The Increased Potential for Aeolian Transport Following Wildfire

Wildfire effects can increase erosivity and erodibility in rangeland soil surfaces. Our objective is to examine controls on the longevity of increased potential for aeolian transport following wildfire. We present results from our ongoing research of 2007 and 2008 wildfires in loess soils of southeastern Idaho. We simultaneously monitored: saltation activity, threshold wind speeds (critical threshold), hydroclimatological variables, and horizontal sediment mass transport, at burned and unburned sites. Review of previous studies indicates that horizontal transport in burned rangeland can exceed that in unburned by 1-3 orders of magnitude, and reveals that research to-date has focused on predominantly sandy soils in warm desert and continental climates. Review also provides examples of temporal variability in erodibility and transport, highlighting a trend towards stabilization following burning that is generally attributed to regrowth of vegetation. Results from our research suggest that the magnitude by which horizontal transport in burned rangelands exceeds that in unburned rangelands in cold desert loess soils is consistent with previous studies. Horizontal transport decreased with time following the wildfires in both years. This corresponded with a decrease in erodibility (increase in critical threshold). Over the course of an entire year following late-summer wildfire, findings of our research suggest that the potential for aeolian transport is greatest during the fall months following wildfire. Soil and atmospheric moisture, furthermore, explain significant variability in erodibility during these fall months. The accumulation of snow in winter and the subsequent emergence of herbaceous vegetation in spring, can return post-fire transport potential to levels similar to those observed in unburned rangelands. These findings suggest that vegetation and hydroclimatology provide important controls on the magnitude and longevity of aeolian transport following wildfire, and are particularly relevant for land restoration specialists.