Downed woody fuel dynamics of mixed-pine forest ecosystems in the eastern Upper Peninsula of Michigan, U.S.A

Background/Question/Methods

Mixed-pine forest ecosystems once dominated large portions of the northern Lake States, including the eastern Upper Peninsula of Michigan.  However, turn-of-the-century logging and slash fires, followed by extended periods of fire suppression has led to the development of alternate community states.  Many of these forest ecosystems once dominated by red pine (Pinus resinosa Ait.), eastern white pine (P. strobus L.), and maintained by frequent low to moderate severity wildfire, are now dominated by dense stands of jack pine (P. banksiana Lamb.) with extremely high fuel loadings.  As ecologists and resource managers work to restore these forest ecosystems, the fuels pose a significant challenge to restoration efforts.  In order to better understand the relationships between downed woody fuels and past forest management activities, we examined fuel loadings of mixed-pine forest ecosystems at the Seney National Wildlife Refuge (SNWR).  Specifically, we compared fuel loadings of stands that have experienced: 1) harvesting only (n=13), 2) harvesting followed by prescribed fire (n=24), 3) harvesting followed by natural fire (n=6), and 4) no harvesting and little modification of the natural fire regime (reference; n=37).  Downed woody fuels were collected using standard methodologies developed by the Forest Inventory and Analysis (FIA) of the U.S.D.A. Forest Service.

Results/Conclusions

Our results indicate low levels of large fuels (>1,000 hr fuels) among the different disturbance classes.  However, fine woody debris (FWD; 1 hr, 10 hr, and 100 hr fuels) was highly variable and different among the four disturbance classes.  Specifically, stands that have experienced harvesting followed with natural fire have on average (+/- 1SD) the lowest FWD loadings 171.1 (+/- 94.7) tonnes/ha while those harvested stands followed with prescribed fire have the highest FWD loadings 407.4 (+/- 200.8) tonnes/ha.  The FWD loadings in the harvested only stands and the reference stands were similar, 283.2 (+/- 126.0) and 320.2 (+/-139.5) tonnes/ha respectively.  These results suggest that the influence of past disturbance on fuel loadings in mixed-pine forest ecosystems is highly variable.  We surmise that this variability may be related to the intensity of past disturbances and resulting stand structures.  Future analyses will attempt to account for these differences in an effort to elucidate the legacies of past disturbance on fuel loadings in these mixed-pine forest ecosystems.