Under a warming climate, the Boundary Waters Canoe Area Wilderness (BWCAW) of Northern MN is expected to see an increase in the frequency of disturbances including wildfires and severe windstorms. While boreal forests such as those of the BWCAW are generally considered disturbance adapted, it is uncertain how changing disturbance regimes will impact these forests. We used a series of recent disturbances in the BWCAW ranging from areas affected by wind or fire only, to areas affected by wind followed by fire, or multiple fires, to examine how predicted changes in boreal disturbance regimes are likely to impact these forests. We found that multiple disturbances typically had greater cumulative disturbance severity than single disturbance events and in the case of wind+fire combinations also tended to burn with greater intensity, and fire severity relative to areas affected by a single fire only. While diversity-severity relationships varied in shape, we found that diversity was generally lower at high disturbance severity relative to moderate severities. Multiple disturbances had modestly reduced diversity relative to single disturbances, but this relationship varied depending on the spatial scale of inquiry. Despite only modest impacts on diversity, multiple disturbances did have a pronounced impact on succession and composition. Regardless of pre-disturbance composition, multiple disturbances resulted in succession to aspen and paper birch, with birch being more dominant in areas burned in late season fires and aspen more dominant in areas burned by early season fires. Stands subjected to single disturbance events exhibited multiple successional pathways and mix of forest types. Our results suggest that predicted changes in boreal disturbance regimes are likely to have minor impacts on woody plant diversity, but could adversely affect disturbance adverse species, and alter the age structure and composition of forests by reducing long-lived boreal conifers and increasing the dominance of aspen and paper birch.
University of Minnesota Ph.D. dissertation. January 2018. Major: Natural Resources Science and Management. Advisors: Lee Frelich, Peter Reich. 1 computer file (PDF); x, 201 pages.
Impacts of multiple fires and wind disturbance on forest community composition, succession and diversity in the Boundary Waters Canoe Area Wilderness..
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