Current degree level: MSc
Field of specialisation: Biological invasions
Project title: Determining the invasive potential of Crotalariaagatiflora in South Africa
Promoter: Prof. Ben-Erik Van Wyk
Co-promoter: Dr Stephen James Boatwright
Hons: The morphology, anatomy, essential oil chemistry and Antimicrobial activity of Trachyspermum ammi (Ajowan)
Crotalaria agatiflora is native to tropical East Africa (Tanzania, Ruanda, Burundi, Kenya and Ethiopia). In South Africa this plant was introduced as an ornamental garden shrub, and has since become invasive in many localities (savanna, grasslands, watercourses and forest margins). It is found along road verges, riparian areas, dump sites and abandoned sites in Limpopo, Gauteng, Mpumalanga, Kwa-Zulu Natal and one population in both the Eastern and Western Cape. This project aimed to see whether it poses a significant threat to the biodiversity and ecosystems of the country, so that we are able to provide information towards developing a good management plan for clearing C. agatiflora should the data indicate that it may be a significant threat. More than thirty populations of this species were recorded in the country and mapped. Five populations were selected to measure and count the number of individuals, analyse the soil to determine the seed bank and test the seeds for viability and germination. The potential future distribution of the species was modelled based on climatic suitability using MaxEnt to visualise the potential suitable range and ArcGIS to calculate (quantify) the expansion or reduction range of suitability between the current and future climate conditions. We also used the Australian weed risk assessment model to score (quantify) the invasiveness of this species. Furthermore, isozyme studies were done to distinguish whether a single or multiple introductions are responsible for the presence of this species in South Africa. Soil seed bank and records of occurrence show that Crotalaria agatiflora is a slow but persistent invader. Its seed coat dormancy and ability to re-sprout makes it very persistent. One hundred percent (100%) viability and germination was acquired from tested seeds with a very high potential of invasiveness from the Australian model and climate suitability. From the isozyme study it was discovered that there is no variation between populations leading us to believe that, the species has spread from a single introduction. The scientific data obtained from this study show that C. agatiflora poses a significant threat to the flora of South Africa and that it should be controlled. However, it remains to be seen whether eradication is feasible.