Abstract
M.Sc. (Botany)
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, KwaZulu-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 information can be provided for developing a good management plan for clearing C. agatiflora in South Africa.
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 ability. 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. The Australian weed risk assessment model was also used to score (quantify) the invasiveness of this species. Furthermore, isozyme studies were done to determine whether a single or multiple introductions are responsible for the presence of this species in South Africa.
The soil-stored seed bank and records of occurrence show that C. agatiflora is a slow but persistent invader. Its seed coat dormancy and ability to re-sprout makes it very persistent. Seed germination tests showed 100% viability. A very high potential of invasiveness was indicated by the Australian weed risk assessment and the climate suitability models. The isozyme study showed no variation between populations indicating that the species has most likely 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. The data will inform management plans of the Invasive Species Programme of the South African Biodiversity Institute.