5th Symposium on Fire and Forest Meteorology and the 2nd International Wildland Fire Ecology and Fire Management Congress

Wednesday, 19 November 2003: 4:30 PM
Fire effects on forest spatial patterns in the Arizona sky islands
Mary C. Henry, Miami University, Oxford, OH
Aggressive fire suppression and livestock grazing in Western forests during the 20th century has lead to increased fuel loads, as well as changes in forest age structure and species composition. Many forest ecosystems that historically experienced low intensity surface fires (including Ponderosa pine) are now prone to high intensity crown fires with high mortality rates among mature trees. Fire effects are spatially complex, driven in part by the amount and connectivity of fuels present. These spatial variations in turn impact future fires. Satellite-based remote sensing offers a synoptic view of the landscape and allows quantitative analysis of landscape patterns over time.

This research uses Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus(ETM+) image data to assess changes to forest landscape patterns following a 1994 fire in the Rincon Mountains of southeastern Arizona. Digital orthophotos (DOQQs) acquired after the fire show a wide range of mortality rates, which appear linked to fire history prior to the 1994 fire. Previous work by the author, using single-date TM data showed significant relationships between fire history (i.e., fire frequency) and landscape patterns (e.g., fractal dimension, patch size, patch size variability).

The current study will assess and quantify landscape pattern changes in areas with differing fire histories and monitor those patterns for several years following the fire. Six study sites (used in previous research) were selected with a range of fire histories (one to six fires between 1943 and 1994) and varying levels of fire damage. Landscape patterns will be calculated from image enhancements, including the tasseled cap transform and normalized difference vegetation index (NDVI). Image segmentation (object-oriented image analysis) will be used to create patch maps from each image enhancement and landscape metrics will be calculated for each date. It is expected that fire-excluded areas will show decreases in landscape heterogeneity following the 1994 fire (as a result of widespread tree mortality), while frequently burned areas will exhibit fewer changes in landscape pattern.

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