Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems

Arid ecosystems cover about 40% of Earth's land area and are home to over two billion people, yet they remain vulnerable to climate change and human actions. Using numerical simulations, and data from Mediterranean ecosystems in Spain, Morocco and Greece, Kéfi et al. show that patch-size distribution of vegetation follows a power law. As grazing pressure increases, patch size deviates from the power law close to the transition to desert conditions. So patch-size distribution may be a useful early warning of desertification. The cover shows an arid landscape (top) in the El Planerón nature reserve in Belchite, Spain, and the lower panels show degradation in this landscape. In a separate paper, Scanlon et al. use satellite imagery to show that the size distribution of tree clusters in the Kalahari basin also follows a scale-free power law. This can be explained by positive feedback associated with preferential environments near existing trees. In News & Views Ricard Solé discusses both papers.