Downed woody fuel loading dynamics of a large-scale blowdown in northern Minnesota, U.S.A.

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On July 4, 1999, a large-scale blowdown occurred in the Boundary Waters Canoe Area Wilderness (BWCAW) of northern Minnesota affecting up to 150,000 ha of forest. To further understand the relationship between downed woody fuel loading, stand processes, and disturbance effects, this study compares fuel loadings defined by three strata: (1) blowdown areas of the BWCAW (n = 34), (2) non-blowdown areas of the BWCAW (n = 55), and (3) the greater forest ecosystem in which the BWCAW lies (n = 228). Further, relationships between downed woody fuel estimates and standing tree attributes (stand basal area and trees per hectare) were compared among study strata. Results indicate that mean 100 and > 1000 h timelag fuel loadings in blowdown areas of the BWCAW (13.0 and 22.9 tonnes/ha, respectively) were substantially higher than those in both the non-blowdown areas of the BWCAW (5.8 and 16.3 tonnes/ha, respectively) and the greater forest ecosystem (6.5 and 11.3 tonnes/ha, respectively). There was no relationship between fuel loadings and trees per hectare or stand basal area. However, there did appear to be defined limits to maximum observed fuel loadings in relation to stand density attributes. This study suggests that relationships between a forest ecosystem's standing live and downed dead tree attributes are obscured by two contrasting events: widespread mortality from large-scale disturbances and the limited mortality from gradual stand development/small-scale disturbances.

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Forest Ecology and Management