The effect of fire-induced soil hydrophobicity on wind erosion in a semiarid grassland: Experimental observations and theoretical framework

Aridland ecosystems are often susceptible to degradation resulting from disturbances like fires and grazing. By exposing the soil surface to the erosive action of winds, these disturbances contribute to the redistribution of soil nutrients associated with grassland-to-shrubland conversions and to the formation of a heterogeneous landscape. Wind erosion maintains the local heterogeneities in nutrient and vegetation distribution in arid landscapes through the removal of nutrient-rich soil from the intercanopy areas and the subsequent deposition of soil onto vegetation patches. Even though wind erosion and disturbances like fires strongly interact with each other and determine vegetation patterns in arid landscapes, very few studies have addressed these interactions. Using soil samples collected after a wildfire event at the Cimarron National Grasslands in southwestern Kansas, we demonstrate through a series of wind-tunnel experiments, laboratory measurements, and theoretical analyses how wind erosion can be enhanced by fire-induced water repellency. Results from the wind-tunnel experiments show that in semiarid grasslands fires can cause a decrease in the threshold velocity of wind erosion thereby, enhancing the post-burn erosion of (hydrophobic) soils. Further, a generalized process-based theoretical equation was derived to explain the decrease in threshold friction velocity in water-repellent soil for the case of soil particles modeled as asymmetrical cones.