Spatial and temporal evolution of sub-alpine forest fire regimes during the late Holocene, Rocky Mountain National Park, Colorado

Background/Question/Methods

Landscape heterogeneity in subalpine forests is strongly influenced by temporal and spatial patterns of fire. Tree-ring records provide detailed fire history information covering the past 500 years and, in conjunction with paleoclimate records, they illustrate strong climatic controls on fire occurrence at inter-annual to decadal time scales. Little is known, however, about the characteristics of subalpine forest fire regimes at longer time scales or the sensitivity of these regimes to multi-centennial climatic change. We are utilizing pollen and macroscopic charcoal from a network of seven lake-sediment records to describe subalpine forest fire regimes across a 250-km² region in Rocky Mountain National Park since 4000 yr BP (calibrated years before 1950 AD). This period is characterized by the development of modern climate and vegetation in central Colorado and includes important centennial-scale variations in temperature and moisture regimes.

Results/Conclusions

We report results from three records on the east side of the continental divide in Rocky Mountain National Park. Comparisons to previously published tree-ring reconstructions of fire history in the study area indicate the faithfulness of the charcoal records over the past several hundred years. At individual sites, fire return intervals (FRIs) inferred from peaks in charcoal accumulation rates are highly variable, ranging from 50 to > 400 years and reflecting the stochastic nature of local fire occurrence in subalpine forests. Mean FRIs varied little between sites, with values since 2000 yr BP ranging from 160 to 190 years. Prior to 2000 yr BP, mean FRIs were longer, ranging from 210 to 270 years, but not significantly different from the 2000-0 yr BP period at any one site. Ongoing charcoal and pollen analysis on these and additional cores, as well as comparisons to regions paleoclimate records, will help facilitate inferences into the mechanisms controlling historic fire regimes in the study area.