Distribution and frequency of wildfire in California riparian ecosystems

Although wildfire has been recognized as having important ecological impacts on California's riparian environments, understanding of its occurrence is largely anecdotal, based on studies of fire impacts in scattered locations. In this paper we use data for 21 years of wildfires to examine the distribution, seasonality and climatic context of riparian wildfire across the state. We used the Monitoring Trends in Burn Severity and LANDFIRE databases to identify fires that had burned in areas classified as having riparian vegetation, and matched those fires with the Fire and Resource Assessment Program database to determine the date of occurrence of each. From 1990 through 2010, an average of 1197 ha of riparian vegetation burned per year, which extrapolates to a fire return interval of 843 years. The statewide totals are misleading, however, because there is substantial geographic variance in the occurrence of riparian fire. In southern California ecoregions, extrapolated return intervals are as low as 74 years, contrasting with the Basin and Range ecoregions, where return intervals exceed 1000 years. Moreover, there is substantial geographic variation in the season of riparian fire, and in the relationship between fire occurrence and climatic variables. Both the widespread occurrence of riparian fire and its spatial variability are potentially important for management of critical riparian habitat.