Literature Summary Pascal Berrill & Jennifer Potts ESPM 298 Fire Seminar October 2001 UC Berkeley, CA. Fire and Geomorphic Processes F. J. Swanson USDA Forest Service, 1981 Definition: Geomorphology - the branch of geology that studies the characteristics and configuration and evolution of rocks and land forms. Swanson describes various interactions between fire, geomorphic processes and landforms, outlining how fire can influence the shape of landforms and vica versa. In general, increased erosion follows fire; soils are exposed to rainfall upon combustion of ground vegetation and litter, increasing both surface runoff-related erosion and the amount of water held in the soil, which when combined with fire-induced mortality of deeper-rooted species, can lead to mass movement slippage. Sediments and debris accumulate in streams, and are carried downstream, with negative local consequences and flow-on effects. Erosion rate appears greatest in the year immediately following fire, tailing off to background levels over 10 or more years (varies between ecosystems, and with fire intensity/extent) once bare soil is reoccupied and covered by understory vegetation and litter, and reestablished by roots from new overstory species. Young landscapes with steeper terrain are deemed more sensitive to fire disturbance, because: Topography has a greater effect on fire in steeper country, Vegetation plays a greater role in soil stabilization in steeper less-stable terrain. Swanson cites chaparral as one of the most vulnerable landscapes, due to frequent fire return, high fire intensity, steep terrain, and characteristic periods of intense rain. Sediment flows from burnt chaparral catchments can exceed 30 times the normal baseflow of sediments in the year after fire, with fire-accelerated sediment yields contributing over 70% of the long-term sediment yields from these catchments At the other end of the `risk spectrum', NE mixed conifer-hardwood forests on older, stable eroded landscapes with decreased fire frequency have much lower estimated fireaccelerated erosion rates e.g. Southern Ontario where fire-accelerated erosion accounts for less than 6% of long-term yields when fire returns about every 80 years. At an intermediate level of risk, the NW mixed conifer forests are estimated to yield five times the baseflow of sediments immediately after fire, returning to baseflow rates after 20-30 years, with fire-accelarated erosion contributing around 25% of all sediment yield. The key messages appear to be that: 1. Fire-accelerated erosion is highly variable, generally increasing with fire intensity and frequency, and steeper topography, especially where vegetation is largely responsible for erosion control through ground cover and rooting depth/strength. 2. The influences of fire on erosion are difficult and time-consuming to measure accurately, and can be confounded with erosion caused by fire fighting efforts (cutting fire lines) and salvage logging, and associated road construction.