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Ponderosa Pine Fire History in the Southwest (adapted from Cram et al. 2006) Southwestern forests, particularly those dominated by ponderosa pine (Pinus ponderosa), developed under the influence of frequent fire (Sackett and others 1993). Reported mean fire intervals for southwestern ponderosa pine forests range between two to 12 years (Weaver 1951; Cooper 1960; Dieterich 1980). Over the last 10,000 years, frequent fire shaped vegetation composition, stand development, and structure in pine-grassland communities (Weaver 1943, 1964, 1967; Biswell 1959, 1972; Cooper 1960, 1961; Pyne 1982; Covington and Moore 1994). Frequent fires, characterized as light to moderately severe, were largely understory fires and killed few overstory pines. Fire acted as a natural thinning agent by reducing litter build-up, burning small trees, and thinning ladder fuels. Resulting forests were open and park-like with invigorated herbaceous understories providing the surface fuel for the fire cycle to repeat itself (Ahlgren and Ahlgren 1960; Moir and others 1997). Due to their open nature and lack of ladder fuels, stand replacement fires were historically uncommon in southwestern ponderosa pine forests (Woolsey 1911; Cooper 1960; Pyne 1996). However, a number of factors combined to change forest structure, understory and overstory composition, fuel biomass conditions, and the historic natural fire regime in southwestern forests over the last 120 years. Early contributing factors around the turn of the 20th century included logging practices (Habeck 1990) that removed overstory trees allowing for prolific conifer regeneration (Cooper 1960; Schubert 1974) and heavy grazing by sheep and cattle, which removed fine surface fuels necessary for fire spread (Baker and others 2004). Moreover, throughout the last 90 years fire suppression efforts and exclusion policies contributed significantly to extreme biomass fuel buildup as well as other ecological changes in these forests. Although early ecologists opposed to the 10 a.m. policy (the 10 a.m. policy was introduced and adhered to by the U.S. Forest Service in 1935; the policy stipulated a reported fire was to be contained by 10 a.m. the following day, and failing that, controlled by 10 a.m. the next day, and so on) and later others such as H. Weaver (1943) warned of increasing fire danger based on increasing biomass fuel loads due to lack of frequent surface fire, little attention was heeded. As a result, high-intensity crownfires have replaced low-intensity fires in southwestern pine-grassland stands threatening not only those communities at the wildland-urban interface, but also the ecological integrity of vast areas throughout the West. Literature Cited Ahlgren, I.F.; Ahlgren, C.E. 1960. Ecological effects of forest fires. Botanical Review 26:483–533. Baker, M.B., Jr.; Ffolliott, P.F.; DeBano, L.F.; Neary, D.G. 2004. Riparian areas of the southwestern United States–hydrology, ecology, and management. Boca Raton, FL: CRC Press. 408 p. Biswell, H.H. 1959. Man and fire in ponderosa pine in the Sierra Nevada of California. Sierra Club Bulletin. 44:44–53. Biswell, H.H. 1972. Fire ecology in ponderosa pine-grassland. In proceedings of the 12th Annual Tall Timbers Fire Ecology Conference, Lubbock, TX. 12:69–96. Cooper, C.F. 1960. Changes in vegetation, structure, and growth of southwestern pine forest since white settlement. Ecological Monographs 30:129–164. Cooper, C.F. 1961. Patterns in ponderosa pine forests. Ecology 42:493–499. Covington, W.W.; Moore, M.M. 1994. Southwestern ponderosa forest structure: changes since Euro American settlement. Journal of Forestry 92:39–47. Cram, D.S.; Baker, T.T.; Boren, J.C. 2006. Wildland fire effects in silviculturally treated vs. untreated stands of New Mexico and Arizona. Research Paper RMRS-RP-55. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Paper. 28 p. Dieterich, J.M. 1980. Chimney Spring forest fire history. Res. Pap. RM-220. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 8 p. Habeck, J.R. 1990. Old-growth ponderosa pine-western larch forest in western Montana: ecology and management. The Northwest Environmental Journal 6:271–292. Moir, W.H.; Geils, B.; Benoit, M.A.; Scurlock, D. 1997. Ecology of southwestern ponderosa pine forests. In: Block, W.M.; Finch, D.M. technical editors. Songbird ecology in southwestern ponderosa pine forests: a literature review. Gen. Tech. Rep. RM-GTR-292. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 3–27. Pyne, S.J.; Andrews, P.L.; Laven, R.D. 1996. Introduction to wildland fire. New York: John Wiley and Sons. 769 p. Sackett, S.; Haase, S.; Harrington, M.G. 1993. Restoration of southwestern ponderosa pine ecosystems with fire. In: Covington, W.W.; DeBano, L.F. technical coordinators. Sustainable ecological systems: implementing an ecological approach to land management. Gen. Tech. Rep. RM-247. Fort Collins, CO: U.S. Department of Agriculture Forest Service, Rocky Mountain Forest and Range Experiment Station: 115–121. Schubert, G.H. 1974. Silviculture of southwestern ponderosa pine: the status of our knowledge. Res.Pap. RM-RP-123. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 71 p. Weaver, H. 1943. Fire as an ecological and silvicultural factor in the ponderosa pine region of the Pacific slope. Journal of Forestry 41:7–15. Weaver, H. 1951. Fire as an ecological factor in the southwestern ponderosa pine forests. Journal of Forestry 49:93–98. Weaver, H. 1964. Fire and management problems in ponderosa pine. In proceedings of the 3rd Annual Tall Timbers Fire Ecology Conference, Tallahassee, FL. 3:61–79. Weaver, H. 1967. Fire and its relationship to ponderosa pine. In proceedings of the 7th Annual Tall Timbers Fire Ecology Conference, Tallahassee, FL. 7:127–149. Woolsey, T.S. 1911. Western yellow pine in Arizona and New Mexico. Bulletin 101. U.S. Department of Agriculture, Forest Service. |