Browsing by Author "van Wilgen, B W"

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    A proposed classification of invasive alien plant species in South Africa: Towards prioritising species and areas for management action
    (2004) Nel, J L; Richardson, D M; Rouget, M; Mgidi, T N; Mdzeke, N; Le Maitre, D C; van Wilgen, B W; Schonegevel, L; Henderson, L; Neser, S
    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, we 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
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    A rapid assessment of the invasive status of Eucalyptus species in two South African provinces
    (2004) Forsyth, G G; Richardson, D M; Brown, P J; van Wilgen, B W
    Gum trees, or eucalypts (Eucalyptus species), have been targeted for invasive alien plant clearing programmes in many parts of South Africa. This has caused some dissatisfaction where the species concerned also have useful characteristics, and stakeholders contend that some of these useful species are not invasive. A rapid assessment of the invasive status of Eucalyptus species at 82 sites in South Africa (54 in the Western Cape and 28 in Mpumalanga) indicated that only Red River gum (E. camaldulensis) and flooded gum (E. grandis) are clearly invasive. Surveys were not undertaken in parts of the Western Cape known to be invaded by spider gum (E. lehmannii); the invasive status of this species is well known and is not contested. Red River gum has transformed long stretches of rivers and its importance as a major weed has been underestimated in previous reviews of alien plant invasions in South Africa. Most other species were naturalized. We recommend that projects aimed at clearing eucalypts should focus on riparian areas and nature reserves (where all eucalypts have deleterious effects), but that clearing projects outside these areas should only target species known to be invasive until such time as the invasive status of the other eucalypts (notably sugar gum, E. cladocalyx, and karri, E. diversicolor) can be ascertained with a greater degree of confidence.
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    A status quo, vulnerability and adaptation assessment of the physical and socio-economic effects of climate change in the Western Cape
    (2005) Midgley, G F; Chapman, R A; Hewitson, B; Johnston, P; de Wit, M; Ziervogel, G; Mukheibir, P; van Niekerk, L; Tadross, M; van Wilgen, B W; Kgope, B; Morant, P D; Theron, A; Scholes, R J; Forsyth, G G
    The South African Country Study on Climate Change, carried out in the late 1990’s, identified the Northern and Western Cape Provinces as being most at risk from projected climate change-induced warming and rainfall change (results of this study are summarized in South Africa’s initial National Communication, prepared in accordance with Article 12 of the United Nations Framework Convention on Climate Change: www.environment.gov.za/Documents/Documents/2005Feb22/NatCom_Nov%202003%20(b). doc ). However, this study was based on a limited set of model projections of climate change that have now been superseded by projections using more advanced techniques. In this study we have carried out a broad reassessment of the vulnerability of the Western Cape to climate change impacts, using a wider range of climate scenarios from more sophisticated climate models, and for a range of sectors (with the exception of agriculture and fisheries, according to our brief). We also identify some key adaptive strategies that might alleviate or avoid the worst impacts of climate change in some sectors. We conclude that further detailed study of some of the implications of these findings will be necessary to explore these and further strategies in order to guide policy development.