Landscape-level control of population dynamics: late-Quaternary paleoecology of beech in upper Michigan

In this study I investigated the role lake-effect climate, soil type, and topography played in the late-Quaternary establishment, expansion, and decline of American beech in eastern Upper Michigan. General Land Office surveys and modem soil surveys were used to establish the presettlement distribution of beech on nine soil cover types in an eight township study area in Mackinac County, Michigan. Pollen analysis from small lakes (<10 ha) varying in distance from Lake Michigan (2-15 km) and surrounded by various soil types were used to determine the establishment, expansion, and decline of American beech.

Presettlement beech was positively associated with loamy soils over gravelly till, sandy soils with ortstein, and loamy, sandy soils over gravelly till. An outlying population of beech became established 5790 yr BP near the climatically ameliorated shore of Lake Michigan on fine-textured loamy soils. At a second site also surrounded by fine-textured loamy soils beech pollen did not reach appreciable levels until 5070 yr BP. Between 3000 and 2500 yr BP beech populations increased throughout Upper Michigan at sites on loamy soils, and expanded onto the areally more abundant sandy soils with ortstein.

These results indicate that climate amelioration by Lake Michigan and fine-textured soils were both required for beech establishment at 5790 yr BP in eastern Upper Michigan. Expansion of beech populations around 3000 yr BP onto coarse-textured soils was most likely the result of soil development at the landscape level and a shift to a more mesic climate regionally. Since 2000 yr BP, selected populations of American beech declined in response to habitat loss as lowland mesic sites became more hydric in response to paludification. Other populations collapsed as upland mesic sites became more xeric in response to lowering of water tables due to isostatic rebound and river downcutting. The occurrence of an outlying population of American beech along the ameliorated shores of Lake Michigan during the Hypsithermal interval provides a partial analog for potential refugia under an enhanced Greenhouse climate.