Fire effects on rangeland hydrology and erosion in a steep sagebrush-dominated landscape

Pierson, F.B.; Robichaud, P.R.; Moffet, C.A.; Spaeth, K.E.; Hardegree, S.P.; Clark, P.E.; Williams, C.J. 2008. Fire effects on rangeland hydrology and erosion in a steep sagebrush-dominated landscape. Hydrological Processes 22: 2916-2929.

Keywords: erosion; fire; infiltration; interrill; rangeland; rills; runoff; sagebrush; water-repellent soils

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Abstract: Post-fire runoff and erosion from wildlands has been well researched, but few studies have researched the degree of control exerted by fire on rangeland hydrology and erosion processes. Furthermore, the spatial continuity and temporal persistence of wildfire impacts on rangeland hydrology and erosion are not well understood. Small-plot rainfall and concentrated flow simulations were applied to unburned and severely burned hillslopes to determine the spatial continuity and persistence of fire-induced impacts on runoff and erosion by interrill and rill processes on steep sagebrush-dominated sites. Runoff and erosion were measured immediately following and each of 3 years post-wildfire. Spatial and temporal variability in post-fire hydrologic and erosional responses were compared with runoff and erosion measured under unburned conditions. Results from interrill simulations indicate fire-induced impacts were predominantly on coppice microsites and that fire influenced interrill sediment yield more than runoff. Interrill runoff was nearly unchanged by burning, but 3-year cumulative interrill sediment yield on burned hillslopes (50 g m^-2) was twice that of unburned hillslopes (25 g m^-2). The greatest impact of fire was on the dynamics of runoff once overland flow began. Reduced ground cover on burned hillslopes allowed overland flow to concentrate into rills. The 3-year cumulative runoff from concentrated flow simulations on burned hillslopes (298 l) was nearly 20 times that measured on unburned hillslopes (16 l). The 3-year cumulative sediment yield from concentrated flow on burned and unburned hillslopes was 20 400 g m^-2 and 6 g m^-2 respectively. Fire effects on runoff generation and sediment were greatly reduced, but remained, 3 years post-fire. The results indicate that the impacts of fire on runoff and erosion from severely burned steep sagebrush landscapes vary significantly by microsite and process, exhibiting seasonal fluctuation in degree, and that fire-induced increases in runoff and erosion may require more than 3 years to return to background levels.

Moscow FSL publication no. 2008e