REU: Long-Term Processes Affecting the Hemlock-Hardwood Mosaic at Sylvania, Michigan

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Processes responsible for the mosaic of hemlock stands and hardwood stands in the old-growth forest at Sylvania, Michigan will be studied with retrospective techniques. These approaches include reconstruction of disturbance history over the last two centuries from tree-rings, windstorms, fire and the consequent changes in forest composition over the last five millennia from pollen deposits in small forest hollows. The mosaic of stands and soil textures will be studied in three permanent plots established on different soil types. The ways in which the mosaic changed through time in response to climatic change, to changes in disturbance regimes and to the invasion of hemlock beginning three thousand years ago, will be monitored by pollen diagrams from closely spaced spatial arrays of hollows, approximately one per hectare, within each of the plots. Mosaic changes on a large spatial scale will be shown in pollen diagrams from seven additional hollows scattered throughout Sylvania in stand types not represented in the plots. Modeling and studies of pollen representation will develop needed techniques for accurate interpretation of pollen assemblages from heterogeneous vegetation.