Analyzing fire mosaics in temperate coniferous forests with GIS and remote sensing

This investigation on fire mosaics addressed several aspects:(1) quantifying the role of terrain variables in fire-relatedmortality and historical mean fire return interval (MFRI), (2)comparing post-burn Landsat Thematic Mapper (TM) imagery, TMdifference imagery, and aerial photo interpretation to map forestsurvival after wildfire, and (3) to describe and discuss wildfireeffects on successional stage patterns and wildlife habitat.
The two study sites were located on the Willamette NationalForest in the Oregon Cascades. The Warner Creek burn was the locationof a 1991 wildfire covering 3669 ha; the Upper McKenzie site was thelocation of ecological and historical fire studies.
Historical MFRI, terrain, and vegetation data were input into ageographical information system. Random sampling was conducted on alllayers, and was also used to ground truth forest survival, primarilywith aerial photography. Relationships of terrain to forest survivaland historical MFRI were analyzed with regression. Regression wasalso used to model forest survival with TM data. Error matrices wereused to compare classified TM data and aerial photo interpretation inmapping survival.
At both sites, terrain variables accounted for more variation inforest survival (12-62%) or historical MFRI (4.8-21.9%) withinindividual physiographic areas, than across the respective studyareas. Moreover, the significant topographic variables differed amongindividual physiographic areas.
Regressions of TM band transformations were used to evaluateforest survival. The TM difference imagery with stratification bypre-fire tasseled cap (TC) wetness explained 75% of the variation inlive canopy ratio, and post-burn TM Structural Index (SI) accountedfor 72%. Classification of the TM difference imagery with pre-fire TCwetness had an overall accuracy of 68%, that of the post-burn SI was63%, and that from aerial photo interpretation was 56%.
Before the burn, landscape matrix was closed mature/old-growth.After the burn, the early seral/rock stage expanded, the openmature/old-growth stage was created, and the closed mature/old-growthwas reduced and fragmented. Thus, overall habitat diversity and edgeincreased, but interior habitat decreased. Also, patches of earlyseral/rock were more variable in size and complex in shape thanstaggered setting clearcuts on public lands.