Fine-scale heterogeneity in overstory composition contributes to heterogeneity of wildfire severity in southern boreal forest |
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Authors: | Daren J Carlson Peter B Reich Lee E Frelich |
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Institution: | (1) Department of Forest Resources, University of Minnesota, 1530 Cleveland Ave. N., 115 Green Hall, St. Paul, MN 55108-6112, USA |
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Abstract: | Wildfire can create a mosaic of impacts of varying severity across the landscape. Although widely recognized, this feature
and its causes are little understood or studied in ecology. We studied a 1,200-ha wildfire in the southern boreal forest of
the Boundary Waters Canoe Area Wilderness (BWCAW) in northeastern Minnesota, USA, using 275 ground plots (stand-scale) and
1:7,000 scale aerial photographs for the entire burned area (landscape-scale). Fire severity was markedly heterogeneous. Overall,
50% of the burn extent was classified as high burn severity, but patches burned this severely were on average less than 70 m
from patches of low severity. As expected, lowlands had lower average fire severity than uplands, but several lowland areas
burned, and some upland areas remained unburned. At the landscape scale, pre-fire vegetation type—itself heterogeneous—and
patch size of less flammable cover types influenced fire severity. Crown fire severity in upland areas was lowest in pure
aspen–birch and red/white pine stands and highest in jack pine and spruce–fir stands. At the stand-scale, slope position and
the density of certain tree species at adjacent plots influenced fire severity. Improved understanding of the severity patterns
created by wildfire can help to guide the management of spatial patterns of forested systems. Based on our study, a larger
range in disturbance severity at scales of 0.1 to several ha and increasing the average size, and range of sizes, of residual
patches would in aggregate better mimic natural disturbance than typical harvests. |
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