Northwest California National Forests fire severity monitoring 1987-2008

Abstract

Research in the last several years has indicated that the frequency of large fires is on the rise in western US forests. Although fire size and frequency are important, they do not necessarily provide information concerning the effects of fire on ecosystems, as ecosystems differ in ecological and evolutionary relationships with fire. Our study focused on the four National Forests of NW California (Klamath, Mendocino, Shasta-Trinity, and Six Rivers). We assessed: 1) trends and patterns in fire size and frequency from 1910-2008 (all fires >40 ha), and 2) percentage of high-severity in fires from 1987-2008 (all fires >400 ha). During 1910-2008 the mean and maximum fire size and total annual area burned increased, yet we found no trend in percentage of high-severity during 1987-2008. The time series of severity data was strongly influenced by four years (1987, 1999, 2006, 2008) with region-wide lightning events that burned huge areas at primarily low to moderate severity. Following decades of fairly successful fire suppression, the fire rotation across the four National Forests reached a high of 974 yrs in 1984. However, by 2008 the fire rotation had fallen to 95 yrs due to the years of widespread lightning fires. Percentage of high-severity in conifer-dominated forests was generally higher in areas dominated by smaller diameter trees than areas with larger diameter trees. The years with region-wide lightning caused fires were characterized by less winter and spring precipitation than years dominated by smaller human ignited fires. Overall percentage of high-severity was generally less in years characterized by these region-wide lightning events. Our results suggest that under certain conditions wildfires could be more extensively used to achieve ecological and management objectives in NW California.

Citation

Miller, Jay D.; Skinner, Carl N.; Safford, Hugh D.; Knapp, Eric E.; Ramirez, Carlos M. 2012. Northwest California National Forests fire severity monitoring 1987-2008. Publication R5-TP-035 Vallejo, CA: USDA-Forest Service, Pacific Southwest Region. 87 p.