Post‐fire runoff and erosion from rainfall simulation: contrasting forests with shrublands and grasslands

Abstract

Abstract:Rainfall simulations allow for controlled comparisons of runoff and erosion among ecosystems and land cover conditions. Runoff and erosion can increase greatly following fire, yet there are few rainfall simulation studies for post-fire plots, particularly after severe fire in semiarid forest. We conducted rainfall simulations shortly after a severe fire (Cerro Grande) in ponderosa pine forest near Los Alamos, New Mexico, USA, which completely burned organic ground cover and exposed unprotected soil. Measurements on burned plots showed 74% of mineral soil was exposed compared with an estimated 3% exposed prior to the fire. Most of the remaining 26% surface area was covered by easily moveable ash. Rainfall was applied at 60 mm h 1 in three repeated tests over 2 days. Runoff from burned plots was about 45% of the total 120 mm of applied precipitation, but only 23% on the unburned plots. The most striking difference between the response of burned and unburned plots was the amount of sediment production; burned plots generated 25 times more sediment than unburned plots (76 kg ha 1 and 3 kg ha 1 respectively per millimetre of rain). Sediment yields were well correlated with percentage bare soil (r D 0Ð84). These sediment yields were more than an order of magnitude greater than nearly all comparable rainfall simulation studies conducted on burned plots in the USA, most of which have been in grasslands or shrublands. A synthesis of comparable studies suggests that an erosion threshold is reached as the amount of soil exposed by fire increases to 60-70%. Our results provide sediment yield and runoff data from severely burned surfaces, a condition for which little rainfall simulation data exist. Further, our results contrast post-fire hydrologic responses in forests with those in grasslands and shrublands. These results can be applied to problems concerning post-fire erosion, flooding, contaminant transport, and development of associated remediation strategies.

Effects of wildfire on catchment runoff response: a modelling approach to detect changes in snow-dominated forested catchments

“…Cumulatively, these effects can increase runoff, peak flow magnitude, flooding, surface erosion, sediment delivery to channels, channel bed and bank erosion, sediment concentration, turbidity and potentially soil mass movements including debris flows (Helvey 1980;Swanson 1981;Johansen et al 2001;Conedera et al 2003;Wondzell & King 2003;Lane et al 2006). …”

Effectiveness of three post‐fire rehabilitation treatments in the Colorado Front Range

“…In coniferous forest and chaparral ecosystems, moderate-and high-severity fires can induce a water-repellent layer at or below the soil surface, and this can greatly reduce the infiltration rate (DeBano, 1981;Imeson et al, 1992). The loss of ground cover by burning increases rain-splash erosion, may induce soil sealing, decreases surface roughness, and reduces the time to initial runoff (DeBano et al, 1998;Johansen et al, 2001). By removing most or all of the vegetative, litter, and duff cover, high-severity wildfires reduce water losses through interception and transpiration, and this can further increase runoff.…”

Index for Characterizing Post-Fire Soil Environments in Temperate Coniferous Forests

“…The next threshold (categories 2.0 and 3.0) is for areas that have between 0% and 85% surface organic material. Literature on post-fire erosion and hydrophobic soils identifies thresholds across a range of surface organic material percentages (30%, [50]; 40%, [51]; 45%, [54]; 50%, [52]) from which we selected the median (40%) to divide the categories where 2.0 is 40-85% and 3.0 is less than 40%. We further categorized them by mineral soil char color using a decimal.…”

“…Common soil physical properties influenced by fire include water repellency, structure stability, texture, color, post-fire surface temperatures, and abundance of surface organic material [48] (Table 3). Typically erosion only occurs when organic cover is less than 40-50% after a fire [50][51][52]54]. Therefore, if slopes are steep and coarse textured soils are present, post-fire soil erosion is likely to occur in areas with PFI categories of 3.0 to 4.0.…”