Targeting forest management through fire and erosion modelling

Abstract

Forests deliver a number of important ecosystem services, including clean water. When forests are disturbed by wildfire, the timing, quantity and quality of runoff are altered. A modelling study was conducted in a forested watershed in California, USA, to determine the risk of wildfire, and the potential post-fire sediment delivery from ~4-ha hillslope polygons within a 1500-km2 basin following a wildfire event. Wildfire intensity was estimated with fire spread models. The estimation of soil burn severity was based on predicted flame length. Sediment delivery was estimated from each hillslope polygon using a Geographic Information System erosion model. Polygons that generated the greatest amount of sediment, affected other values at risk in the basin, or were critical for reducing fire spread were ‘treated’ by reducing the amount and type of fuel available for a wildfire. The fire and erosion models were run a second time for treated conditions to see whether the treatment resulted in a reduced fire intensity and probability, and hence a reduced erosion rate. The estimated erosion rates the first year after the fire dropped from 46 Mg ha–1 before treatment to 26 Mg ha–1 for polygons that had received fuel treatments.