A spatially explicit simulation model will be designed which will be used to find explanations for the high species richness in the mountain area of the western Richtersveld. The databases for this model are the permanent plots which are investigated by Norbert Juergens and co-workers since 20 years. Based on this detailed information of position, size and species of plants an individual-based, grid-based simulation model will be constructed which describes the spatial-temporal dynamics of the populations of the dominant species under the influence of the varying weather conditions which are characteristic for this region. The model will be used to determine the processes and factors, which are essential for the co-existence of these plant species. The hypothesis will be tested by the model that the relatively short live span of the plants, the extreme spatial heterogeneity of the soil, the run-off of rain water as well as the recurrent strong droughts are important factors. By comparing the result of this model with the outcome in other (semi-) arid regions general principles and ecosystem specific properties should be revealed.

This project will result in the delivery of a simulation program of the model, which can be extended to similar problems in other similar arid ecosystems by minor modifications. The general understanding produced with this model will provide the basis for giving hints for a sustainable grazing strategy of this area.

Partner in this project is Karen Esler, University Stellenbosch. The project leader, C. Wissel presents a three-week short course on ecological modelling at the University of Cape Town each year.