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Suppression, fire behavior, and fire magnitudes in Californian chaparral at the urban/wildland interface
| Author: |
Minnich, R.A. and R.J. Dezzani |
| Date: |
1991 |
| Periodical: |
Report No. 75. Berkeley, CA: University of California, Water Resources Center |
| Abstract: |
After nearly a century of suppression, there has been increasing debate that fire control efforts have altered chaparral fire regimes in ways that magnify the threat of burning, erosion, sedimentation and flooding.at the urban/wildland interface (e.g., Pyne 1982). To reverse this trend, there have been efforts to reintroduce fire into the chaparral ecosystem with planned burns. Such a shift in fire management practices, however, will require the understanding of suppression impacts in relation to the character of uncontrolled fire regimes which shaped the chaparral ecosystem. Unfortunately, there are no chaparral areas in California in which suppression is not practiced because suppression is a long-standing policy, thus precluding comparisons against uncontrolled fire. However, chaparral fire regimes in southern California can be compared with uncontrolled fire in adjacent Mexico. The Peninsular Ranges extending from southern California to latitude 30 in northern Baja California, Mexico, share a remarkably uniform geologic substrate, topography, climate and flora that includes widespread stands of chaparral (Minnich and Howard 1984). For the past 100 years, fire regimes in ecosystems to the north and south have diverged. The extension of these mountains into two cultures has created a natural experiment: Fire suppression policy similar to that on the southern California side has not been government policy in Mexico until the 1960s. It is still not effectively practiced there. In southern California, despite limited financial resources, the encirclement of fires, fuel break construction, and other activities of forest rangers beginning in 1900 was followed by a change toward large magnitude fires as early as 1920 (Minnich 19876). The history of fire in chaparral of southern California (SCFA) and adjacent Mexico (BCFA) over the past 60 years, as reconstructed from aerial photographs and Landsat imagery (Minnich 1983, 1989a), reveals a counter-intuitive finding. Fires under suppression in SCFA are larger and more intense than in BCFA, but with little difference in fire return intervals. Clearly, factors other than fuel build-up must be coming into play to explain the present trend of high fire magnitudes in SCFA chaparral. In this paper, we address two topics: 1) the turnover of the chaparral mosaic, and 2) how relationships between suppression, weather and fire behavior are affected by the simple, but efficient process of extinguishing small fires. I then draw a few conclusions on watershed management. |
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