PLANT-SOIL INTERACTIONS IN DESERTS

Geostatistical analyses show that the distribution of soil N, P and K is strongly associated with the presence of shrubs in desert habitats. Shrubs concentrate the biogeochemical cycle of these elements in 'isl ands of fertility' that are localized beneath their canopies, while ad jacent barren, intershrub spaces are comparatively devoid of biotic ac tivity. Both physical and biological processes are involved in the for mation of shrub islands. Losses of semiarid grassland in favor of inva ding shrubs initiate these changes in the distribution of soil nutrien ts, which may promote the further invasion and persistence of shrubs a nd cause potential feedbacks between desertification and the Earth's c limate system.