The overall goal of this SERDP Exploratory Development (SEED) project was to investigate whether specific shrub and tree species distributed along the first-order channels draining desert piedmonts can provide efficient and reliable signals of landscape change and ecological condition. Specific objectives were to: (1) determine the historic range in variation of selected desert vegetation common to alluvial fan surfaces and first-order channels; (2) evaluate if changes in soil and surface hydrology, resulting from either land use activities or natural environmental variation, could be shown to predominantly account for changes in ecosystem condition; and (3) provide recommendations for further developing and testing procedures that can be used to monitor ecosystem status and identify impacts.

Oblique aerial view of a typical desert piedmont in the lower Colorado River region of the Sonoran Desert. Nearly all of the biomass and biodiversity are located along ephemeral washes that are marginal to areas of soils covered with desert pavement.

Six first-order basins were studied ranging in size from approximately 10,000–48,000 m². These basins had a nearly continuous cover of desert pavement prior to any disturbance. Natural and impacted basins were paired geographically to ensure similar soil and climatic conditions. The soil and surface cover of these basins, as well as the limitation of vegetation to drainage channels, was representative of land surface conditions in arid and hyperarid regions of the Southwest and the world. Soil and geomorphic measurements and analysis provided insights into the spatial distribution of soil moisture and the soil properties that impact soil water and vegetation. Methods and standard laboratory investigations data were provided on the volume of surface runoff per precipitation event and the extent of the hydrologic connection between surface anomalies and surface drainage. Biologic characterizations included study of species common to this area—creosotebush, ironwood, and blue paloverde.

Understanding physical and biological signals that indicate change in the flux and availability of water will improve the management of sensitive desert lands. This project advanced the knowledge of fundamental soil-hydrology-vegetation processes that are common to desert piedmonts. Evaluation of critical linkages between soils, soil water balance, and desert plant ecology provides key information about the impact of water availability on desert shrubs, soils, and archeological sites. 

(SEED Project Completion - 2004)