Date of this Version
Joint Fire Science (08-1-5-04) Final Report, Fraver et al.
The patchiness resulting from a sequence of recent disturbances – blowdown, salvage logging, and wildfire – provided an excellent opportunity to assess the impacts of these disturbances, singly and in combination, on (1) wildfire severity (2) post-disturbance vegetation responses, (3) ecosystem carbon stocks, and (4) soil mercury (Hg) accumulation or loss in jack pine (P. banksiana) forests of northern Minnesota. Considering issue 1, our results suggest that salvage logging reduced the intensity (heat released) of the subsequent fire. However, its effect on severity (impact to the system) differed between the tree crowns and forest floor. Considering issue 2, our results suggest that disturbance combinations (blowdown and fire with and without salvage logging) resulted in similar woody plant communities, largely dominated by trembling aspen (Populus tremuloides). By comparison, areas experiencing solely fire were dominated by jack pine regeneration, and areas experiencing solely blowdown were dominated by regeneration from shade-tolerant conifer species. Considering issue 3, our results suggest that various disturbances cause dramatic shifts in the proportion of carbon in different pools, suggesting that potential increases in multiple disturbance events may represent a challenge for sustaining ecosystem carbon stocks. Considering issue 4, our results suggest that when disturbance combinations are considered in addition to singular disturbances, unexpected consequences in atmospheric Hg emission, soil Hg accumulation, and risk to aquatic biota may result. Taken together, these results lend themselves to improved forest management strategies, particularly regarding post-disturbance harvesting prescriptions.
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