El Nino as a window of opportunity for the restoration of degraded arid ecosystems

Most arid ecosystems have suffered from severe overexploitation by excessiv e wood harvesting, overgrazing, and agriculture, resulting in depletion of vegetation biomass and soil erosion. These changes are often difficult to r everse due to positive feedbacks that tend to stabilize the new situation. In this paper, we briefly review evidence for the idea that different state s in these ecosystems might represent alternative equilibria and present a graphic model that summarizes the implications for their response to changi ng environmental conditions. We show how, in the light of this theoretical framework, climatic oscillations such as El Nino Southern Oscillation (ENSO ) could be used in combination with grazer control to restore degraded arid ecosystems. We also present evidence that, depending on grazing pressure, ENSO episodes can trigger structural and long-lasting changes in these ecos ystems.