Prescribed Mosaic Burning in California Chaparral

In fire-prone ecosystems, knowledge of previous fire history and long-term fire regimes is essential to the establishment of ecologically sound fire management. In the Californian chaparral, fire regimes are determined by the rate of fuel accumulation and previous fire history. The evolution of patch mosaics created by fire is a non-random and self-organizing process because the occurrence of fire events is affected by past events, and in turn affects future events. A strategy that increases the frequency of burns (events/area) on the landscape can reduce the probability of large fires by establishing a highly fragmented patch structure. Baja California's chaparral has a highly fragmented patch structure that is resistant to the spread of large fires. Because it is an example of ecosystems functioning under natural disturbance, it should be used as a model for fire management in California. In fire-prone ecosystems, knowledge of previous fire history and long-term generic fire regimes (fire intervals, intensities, size, weather) is essential in the evaluation of relationships between fire and vegetation dynamics, as well as in the establishment of ecologically sound fire management. In the California chaparral, the fire regime is characterized by a self-organizing patch dynamics, making the vegetation an ideal setting for proactive broadcast planned burning for fuel management. A strategy that increases the frequency of burns (events/ area) on the landscape can reduce the probability of large fires by establishing a high degree of fragmentation in patch structure. These findings emanate from the profound discontinuity in land-use and fire history along the United States-Mexican boundary (Minnich 1983, Minnich and Chou 1997). In the United States, anthropogenic control of fire has been in place for a century, whereas little or no fire control has occurred in the isolated wildlands of northern Baja California. On the Mexican side of the international boundary, the chaparral appears as a diverse, fine-grained patch mosaic. From any view, a dozen patches of different ages may be seen---from fresh burns, to medium-sized stands, to dense old-growth stands. Beneath distant smoke columns are fires creeping through the brush with discontinuous lines of flames less than 5 m in length. North of the international boundary, however, the mountains support unbroken, dense, old-growth chaparral interspersed by a few extensively denuded watersheds from a fire provoked by a past Santa Ana wind. This paper discusses the process by which a superior chaparral landscape has developed in Baja California without fire management. Self-regulating Fire Regime In the Californian chaparral, the fire regime is constrained in time and space by the rate of fuel accumulation and previous fire history (Minnich and Chou 1997). Although the standing biomass is high (40 to 100 tons per hectare), the flammability of stands remains low during the first decades of succession because of low fuel continuity (stand cover) and biomass, as well as high stand fuel moisture due to low dead-to-live stand fuel ratios. Fuels tend to be moist because the evergreen shrubs have good stomatal controls, and evapotranspiration rates are low despite high evaporative demand. This efficient internal water regulation, coupled with low annual biomass production tend to reduce interannual An abbreviated version of this paper was presented at the Symposium on Fire Economics, Planning, and Policy: Bottom Lines, April 5-9, 1999, San