DIFFERENTIATING BETWEEN REGIONAL PALEOCLIMATE, LAKE-EFFECT CLIMATE, AND EDAPHIC FACTORS WHEN INTERPRETING THE LATE HOLOCENE POLLEN RECORDS OF FOUR LAKES IN LOWER MICHIGAN, USA

The Lower Peninsula of Michigan today is characterized by a diversity of plant communities, each responding to multiple environmental controls to varying degrees. The regional climate’s influence is exhibited by an ecotone between the deciduous broadleaf forest and the northern hardwood forest running east-west across the center of this peninsula. Also, areas downwind of the Great Lakes (up to ~80 km) experience a moister and cooler lake-effect climate, compared to inland locations. Moreover, local soil textures vary spatially supporting different vegetation. Therefore, we considered the relative influences of all three factors when interpreting the pollen records of four lakes in Lower Michigan spanning the last 2000 years.

We studied Miner Lake (42.7°N, 85.8°W, Allegan County, 32 km east of Lake Michigan), Duck Lake (42.4°N, 84.8°W, Calhoun County, 107 km east of Lake Michigan), Otter Lake (43.2°N, 83.4°W, Lapeer County, 77 km west of Lake Huron), and Silver Lake (45.2°N, 84.6°W, Cheybogan County, 28-70 km from Lakes Michigan and Huron). The paleovegetation of these four sites changed little over the last 2000 years, with the most notable changes being Euro-American deforestation and before that a taxonomic signal for slightly cooler temperatures during the Little Ice Age (550 to 150 cal yr BP). Miner, Duck and Otter Lakes, all positioned south of the ecotone, were surrounded by Fagus (beech)-Acer (sugar maple) forest on fine-grained soils, with smaller patches of Quercus (oak) vegetation in sandier areas. Interestingly, the Miner record reported a strong lake-effect climate signal, evidenced by pollen abundance of Ulmus (elm) and other wetland taxa when local soils are predominately (82%) coarse grained. The Otter Lake record contained greater abundance of Pinus, Cupressaceae (inferred as Thuja, white cedar) and Larix, reflecting its location closer to the ecotone. Silver Lake, situated within a northern hardwoods forest, was strongly influenced by all three factors over the last 2000 years. During this time, the mesic-hydric white cedar dominated the local flora, with a notable pollen increase from 32 to 73% during the Little Ice Age. In summary, lake-effect climate and local soil characteristics need to be accounted for when interpreting regional climate patterns from pollen records in Lower Michigan.