RELATING HISTORIC FIRE REGIMES TO 20TH-CENTURY FIRE POTENTIAL MAY AUGMENT ECOLOGICAL JUSTIFICATIONS FOR EXPANDED FUEL TREATMENT PROGRAMS

Federal land management agencies in the U.S. have responded to recent severe wildfire seasons with plans to greatly expand fuel treatment programs. These plans are often accompanied by ecological justifications to assuage environmental objections to fuel treatment activities (e.g., tree removal, smoke production). However, the chain of hypotheses that support ecological justifications for fuel treatments has received scant empirical assessment. With the aid of published repeat photography, we present an objective evaluation of changes in 20th-century wildland fire potential and substantiate the relationship of these changes to historic fire frequency. Unlabeled photo pairs depicting historic versus recent vegetation conditions at seven diverse locations in the western U.S. were evaluated by 32 wildland fire professionals. Their ratings demonstrated a large and significant increase in perceived crown fire potential (d [the standardized mean difference between ratings for recent and historic conditions] = 0.83, 95% CI = 0.34 ≤ d ≤ 1.23) and a moderate and significant increase in fire severity potential (d = 0.66, 95% CI = 0.25 ≤ d ≤ 1.04), but no change in spread rate potential (d = –0.29, 95% CI = –0.79 ≤ d ≤ 0.13). Perceived changes in crown fire potential and potential fire severity are both related to the historic fire regime of forested photo locations (P = 0.012 and 0.015, respec­ tively), with the greatest amount of change perceived where fire was historically most frequent. These results support the use of the historic fire regime–current condition class concept to justify and prioritize fuel treatments that reduce the potential for crown fires on forested lands. keywords: fire exclusion, fire hazard, fire regimes, fuel treatments, repeat photography, vegetation change, western U.S. Citation: Martinson, E.J., and P.N. Omi. 2004. Relating historic fire regimes to 20th-century fire potential may augment ecological justifications for expanded fuel treatment programs. Pages 36–42 in R.T. Engstrom, K.E. M. Galley, and W.J. de Groot (eds.). Proceedings of the 22nd Tall Timbers Fire Ecology Conference: Fire in Tem­ perate, Boreal, and Montane Ecosystems. Tall Timbers Research Station, Tallahassee, FL. INTRODUCTION Writings (e.g., Cooper 1960) and photographs (e.g., The severity of recent wildfire seasons (e.g., 1988, Veblen and Lorenz 1991) from the period of Euro­ 1994, 1996, 2000, 2002) in the western U.S. support American settlement anecdotally support suppositions assertions of increased fire potential as a result of of increased fuel accumulation in some ecosystems more hazardous fuel profiles created by fire exclusion since the advent of organized fire suppression in the during the 20th century. This chain of hypotheses is early 20 th century. Gruell et al. (1982) used hazard ratoften invoked to provide ecological justification for ings by a fuels specialist in their repeat photography expanded fuel treatment programs on U.S. federal study to infer a general hazard increase since 1909. We lands (e.g., USDA Forest Service 2000). Fire history took a similar but broader approach to quantify and studies provide widespread graphic evidence that fire differentiate changes in fire potential represented in exclusion during the 20th century has dramatically repeat photographs that have been published for a reduced fire frequency in many ecosystems (Swetnam variety of ecosystems in the western U.S. It is gener­ et al. 1999). Since fire is an agent of mortality (Ryan ally presumed that fire exclusion has had the greatest et al. 1988) and a process of accelerated decomposiimpact on ecosystems that historically experienced a tion (Ottmar et al. 1993), reduced fire frequency regime of frequent fires (Covington and Moore 1994). would be expected to result in greater fire hazard due We tested the hypothesis that the degree of perceivable to increased surface fuel loads, more abundant ladder difference in fire potential represented in repeat pho­ fuels, and denser canopy fuels (Agee 1996). tographs is related to the historic fire frequency at