Examining historical and current mixed-severity fire regimes in ponderosa pine and mixed-conifer forests of western North America.
There is widespread concern that fire exclusion has led to an unprecedented threat of uncharacteristically severe fires in ponderosa pine (Pinus ponderosa Dougl. ex. Laws) and mixed-conifer forests of western North America. These extensive montane forests are considered to be adapted to a low/moderate-severity fire regime that maintained stands of relatively old trees. However, there is increasing recognition from landscape-scale assessments that, prior to any significant effects of fire exclusion, fires and forest structure were more variable in these forests. Biota in these forests are also dependent on the resources made available by higher-severity fire. A better understanding of historical fire regimes in the ponderosa pine and mixed-conifer forests of western North America is therefore needed to define reference conditions and help maintain characteristic ecological diversity of these systems. We compiled landscape-scale evidence of historical fire severity patterns in the ponderosa pine and mixed-conifer forests from published literature sources and stand ages available from the Forest Inventory and Analysis program in the USA. The consensus from this evidence is that the traditional reference conditions of low-severity fire regimes are inaccurate for most forests of western North America. Instead, most forests appear to have been characterized by mixed-severity fire that included ecologically significant amounts of weather-driven, high-severity fire. Diverse forests in different stages of succession, with a high proportion in relatively young stages, occurred prior to fire exclusion. Over the past century, successional diversity created by fire decreased. Our findings suggest that ecological management goals that incorporate successional diversity created by fire may support characteristic biodiversity, whereas current attempts to "restore" forests to open, low-severity fire conditions may not align with historical reference conditions in most ponderosa pine and mixed-conifer forests of western North America.
Earth Research Institute, University of California Santa Barbara, Santa Barbara, California, United States of America ; Environmental Studies Department, Southern Oregon University, Ashland, Oregon, United States of America.
Dennis C
DC
Odion
Earth Island Institute, Berkeley, California, United States of America.
Chad T
CT
Hanson
Canadian Forest Service Natural Resources Canada, Corner Brook, N.L., Canada.
André
A
Arsenault
Program in Ecology and Department of Geography, University of Wyoming, Laramie, Wyoming, United States of America.
William L
WL
Baker
Geos Institute, Ashland, Oregon, United States of America.
Dominick A
DA
Dellasala
Avian Science Center, Division of Biological Sciences, University of Montana, Missoula, Montana, United States of America.
Richard L
RL
Hutto
Wildlife Habitat Ecologist, FLNR, Thompson-Okanagan Region, Kamloops, B.C., Canada.
Walt
W
Klenner
Ecosystem Sciences Division, Environmental Science, Policy, & Management Dept., University of California, Berkeley, California, United States of America.
Max A
MA
Moritz
Department of Geography, Humboldt State University, Arcata, California, United States of America.
Rosemary L
RL
Sherriff
Department of Geography, University of Colorado Boulder, Boulder, Colorado, United States of America.
Thomas T
TT
Veblen
Program in Ecology and Department of Geography, University of Wyoming, Laramie, Wyoming, United States of America.
Mark A
MA
Williams
D017753:Ecosystem; D005390:Fires / Q000266:history*; D016468:Forestry / Q000379:methods*; D049672:History, 19th Century; D049673:History, 20th Century; D049674:History, 21st Century; D009656:North America; D041604:Pinus ponderosa / Q000502:physiology*; D064028:Tracheophyta / Q000502:physiology*; D014887:Weather