Developing Effective Ecosystem Monitoring Strategies for Military Activities in Deserts: Results from the US Army Yuma Proving Ground.
Eric V. McDonald1, Todd Caldwell1, Erik P. Hamerlynck2, and Valerie Morrill3. (1) Desert Research Institute, 2215 Raggio Pkwy, Reno, NV 89512, (2) Rutgers University, Dept. Biological Sciences, 101 Warren St., Newark, NJ 07102, (3) US Army Yuma Proving Ground, ATTN: CSTE-DTC-YP-CD-ES, 301 C. Street / BLDG 303, Yuma, AZ 85365
Biomass and biodiversity in arid lands is largely associated with vegetation along low order channels that drain alluvial fans a due to considerable increase water derived from ephemeral runoff from the surrounding soils. Any change in runoff supplied water, either as a result of soil degradation related to military activities or a change in seasonal precipitation related to climatic change, will directly impact critical parts of the ecosystem. Recognition of physical and biological signals that indicate change in the flux and availability of water will greatly benefit land rehabilitation and management of sensitive desert lands. The goal of this project was to determine if key shrub and tree species distributed along first-order channels draining desert piedmonts on military reservations can provide cost-effective and reliable signals of environmental change and desert ecosystem health. Our approach integrates essential soil, geomorphic, hydrologic, and biologic characterization data to establish linkages among soil, climate, and vegetation dynamics. Results indicate that trends in vegetation condition are sensitive to changes related to either military activities or natural changes in rainfall. Results also indicate that the vitality of essential tree species along desert washes may be strongly influenced by water derived from infrequent large storms. Spring and mid-summer predawn and midday water potentials achieved in Cercidium (foothills palo verde) and Olneya (desert ironwood) are much higher than could be expected given the very low volumetric moisture content of the soils (< 1m). This suggests that Cercidium and Olneya have access to deep vadose water supplies (not ground water). Infrequent, high energy storms likely provide enough water to generate overland flow and thus sufficiently recharge at deeper soils of channels to sustain plant activity over prolonged periods (i.e. > 1-3 years) where ambient water inputs may not be sufficient to recharge shallower surface layers.