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

Christopher B Oneal,John D Stuart,Steven J Steinberg,Lawrence Fox

doi:10.4996/fireecology.0201073

Christopher B Oneal, John D Stuart + Show 2 more

Open Access

https://doi.org/10.4996/fireecology.0201073

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Abstract

A geographic information system (GIS) was used to analyze the effects of six physical variables (redwood sub-region, slope, aspect, elevation, distance from the coast, and moisture regime) on the natural fire rotation (NFR) of redwood (Sequoia sempervirens) forests between 1950 and 2003. NFR is defined as the years necessary for fires to burn over an area equal to that of the study area. This analysis relied on a spatial database of forest fire locations cataloged by California Department of Forestry and Fire Protection. The NFR for the California range of redwood forests was calculated as 778 years. The NFRs for north, central, and southern redwood sub-regions were 1,083, 717, and 551 years, respectively. The NFR of slope classes varied between 3,309 years for flat terrain and 423 years for steep slopes. The NFRs of north and south aspects were 796 years and 763 years, respectively. Elevation classes of 200 m illustrated a consistent decreasing trend in NFR values, 1,841 in the lowest elevation class and 53 years in the highest. Distance from the coast was classed in 5 km increments up to 50 km with NFR values of 648 years in the 5 km class and 1,148 years in the 50 km class. The NFRs of moisture regime classes were 1,183 years in the wettest class and 117 years for the driest class. Drier moisture regime classes were prevalent in the southern redwood range. The NFR calculated for redwood sub-regions, moisture regimes and elevation classes indicated that periodicity of fire in redwood stands decreased along a north-south, west-east gradient. The NFRs observed in these redwood variables substantiate results from previous work concerning the influence of a north-south, ocean-inland gradient on fire frequency in redwood forests.

Highlights

The time period for this study was encompassed within the suppression era
As a study area increases beyond a certain size, the mean fire interval (MFI) ceases to be an appropriate measure of frequency (Agee 1990) because of its inverse relationship to the sample unit size (Arno and Petersen 1983)
Disproportionate area ratios may result in anomalous natural fire rotation (NFR) values

Summary

Introduction

The time period for this study was encompassed within the suppression era. It is recognized that anthropogenic factors were influential on results reported here; the term “natural” fire rotation should not be interpreted in the strictest sense. Utilization of the term natural fire rotation is in keeping with its conventional use as a fire frequency metric. As a study area increases beyond a certain size, the MFI ceases to be an appropriate measure of frequency (Agee 1990) because of its inverse relationship to the sample unit size (Arno and Petersen 1983). For the 215, 000 ha area comprising the Boundary Waters Canoe area in Minnesota, the natural fire rotation (NFR) was developed as a measure of fire frequency (Heinselman 1973). A large area, the 880,000 ha of California’s redwood (Sequoia sempervirens) forests (Fox and Lee 1989) warrant the use of NFR as a measure of fire periodicity

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Results

Conclusion