Dust supply varies with sagebrush microsites and time since burning in experimental erosion events

Abstract

Wind erosion and large dust plumes are an increasingly important attribute in cold-desert rangelands, particularly as wildfire increases. Fire reduces vegetation, which increases erosivity. Whether sediment supply increases after fire has not been determined in this environment. We asked how sediment supply varied among sites burned 2-months to 5-years previously, in comparison to unburned sagebrush steppe, across 500 km of southern Idaho, USA. We measured potential dust emissions (PM10, particles <10 μm diameter) in response to step changes in friction velocity (u *), with a field-based wind tunnel analog (PI-SWERL, Portable In Situ Wind Erosion Laboratory). We evaluated how emissions, sediment supply, and a proxy of erodibility varied among the microsite soil patterning in these sites (shrub islands and interspaces). Emissions were three orders of magnitude greater on burned compared to unburned surfaces, especially where shrubs had existed and sites burned more recently. Greater emission rates were due to greater sediment supply, whereas the proxy of erodibility did not vary among the surfaces for dry conditions that prevail during large wind erosion events (near -150 MPa at the surface). Wetter surface conditions, similar to those after precipitation or snowmelt, resulted in less dust emission on a recently burned site. Dust supply increases in initial postfire years especially on microsites that previously had shrubs. Abundance of shrubs is responsive to management practices that affect prefire vegetation, and grazing-induced increases in shrubs might, for example, render a site more vulnerable to dust emissions following fire. Copyright 2012 by the American Geophysical Union.