Geographic analysis of natural fire rotation in the California Redwood Forest during the suppression era

Abstract

A geographic information system (GIS) was used to analyze the effects of six physical\rvariables (redwood sub-region, slope, aspect, elevation, distance from the coast, and\rmoisture regime) on the natural fire rotation (NFR) of redwood (Sequoia sempervirens)\rforests between 1950 and 2003. NFR is defined as the years necessary for fires to burn\rover an area equal to that of the study area. This analysis relied on a spatial database of\rforest fire locations cataloged by California Department of Forestry and Fire Protection.\rThe NFR for the California range of redwood forests was calculated as 778 years. The\rNFRs for north, central, and southern redwood sub-regions were 1,083, 717, and 551\ryears, respectively. The NFR of slope classes varied between 3,309 years for flat terrain\rand 423 years for steep slopes. The NFRs of north and south aspects were 796 years and\r763 years, respectively. Elevation classes of 200 m illustrated a consistent decreasing\rtrend in NFR values, 1,841 in the lowest elevation class and 53 years in the highest.\rDistance from the coast was classed in 5 km increments up to 50 km with NFR values of\r648 years in the 5 km class and 1,148 years in the 50 km class. The NFRs of moisture\rregime classes were 1,183 years in the wettest class and 117 years for the driest class.\rDrier moisture regime classes were prevalent in the southern redwood range. The NFR\rcalculated for redwood sub-regions, moisture regimes and elevation classes indicated that\rperiodicity of fire in redwood stands decreased along a north-south, west-east gradient.\rThe NFRs observed in these redwood variables substantiate results from previous work\rconcerning the influence of a north-south, ocean-inland gradient on fire frequency in\rredwood forests.