ABSTRACT
Soil erosion is a three-part process consisting of detachment, transport, and deposition of soil particles. All of these processes are controlled by erosive energy and soil properties, which can be either directly or indirectly affected by wildfire. These post-fire changes often lead to erosion rates that are several orders of magnitude greater than in forested environments which have adequate vegetation and forest floor material protecting the mineral soil. Concentrated overland flow or rill flow is one of the main hillslope erosion processes after wildfires. Since the forest floor is often consumed, overland flow velocities increase due to the reduced surface roughness, allowing for greater sediment transport capacity. The result is both increased overland flow and erosion. Erosion of hillslopes, the formation of rills, and the incision of gullies and stream channels produces high concentrations of sediment that can result in sediment-rich flood events such as debris floods and debris flows. However, the erosional response to wildfires is highly variable and reflects the specific site characteristics, such as watershed area, topography, and rainfall characteristics (e.g., intensity and duration) in combination with the severity of the fire and its effects on the forest floor and soil properties. Therefore, the change in the amount of erosion resulting from a wildfire will depend on the soil burn severity including: the proportion of exposed mineral soil and the quality of any remaining forest floor; the degree of soil heating and presence of soil water repellency that may increase runoff; the physiographic factors such as drainage and slope characteristics that may influence erosion energy and concentration times of surface water runoff; and the inherent erosivity of the site, in particular the probability of high
intensity rainstorms in the first years after fire. Some forms of gravitydriven erosion, namely dry ravel and mass failures, are also important in some areas. Wind erosion is less common, though it may be significant in drier environments with erodible soils.
