Soil-Plant Relations in the Southwestern United States.

The southwestern USA is dominated by the Basin and Range deserts (Chihuahuan Desert, Sonoran Desert, Mojave Desert, and the southern Great Basin) and the Colorado Plateau. The Basin and Range deserts are dominated by broad valleys, filled primarily with alluvium, separated by mountain ranges. Soils in basins are dominated by Aridisols, which have subsurface accumulations of silicate clay, carbonates, opaline silica, and/or gypsum. While creosote bush is the dominant shrub in the warmer Basin and Range deserts, the Mojave supports Joshua trees, the Sonoran supports relatively high cover of saguaro and other cactus, and the Chihuahuan supports relatively high cover of grasses, which likely reflects the variation in temperature and the amount and seasonal distribution of precipitation. The cooler southern Great Basin is dominated by sagebrush. Vegetation patterns in Basin and Range deserts are linked to the degree of soil development, which depends on geomorphic surface stability and age, and parent material mineralogy and particle-size. Large shrubs are common on deep soils, with smaller statured plants common on soils shallow to a root-restricting layer. In contrast, the Colorado Plateau is a bedrock-controlled landscape dominated by Entisols. Vast parts of the Colorado Plateau are covered by eolian sand. Grasses are common on deep sandy soils, with large shrubs common on shallower soils. As the climate of the southwestern USA is predicted to warm and experience a shift in the seasonal distribution of precipitation, understanding soil-plant relations is essential for adapting land management strategies for maintaining ecosystem health and conserving plant diversity. Examples of soil-plant relations in the southwestern USA will be presented, along with some suggestions for using this information for adapting land management.