to address this challenge. It offers a suitable framework for achieving conservation goals in the face of other competing land uses. The principles of systematic conservation planning are being widely applied in terrestrial and marine ecosystems, but their application in freshwater ecosystems is still relatively limited. Freshwater ecosystems provide challenges to conservation planning that are unique from those of terrestrial and marine ecosystems, such as the longitudinal nature of river systems and the associated connectivity, and catchment divides that constrain some obligate species. As a result freshwater ecosystems require conservation planning tools and approaches that are specifically geared towards addressing these unique challenges. Progress has recently been achieved in addressing some of these challenges, but there are still other outstanding issues that have not been comprehensively addressed. The aim of this thesis was to develop new frameworks, and test approaches for the application of systematic conservation planning principles in the conservation of freshwater ecosystems in South Africa. The thesis addressed a range of issues along the systematic conservation planning continuum from biodiversity assessment to implementation. I first carried out a focused review of systematic conservation literature between 1987- 2006, to gauge the extent to which freshwater ecosystems have being integrated in conservation assessments. Most of the focus was found to be on terrestrial ecosystems with minimal incorporation of freshwater biodiversity. Wetlands for example, were in most cases incorporated into conservation assessments without taking their diversity into account. This was partly attributed to the difficulty of classifying wetlands. I therefore developed and tested a hierarchical GIS framework for automating wetland classification as a strategy for incorporating wetland biodiversity, functions and benefits into broad scale conservation planning.
- ItemRestrictedIntegrating freshwater and terrestrial priorities in conservation planning(2009) Amis, Mao A; Rouget, Mathieu; Lotter, Mervyn; Day, JennyThe integration of freshwater and terrestrial biodiversity priorities in systematic conservation planning is a major challenge to conservation planners. Maintaining upstream–downstream connectivity and the influence of catchments on freshwater ecological integrity are some of the issues that make it difficult to reconcile terrestrial and freshwater conservation planning. As a result most conservation assessments are often biased towards terrestrial systems without adequate incorporation of freshwater biodiversity in determining priority areas for conservation. In this paper, we propose a protocol for integrating the assessment of freshwater and terrestrial priorities in conservation planning, based on a case study from Mpumalanga Province in South Africa. The approach involves the separate assessment of freshwater priority areas, and using the outcome to influence the selection of terrestrial priority areas. This allowed both freshwater and terrestrial biodiversity to be incorporated in conservation planning without compromising their unique requirements. To test the effectiveness of this approach, we assessed percentage overlap between freshwater and terrestrial priority areas, target achievement, and the area required to achieve targets. We then compared the outcome from the proposed approach with the separate assessments of freshwater and terrestrial biodiversity priorities, and when both systems are given an equal weighting in a single assessment. The results showed that there was a noticeable improvement in the overlap of priority areas for freshwater and terrestrial biodiversity from 23% to 47%. Target achievement for freshwater biodiversity improved by 10% when terrestrial assessment was based on freshwater priority areas as opposed to terrestrial systems being assessed alone. There was negligible increase in area required, whether there was integration of freshwater and terrestrial biodiversity or no integration. We conclude that the most efficient way to achieve integration in conservation planning is to preferentially select areas where freshwater and terrestrial biodiversity priorities overlap.
- ItemOpen AccessModelling the current and potential distribution of woody plants, with special emphasis on the importance of spatial scale and environmental factors(2002) Rouget, Mathieu; Richardson, Dave; Cowling, Richard M; Lavorel, Sandra; Milton, Suzanne JaneThe relationship between species distribution and environment has always been a central issue in ecology. The primary aim of this thesis is to explore the role of abiotic and biotic factors in mediating the distribution of woody plants, particularly invasive alien species. Predictions of the future distribution of invasive species are required for management, conservation actions, and legislation. Using predictive geographical modelling, this thesis assesses the role of spatial scale in understanding the determinants of species distribution, modelling invasion spread, and taking conservation decisions. The species distribution databases were collated in a Geographic Information System from various sources (from field mapping to remote-sensing data), and at various spatial scales (from local to sub-continental). Classification and regression trees, a flexible non-parametric statistical technique, were developed for each case study. I show that static modelling approaches, such as classification trees, are appropriate for modelling species distribution at regional to sub-continental scales. More mechanistic approaches, which include biological attributes, are required for accurate modelling of species abundance at local scale. A hierarchy of environmental factors was observed. Abiotic factors such as climate were more important for modelling species distribution at broad scales, whereas biotic factors were the fine-scale drivers of species distribution and abundance. This highlights the scale- dependence of prediction accuracy and of environmental drivers. Predictive habitat modelling was also applied to modelling future land use changes (including invasive alien species) in the context of conservation planning for the Cape Floristic Region. Effective conservation planning requires a detailed assessment of current land use patterns and future land use scenarios. Conservation planning is generally derived at regional scale but implementation takes place at finer scales. I investigated the transition from broad-scale planning to fine-scale implementation. This work emphasises the importance of diverse and fragmented habitats in measuring conservation value. This thesis concludes by linking predictive habitat modelling, species determinants, and application types to the spatial scale analysed.
- ItemOpen AccessPattern and process of plant invasion in an African savanna ecosystem, with emphasis on multiple spatial and temporal scales(2007) Foxcroft, Llewellyn Courtney; Richardson, David Mark; Rouget, MathieuBiological invasions are a significant ecological and economic global crisis. Protected areas also suffer from the increased burden that invasions place on their resources and the impacts placed on the ecosystem. However, management requires an ecological foundation which can inform best practice and optimize its responses. l explored the patterns and processes of invasion in Kruger National Park (KNP), South Africa; a large national park situated in the Lowveld savanna ecosystem. l used spatially-explicit alien plant data at various scales from a national database, the whole of KNP, a specific region, river system, and small scale plots in one invaded area of KNP. Using various statistical techniques, primarily classification and regression tree analysis, logistic regression, ANOVA, Nestedness and spatial pattern analysis, I assessed the relationship between the patterns observed at a specific spatial grain and extent, discussing the implications for invasion ecology and management. Using this knowledge and conceptual tools, I developed a new framework and model which contributes to invasion theory. Scale is a critical component in evaluating alien plant invasions. Without careful consideration of scale, studies from different scenarios cannot be compared and the science of invasion ecology will not advance. I provide a framework for assessing the risks of plant invasions in a watershed, using both an area- and species-approach, highlighting areas of current and future potential concern. I also explore the role of intentional introduction of ornamental plants and discuss management approaches for dealing with this. Evaluating a riparian system provides insights into how different patches in a landscape are differentially invaded, and how patch type characteristics need to be considered carefully for management and monitoring. I also describe how reconstructing the invasion history of a species, complemented by fine scale assessment, provides insights into species-specific spread models, and also how these types of studies can input into general theories, such as the role of propagule pressure. These components together provide insight into the dynamics of alien plant invasions in an African savanna and protected area system.