Browsing by Author "Zimmermann, H G"

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    A proposed prioritization system for the management of invasive alien plants in South Africa
    (2003) Robertson, M P; Villet, M H; Fairbanks, D H K; Henderson, L; Higgins, S I; Hoffmann, J H; Le Maitre, D C; Palmer, A R; Riggs, I; Shackleton, C M; Zimmermann, H G
    Every country has weed species whose presence conflicts in some way with human management objectives and needs. Resources for research and control are limited, so priority should be given to species that are the biggest problem. The prioritization system described in this article was designed to assess objectively research and control priorities of invasive alien plants at a national scale in South Africa. The evaluation consists of seventeen criteria, grouped into five modules, that assess invasiveness, spatial characteristics, potential impact, potential for control, and conflicts of interest for each plant species under consideration. Total prioritization scores, calculated from criterion and module scores, were used to assess a species' priority. Prioritization scores were calculated by combining independent assessments provided by several experts, thus increasing the reliability of the rankings. The total confidence score, a separate index, indicates the reliability and availability of data used to make an assessment. Candidate species for evaluation were identified and assessed by several experts using the prioritization system. The final ranking was made by combining two separate indices, the total prioritization score and the total confidence score. This approach integrates the plant's perceived priority with an index of data reliability. Of the 61 species assessed, those with the highest ranks (Lantana camara, Chromolaena odorata and Opuntia ficus-indica) had high prioritization and high confidence scores, and are thus of most concern. Those species with the lowest ranks, for example, Harrisia martinii, Opuntia spinulifera and Opuntia exaltata, had low prioritization scores and high confidence scores, and thus are of least concern. Our approach to ranking weeds offers several advantages over existing systems because it is designed for multiple assessors based on the Delphi decision-making technique, the criteria contribute equally to the total score, and the system can accommodate incomplete data on a species. Although the choice of criteria may be criticized and the system has certain limitations, it appears to have delivered credible results.
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    Biological control in the management of invasive alien plants in South Africa, and the role of the Working for Water programme
    (2004) Zimmermann, H G; Moran, V C; Hoffmann, J H
    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.