6. Tree-Ring Reconstructions of Fire and Climate History in the Sierra Nevada and Southwestern United States

Most of the fire history research conducted in the past century has focused on case studies and local-scale assessments of pattern and process, with an emphasis on describing typical fire frequencies in forest stands and watersheds. Dominant research themes have included the characterization and analyses of fire frequencies across ranges of topographic settings and habitats. In general, these “histories” have been more about describing time-averaged processes, than elucidating the events, narratives, and contingencies of “history.” Now that many crossdated fire chronologies have been developed from tree-ring analyses of firescarred trees, it is possible to assemble regional to global-scale networks of fire occurrence time series. These networks and time series can be used in quantitative, historical analyses that identify and separate broad-scale climate-driven patterns of fire occurrence from local, nonclimatic features of individual sites. The seasonal to annual resolution of tree rings facilitates historical fire climatology because the high temporal resolution of these data allows us to connect multiple events in space and time. The importance of climatic influence is reflected in the degree of synchrony in specific fire events and decadal to centennial trends among widely distributed sites (Swetnam and Betancourt 1990, 1998; Swetnam 1993; Veblen et al. 1999; Veblen, Kitzberger, and Donnegan 2000; GrissinoMayer and Swetnam 1997, 2000; Heyerdahl, Brubaker, and Agee 2001, in press; Kitzberger and Veblen 1998; Kitzberger, Veblen, and Villalba 1997; Kitzberger, Swetnam, and Veblen 2001; Brown, Kaufmann, and Shepperd 1999; Brown et al. 2001; Allen 2002).