干旱区生态环境知识资源中心

The farm Gamis is located about 250 km SW from Windhoek at the edge of the Namib. Mean annual precipitation is 180 mm with enormous fluctuations in space and time. Extensive pastoral agriculture is supposed to be the suitable type of land use in this ecologically sensitive region where much of the land is now degraded due to overgrazing in the past. At the Gamis farm Karakul sheep are kept for the production of furs. The farmland (30 000 ha) is divided into 98 paddocks, approximately 60 of them are used for the grazing of (up to three) fur production necks. A sophisticated grazing rotation system has prevented the land from degradation, at the same lime guaranteeing the farm's economic survival. We regard this management strategy as an example of sustainable land use. Our computer simulation model is constructed in order to understand the basis of this strategy's success and to apply this knowledge to other situations. The model is a top down approach that simulates rainfall and development of the vegetation according to longterm observations by the farmer. Rules of the rotation system have been included into the model. Variations of the rules are analyzed to compare different strategies. Model results show that the farmer's strategy is able to cope with aridity in general and particularly with the typical occurrence of periods of drought to be found in this region. Alternative strategies are found to be less successful.