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 "islands of fertility" that are localized benath their canopies, while adjacent barren, intershrub spaces are comparatively devoid of biotic activity. Both physical and biological processes are involved in the formation of shrub islands. Losses of semiarid grassland in favor of invading shrubs initiate these changes in the distribution of soil nutrients, which may promote the further invasion and persistence of shrubs and cause potential feedbacks between desertification and the Earth's climate system.