title: Spatial heterogeneity and irreversible vegetation change in semiarid grazing systems.
abstract: 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.
authors: Tropical Nature Conservation and Vertebrate Ecology Group, Wageningen University, Bornsesteeg 69, 6708 PD Wageningen, Netherlands.
authors: Johan
authors: J
authors: van de Koppel
authors: Max
authors: M
authors: Rietkerk
authors: Frank
authors: F
authors: van Langevelde
authors: Lalit
authors: L
authors: Kumar
authors: Christopher A
authors: CA
authors: Klausmeier
authors: John M
authors: JM
authors: Fryxell
authors: John W
authors: JW
authors: Hearne
authors: Jelte
authors: J
authors: van Andel
authors: Nico
authors: N
authors: de Ridder
authors: Andrew
authors: A
authors: Skidmore
authors: Leo
authors: L
authors: Stroosnijder
authors: Herbert H T
authors: HH
authors: Prins