Fire-dependent mixed-pine forest ecosystems once dominated large portions of the northern Lake States. In the late 1800s and early 1900s, these ecosystems were significantly altered by extensive logging, wildfires, and fire suppression. The legacies of these disturbances have been an accumulation of fuels outside of the natural range of variation, decline in the establishment of both red pine (Pinus resinosa Ait) and eastern white pine (P. strobus L.) and increase in the dominance of jack pine (P. banksiana Lamb). Recently, efforts across the region have begun to focus more on restoring mixed-pine forests ecosystems. However, before specific recommendations on how to restore these forest ecosystems can be developed, it is important to understand how both natural and human disturbances have influenced regeneration-layer dynamics. In this study, we compared the regeneration layer composition and structure among four land management types (harvest+prescribed fire, harvest+natural fire, harvest, and reference conditions) nested within two landform types (sand ridges and outwash channels) at the Seney National Wildlife Refuge in eastern Upper Michigan. Specifically, we inventoried all seedlings (stems < 2.5 cm dbh) by species and related these data to overstory composition and structure, canopy closure, and fuel loadings.
Results/Conclusions
Total seedling density ranged from a mean of 262 seedlings ha-1 in the harvest only stands to 606 seedlings ha-1 in the reference stands, with red pine and eastern white pine densities being greater in the harvest+prescribed fire and the reference conditions than the harvest+natural fire and harvest only management types. Overall, the composition of the regeneration layer was different among the different land management types (Multi-response Permutation Procedure P=0.003). Furthermore, canonical correspondence analysis suggests that the observed differences in regeneration layer composition are primarily associated with differences in fuel loading characteristics and land-use history. For example, seedling densities of species relatively intolerant of fire (including red maple (Acer rubrum L.)) were found to dominate areas with harvesting+prescribed fire, while seedling densities of red and eastern white pine were higher in the reference areas where the fire regime is believed to be relatively intact. These results, in conjunction with planned experimental studies of regeneration layer response to specific silvicultural and restoration treatments will help refine models of forest development, improve strategies that enhance red and white pine establishment, and ultimately help restore these once-extensive forest ecosystems.
