A spatially-explicit reconstruction of historical fire occurrence in the ponderosa pine zone of the Colorado Front Range

A key issue in ecosystem management in the western U.S. is the determination of the historic range of variability of fire and its ecological signif-icance prior to major land-use changes associated with Euro-American settlement. The present study relates spatial variation in historical fire occurrence to variation in abiotic and biotic predictors of fire frequency and severity across the elevational range of ponderosa pine in northern Colorado. Logistic regression was used to relate fire frequency to environmental predictors and to derive a proba-bility surface for mapping purposes. These results indicate that less than 20 % of the ponderosa pine zone had an historic fire regime (pre-1915) of rel-atively frequent fires (mean fire intervals, MFI, <30 years). More than 80 % is reconstructed to have had a lower frequency (MFI ‡ 30 years), more variable severity fire regime. High fire fre-quency is clearly associated with low elevations. Lower and more variable fire frequencies, associ-ated with high and moderate severities, occur across a broad range of elevation and are related to variations in other environmental variables. Only a small part of the ponderosa pine zone fits the widespread view that the historic fire regime was characterized mainly by frequent, low-severity that maintained open conditions. Management at-tempts to restore historic forest structures and/or fire conditions must recognize that infrequent se-vere fires were an important component of the historic fire regime in this cover type in northern Colorado. Key words: fire history; ponderosa pine; Pinus ponderosa; geographic information system; Colo-rado Front Range; fire regime