Prescribed‐fire effects on rill and interrill runoff and erosion in a mountainous sagebrush landscape

Abstract

Changing fire regimes and prescribed-fire use in invasive species management on rangelands require improved understanding of fire effects on runoff and erosion from steeply sloping sagebrush-steppe. Small (0·5 m 2 ) and large (32·5 m 2 ) plot rainfall simulations (85 mm h -1 , 1 h) and concentrated flow methodologies were employed immediately following burning and 1 and 2 years post-fire to investigate infiltration, runoff and erosion from interrill (rainsplash, sheetwash) and rill (concentrated flow) processes on unburned and burned areas of a steeply sloped sagebrush site on coarse-textured soils. Soil water repellency and vegetation were assessed to infer relationships in soil and vegetation factors that influence runoff and erosion. Runoff and erosion from rainfall simulations and concentrated flow experiments increased immediately following burning. Runoff returned to near pre-burn levels and sediment yield was greatly reduced with ground cover recovery to 40 per cent 1 year post-fire. Erosion remained above pre-burn levels on large rainfall simulation and concentrated flow plots until ground cover reached 60 per cent two growing seasons post-fire. The greatest impact of the fire was the threefold reduction of ground cover. Removal of vegetation and ground cover and the influence of pre-existing strong soil-water repellency increased the spatial continuity of overland flow, reduced runoff and sediment filtering effects of vegetation and ground cover, and facilitated increased velocity and transport capacity of overland flow. Small plot rainfall simulations suggest ground cover recovery to 40 per cent probably protected the site from low-return-interval storms, large plot rainfall and concentrated flow experiments indicate the site remained susceptible to elevated erosion rates during high-intensity or long duration events until ground cover levels reached 60 per cent. The data demonstrate that the persistence of fire effects on steeply-sloped, sandy sagebrush sites depends on the time period required for ground cover to recover to near 60 per cent and on the strength and persistence of 'background' or fire-induced soil water repellency. Published in

Characterization and evaluation of controls on post-fire streamflow response across western US watersheds

“…For example, studies in rangeland regions of the US found moderate increases in flow, infiltration, and erosion rates after major wildfires, with trends continuing for as long as 15 years (Emmerich and Cox, 1994;Pierson et al, 2009;Hester et al, 1997;Kinoshita and Hogue, 2015). Fires in chaparral environments, such as in southern California, exhibited increased flows of up to as much as 2 orders of magnitude, with much of this occurring in the dry season (Coombs and Melack, 2013;Hogue, 2011, 2015;Loáiciga et al, 2001).…”

Post-wildfire Erosion in Mountainous Terrain Leads to Rapid and Major Redistribution of Soil Organic Carbon

“…The amount of material mobilized in a particular watershed is dependent on the intensity and duration of rainfall, groundcover, vegetation, slope gradient, and recent fire history (Renard et al, 1997;Pierson et al, 2009). Between 70 and 90% of the soil and associated carbon mobilized from eroding landscapes is deposited within the source or adjacent watersheds (Gregorich et al, 1998;Stallard, 1998).…”

“…The loss of vegetation after high severity fires is one of the main drivers of post-fire erosion, as vegetation plays a major role in stabilizing eroding soils (Shakesby et al, 1993;Larsen et al, 2009;Pierson et al, 2009). In extreme cases, this loss of vegetation can lead to debris and ash flows when intense rainfall events occur on recently burned hillslopes .…”

Evaluating rehabilitation efforts following the Milford Flat Fire: successes, failures, and controlling factors

“…First, disturbance by heavy equipment during rehabilitation can negatively impact any desired species that survived the wildfire. Second, and most importantly, disturbing a post-fire landscape can result in accelerated soil erosion (Pierson et al 2009, Miller et al 2012. Wildfires typically negatively impact surface soil quality through loss of organic matter and exacerbation of hydrophobicity effects (Pierson et al 2014, Williams et al 2014a, resulting in reduced infiltration capacity, increased run-off, and generally poor seed germination (Pierson et al 2002, Ravi et al 2006, 2007, Pierson et al 2011.…”

“…Wildfires typically negatively impact surface soil quality through loss of organic matter and exacerbation of hydrophobicity effects (Pierson et al 2014, Williams et al 2014a, resulting in reduced infiltration capacity, increased run-off, and generally poor seed germination (Pierson et al 2002, Ravi et al 2006, 2007, Pierson et al 2011. However, the loss of vegetation cover from wildfire leaves these soils exposed to erosion by wind and water (Pierson et al 2009), and disturbing these soil surfaces further during post-fire rehabilitation can greatly increase soil erodibility (Williams et al 2014b). …”