Skip to main content
No Access

Spatial Heterogeneity and Irreversible Vegetation Change in Semiarid Grazing Systems

1. Tropical Nature Conservation and Vertebrate Ecology Group, Wageningen University, Bornsesteeg 69, 6708 PD Wageningen, Netherlands;2. Department of Plant Biology, University of Groningen, P.O. Box 40, 9750 AA Haren, Netherlands;3. Erosion and Soil and Water Conservation Group, Wageningen University, Nieuwe Kanaal 11, 6709 PA Wageningen, Netherlands;4. Plant Production Systems Group, Wageningen University, P.O. Box 430, 6700 AK Wageningen, Netherlands;5. School of Mathematics, Statistics, and Information Technology, University of Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa;6. International Institute for Aerospace Survey and Earth Sciences, Hengelosestraat 99, P.O. Box 6, 7500 AA Enschede, Netherlands;7. Swiss Federal Institute for Environmental Science and Technology, Seestrasse 79, CH‐6047 Kastanienbaum, Switzerland;8. Department of Zoology, University of Guelph, Guelph, Ontario N1G 2W1, Canada

Recent theoretical studies have shown that spatial redistribution of surface water may explain the occurrence of patterns of alternating vegetated and degraded patches in semiarid grasslands. These results implied, however, that spatial redistribution processes cannot explain the collapse of production on coarser scales observed in these systems. We present a spatially explicit vegetation model to investigate possible mechanisms explaining irreversible vegetation collapse on coarse spatial scales. The model results indicate that the dynamics of vegetation on coarse scales are determined by the interaction of two spatial feedback processes. Loss of plant cover in a certain area results in increased availability of water in remaining vegetated patches through run‐on of surface water, promoting within‐patch plant production. Hence, spatial redistribution of surface water creates negative feedback between reduced plant cover and increased plant growth in remaining vegetation. Reduced plant cover, however, results in focusing of herbivore grazing in the remaining vegetation. Hence, redistribution of herbivores creates positive feedback between reduced plant cover and increased losses due to grazing in remaining vegetated patches, leading to collapse of the entire vegetation. This may explain irreversible vegetation shifts in semiarid grasslands on coarse spatial scales.