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

Abstract

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. Published in

Effects of wildfires on peak discharges in watersheds

“…For this reason, the unit-area peak discharge is considered to be the most sensitive parameter for the description of the modified watershed response after a wildfire (e.g., Rowe et al 1954). More specifically, experimental analyses conducted both in Europe and in the United States indicate that the annual peak discharge in postfire conditions can increase by a factor generally ranging from 1.2 to 6.5 (Hoyt & Troxell 1934, Anderson 1976, Hessling 1999, Loáiciga et al 2001, Conedera et al 2003, Rulli & Rosso 2007, Pierson et al 2008, Seibert et al 2010 and can even exceed 100 in some cases (Campbell et al 1977, Bolin & Ward 1987, Neary et al 2003. However, there have been some case studies (Britton 1991, Aronica et al 2002, Bart & Hope 2010 in which little or no increase in postfire discharges were observed.…”

Pyrogenic Carbon Erosion: Implications for Stock and Persistence of Pyrogenic Carbon in Soil

“…One study found that interrill sediment erosion was doubled in a burned watershed compared to a neighboring unburned watershed, along with increases in runoff velocity due to increased bare ground coverage (Pierson et al, 2008(Pierson et al, , 2013. The relative extent of interrill compared with rill erosion depends upon local landscape and precipitation conditions, where higher precipitation intensity and steeper slopes can drive increased rill formation (Moody et al, 2013).…”

“…The loss or reduction of vegetation cover due to fires creates the opportunity for raindrops to reach the soil surface at high velocity, without being slowed down by aboveground vegetation and overlying litter layers. Hence, the same amount or intensity of rainfall can mobilize more PyC, and bulk C, from soil post-fire than it would under unburned conditions if there is loss of vegetation or litter layers (Inbar et al, 1998;Beyers et al, 2005;Cerdà and Doerr, 2005;Pierson et al, 2008Pierson et al, , 2009Pierson et al, , 2013. Generally, low intensity precipitation events drive preferential transport of light carbonaceous material (higher enrichment ratios, higher concentration of C) (Schiettecatte et al, 2008;Wang et al, 2010).…”

“…The impacts of aspect on hillslope erosion can be compounded by delays in vegetation recovery, leading to longer-term enhanced erosion rates and continued loss of soil nutrients, and weather-related events, which can cause different erosion rates on different aspects of the same hillslope (Cerdà et al, 1995;Pierson et al, 2008Pierson et al, , 2009). Furthermore, the location within a landscape where PyC is formed or deposited can be critical for the long-term fate of the PyC.…”

Assessment of Site and Soil Characteristics of Rill Erosion Following the Lockheed Fire in the Little Creek Watershed, Swanton Pacific Ranch

“…At these sites, rainfall exceeded the initial infiltration and storage capacity, thus initiating runoff resulting in a high occurrence of rill erosion (Pierson et al, 2008a).…”