THE DYNAMIC INTERACTION OF CLIMATE, VEGETATION, AND DUST EMISSION, MOJAVE DESERT, USA
Authors: Frank E. Urban, Richard L. Reynolds and Robert Fulton
Abstract: Sparsely vegetated drylands are an important source for dust emission, but little is known in detail about dust generation in response to timing of precipitation and the consequent effects on soil and vegetation dynamics in these settings. This deficiency is especially acute at intermediate landscape scale, a few tens of meters to a several hundred meters. It is essential to consider dust emission at this scale, because it links dust generation at scales of grains and wind tunnels with regional-scale dust examined using remotely sensed data from satellites. Three sites of slightly different geomorphic settings in the vicinity of Soda (dry) Lake were instrumented (in 1999) with meteorological and sediment transport sensors to measure wind erosion through saltating particle detection during high winds. Changes in vegetation in close proximity to the instrumented sites were bi-annually documented through measurements of plant type, cover, and repeat photographic imagery. A succession of dry and wet years has allowed documentation of the profound influence of precipitation-driven annual plant growth (both living and remnant) on variability in dust emission. High levels of precipitation (relative to our period of record) during late winter/early spring 2001 stimulated heavy localized growth of annual grasses, shutting down dust emission at the sites within a period of three months. The year 2002 was very dry with little precipitation or plant growth, yet remnant dead grasses from the previous year continued to stabilize the surface and suppress dust emission for about three months. Modest renewal of particle saltation occurred in late 2002. During early spring 2003, all of 2004, and winter/spring 2005, heavy precipitation stimulated excessive localized plant growth including an extraordinary bloom of an invasive mustard species at one site and mediterranean grass at another. The three-year succession of strong annual vegetation growth dramatically suppressed particle saltation and associated local dust emission. In 2006 and through most of 2007, relatively low precipitation, less vigorous vegetation growth, and gradual disintegration of remnant vegetation cover initiated a strong resurgence of particle saltation by spring 2007. This resurgence came to an end when several heavy precipitation events in the fall of 2007 stimulated vegetation growth that shut down dust emission within a period of about two months. The stable, non-emissive conditions, maintained by stands of remnant vegetation continued through summer 2008. The nine-year record at these sites spans multiple cycles of wet and dry conditions, thus allowing a detailed analysis of the lags and mediating influence that precipitation driven annual plant growth and decay exerts on dust emission in sparsely vegetated drylands.