Influence of humans and climate on the fire history of a ponderosa pine-mixed conifer forest in the southeastern Klamath Mountains, California

Abstract

Fire history of a ponderosa pine-mixed conifer forest was investigated in the Whiskeytown National Recreation Area, southeastern Klamath Mountains, California. Fire return intervals were found to be frequent and similar to other comparable forests in California. Median fire interval for the six sample plots (1.4–1.7 ha) ranged from 2 to 4 years (mean range, 4.8–7.4 years). Most fires (93%) occurred late in the growing season or after growth for the season had stopped. Early fire activity was frequent and heterogeneous; however, this trend dramatically changed ca. 1850 to a less frequent and more homogeneous fire pattern. Euro-American settlement, which was active in this area, most likely caused this change by the elimination of Native American ignitions and by introducing logging, gold mining, grazing, and early fire suppression. For the period of record (1750–2002), years when fires were widespread within the study area were not correlated with drought conditions represented by reconstructed climate indices: palmer drought severity index (PDSI) and southern oscillation index. After 1850 when Euro-American settlement began, widespread fire years were associated with wetter than average conditions 3 years preceding the fire year (PDSI, gridpoint #5). Although several recent fire history studies have identified fire–climate relationships with these indices in the Pacific Northwest, additional research is needed in the southern portion of the region. Possible future extensions from the fire–climate relationships identified include: anticipating wildfire extent for future fire seasons, understanding potential alterations in Klamath fire regimes forced by climate change or by cultural land use practices, as well as planning fire management activities (fuels reduction, prescribed fire, etc.).