Ecological biogeomorphology: Metaanalysis of post-fire wind erosion in sagebrush steppe

Background/Question/Methods

Wind erosion of soil following the removal of protective vegetation cover by fire is an increasing problem in semiarid landscapes. Wind erosion can culminate in large losses of soil, impacts to local site fertility, and degradation of downwind airsheds.  Soil stability is highly variable among and within burn sites, and a need to understand and predict likelihood of erosion is a land management need. The purpose of this presentation is to compare and contrast patterns of post-fire wind erosion for eight summer wildfires in the northern Great Basin USA from 2002-2010.  Information on fire size, vegetation condition, and time-since-previous fire were related to amount of soil erosion determined though erosion bridge and sediment collectors (BSNEs).  Fire sizes varied from 100 to >200,000 acres, and were on relatively flat terrain having silty to sandy loam soils.  Data sources included published data, re-calculations of published data, and new data.

Results/Conclusions

Erosion appeared absent or minimal on burn sites smaller than 1000 acres.  On larger sites, erosion was measurable and significant for the late summer to winter and spring periods prior to recovery of protective vegetation cover or snowpack.  The largest burn site (Crystal fire, 220K acres) had ca. 50% herb cover in the summer following fire, which likely related to relatively high cover of perennial bunchgrasses before the fire.  The largest erosion amounts were observed on the 100K acres Jefferson fire, with horizontal saltation fluxes near 125 kg/m/d and several cm of soil loss.  High stem densities and other evidence suggested this site had high shrub cover and few perennial grasses before fire.  Burn sites that had also burned several years earlier had relatively low fluxes (<4 kg/m/d) than sites that had not burned in recent history (15 kg/m/d).  These preliminary findings suggest that fire size, pre-fire vegetation condition, and time-since previous fire are indictors of the likelihood of post-fire wind erosion.  Large burn areas and a high ratio of shrub:bunchgrass cover are factors that relate to landscape condition and livestock use, and their consideration is likely important for predictive models of wind erosion in this ecosystem type.