Desertification in an Arid Shrubland in the Southwestern United States

Abstract

In the Mojave Desert of the southwestern U.S. human destruction of soil crusts and removal of vegetation have led to progressive, expanding degradation of adjacent arid shrublands. Aeolian mobilisation of dust, sand and litter triggered by anthropogenic disturbance contributes to the destruction of islands of fertility in adjacent areas by killing shrubs through burial and abrasion. This interrupts nutrient-accumulation processes and allows the loss of soil resources by abiotic transport. Thus the processes of degradation spread across the landscape driven largely by abiotic processes.

Soil chemical analyses and remote sensing observations presented here are designed to test a model hypothesis of degradation of arid shrublands. Nutrient and non-nutrient chemical species in the soil act as tracers of material transport and provide clues as to the nature of progressive anthropogenic degradation in arid shrublands. Remote sensing yields information about short- and long-term effects on the landscape as well as important constraints on the magnitude of degradation. Field, chemical and remote sensing observations argue for an extension of recent definitions and models of desertification to include the loss of islands of fertility in established shrublands. This extended model places arid shrublands in a continuum of physical and ecological processes and ecosystems that links semiarid grasslands with Sahara-like hyperarid barren lands.