|Title||Post-Glacial Vegetation of Eastern Upper Michigan|
|Year of Publication||1982|
|Degree||Doctor of Philosophy|
|University||University of Michigan|
|City||Ann Arbor, MI|
The postglacial vegetational history of Chippewa, Luce, and Mackinac counties, Michigan was studied through stratigraphic analysis of fossil pollen in sediments from ten lake and bog sites. This region of ca. 6000 square km is bounded by Lakes Superior, Michigan, and Huron; its surface varies from flat to rolling and is covered by a veneer of sandy glacial drift and lacustrine deposits. A mosaic of hardwood forests, pine forests, and extensive bogs and conifer swamps comprises the present vegetation. The general sequence of events interpreted from the pollen stratigraphies is as follows: 1) Late-glacial and early Holocene forests were dominated by jack pine (Pinus banksiana) and spruce (Picea). 2) Between 8000 and 5000 years ago (Hypsithermal period) the forests were dominated by white pine (Pinus strobus) or mixtures of white pine, jack pine, and red pine (P. resinosa). 3) Starting about 5000 years ago, hardwood trees such as birch (Betula) and sugar maple (Acer saccharum) became more abundant, and dominant in places. Widespread development of bogs and other peatlands began at this time. The warmer and drier climate of the mid-postglacial Hypsithermal period had a marked effect on the vegetation of the region. At that time, the forests were more xeric in nature, being dominated by pines. As the climate became cooler and moister after 5000 yr B.P., the regional water table rose 1-2 meters, causing the inundation of numerous small lake basins and leading to widespread bog development in poorly drained areas. The large magnitude of water table changes in response to changing climate is due to the high permeability of the sandy surficial deposits. It appears that the mid-Holocene climate changed gradually, since the rise in water table is time-transgressive across the region. Initiation of peatland development and lake basin inundation varied, occurring between 7000 and 3000 yr B.P., the timing at each site being dependent on local hydrological conditions.