Long-term forest dynamics in the hemlock-hardwood forest mosaic of the USFS Sylvania Wilderness Area, northern Michigan, will be studies using fossil pollen in small forest hollows. Histories of individual forest stands, recorded in the sediment, will identify successional communities in the fire-dominated forest ecosystem before hemlock invasion 3000 years ago, making it possible to see whether disturbances made some areas particularly invasible, thus influencing hemlock entry and the locations of hemlock patches that have occupied those sites ever since. By dating hemlock arrival at a series of sites in extreme environments, near bogs or lakes or on coarse soils, we will test the alternative hypothesis that differences in the physical environment were responsible for the locations of hemlock patches. Fine-scale analyses of sediment and time-series analyses of the resulting data will explore changes in successional pathways as the disturbance regime changed from fire to wind 3000 years ago. Modeling will be used to investigate the dynamic changes that have occurred in the positions of boundaries between stands in the forest mosaic. The results will be useful for demonstrating the response of forest communities to climate, including changes in disturbance regimes which may accompany Global Warming. Understanding the origin of the mosaic pattern of forest communities on the landscape may help forest mangers to preserve this aspect of the biodiversity of old-growth forest stands.
