PARENT SESSION
Symposium #13: Fire suppression impacts in crown fire ecosystems.
Sponsored by ESA Vegetation Section
Organized by: J. E. Keeley and E. A. Johnson.
Wednesday, August 8, 2001. 8:00 AM to 12:00 PM. Lecture Hall
Spatial variation and age dependency in burning patterns.
MORITZ, MAX1, 1
ABSTRACT- In California's mediterranean-type shrublands, there is debate over whether fire suppression has caused large fires by homogenizing the spatial pattern of fuels (i.e., age classes) on the landscape. This debate can be distilled to the following: Is fire capable of spreading through young vegetation, and do shrubland fire regimes exhibit strong age dependence in burning patterns? To identify the dominant control on disturbance regimes of chaparral-dominated ecosystems, I analyzed the GIS-based fire history (1911-1995) of Los Padres National Forest in central coastal California. In quantifying age dependency, I first identified homogeneous subregions using only fire history-related variables (i.e., average and extreme fire intervals, sizes, seasonality, and causes). I employed iterative statistical clustering of mapped attributes and found six unique subregions; this landscape classification was also validated through regression tree analysis of the same variables. I then generated age-at-burn distributions and estimated parameters for the generalized Weibull function commonly used to assess how the hazard of burning changes with time. None of the shrubland-dominated subregions showed an absence of burning in younger fuels, and all but one subregion exhibited minimal increases in hazard with time since the last fire. The subregion exhibiting a moderate increase in fire hazard probably does so because it is topographically sheltered from extreme fire weather common in most shrubland ecosystems; therefore, this area displays a more fuel-limited dynamic than others. Because extreme fire weather is the dominant control on fire regimes of many chaparral-dominated shrublands, modification of fuel characteristics through fire suppression is not the direct cause of large fire events. This has implications for both the ecology and management of these ecosystems, and it may require consideration in land use planning decisions.
KEY WORDS: California, chaparral, fire, hazard