Appendix A. Site information and field methods.
Pinhook Bog is located in LaPorte County in northwestern Indiana (41°36'53.72"N, 86°50'48.25"W; ~245 m above sea level), approximately 12 km southwest of Lake Michigan (44) (Fig. A1). The peatland occupies a 40-ha kettle-hole depression on the Valparaiso moraine, and is effectively isolated from the regional hydrology by the sandy-clay glacial till (Wilcox and Simonin 1988, Futyma 1988). Most of the peatland is floating on a trapped water pocket, except near the edges. Pollen was previously studied from a sediment core collected near the center of the peatland, but sample density from the last 2000 years was low (Futyma 1988). Vegetation of the peatland includes Sphagnum mosses, Drosera intermedia (spoonleaf sundew), Sarracenia purpurea (purple pitcher plant), Vaccinium oxycoccus (cranberry), Chamaedaphne calyculata (leatherleaf), Vaccinium corymbosum (highbush blueberry), and Larix laricina (tamarack). The vegetation of the surrounding upland is composed of Quercus-dominated mixed hardwood forest that includes Fagus grandifolia, Acer saccharum (sugar maple), Carya spp. (hickory), and Fraxinus spp. (ash).
South Rhody Bog (46°33'53.40"N 86°4'27.91"W; ~285 m above sea level) is a ~4.5 ha kettle peatland located in central Upper Michigan about 12 km south of Lake Superior (Fig. S1). Sandy outwash and moraine deposits characterize the region, and the upland forest surrounding the peatland is dominated by Pinus strobus, Acer saccharum, Fagus grandifolia, Tsuga canadensis, Betula allegheniensis, and Picea mariana. Vegetation of the peatland is dominated by Sphagnum spp., Carex oligosperma, C. limosa, Chamaedaphne calyculata, and Vaccinium oxycoccos. More details on vegetation, water chemistry, and the paleoecological record of South Rhody Bog can be found elsewhere (Booth et al. 2004).
Irwin Smith Bog, located in Alpena County, MI about 13 km west of Lake Huron (45° 1'51.02"N, 83°37'1.43"W, 223 m above sea level) is presently ~65 ha in size and may have been larger before agricultural development of the surrounding landscape. Peatland vegetation is dominated by Sphagnum mosses, a variety of low-growing ericaceous shrubs (e.g., Kalmia polifolia, Chamaedaphne calyculata), and scattered trees (e.g., Larix laricina, Picea mariana, Pinus strobus). Much of surrounding Alpena County is currently used for agriculture, although pre-settlement vegetation was a mosaic of conifer swamp and upland areas dominated by forests of mixed Pinus strobus – Pinus resinosa, Pinus strobus and mixed hardwoods, and hardwood forests dominated by Acer saccharum, Tsuga canadensis, and Fagus grandifolia (Comer et al. 1995).
Minden Bog is an ombrotrophic peatland located in Sanilac County, MI (43°36'32.78"N 82°50'5.25"W, ~ 240 m above sea level) about 20 km east of Lake Huron. Vegetation of the bog is dominated by Sphagnum mosses, low-growing shrubs (e.g., Chamaedaphne calyculata, Kalmia polifolia), and widely scattered trees (e.g., Larix laricina). The surrounding upland is extensively used for agriculture, but the pre-settlement vegetation was a mixture of forests dominated by Acer saccharum, Tsuga candensis, Fagus grandifolia, and Pinus strobus. Additional information on the vegetation, topography, and water chemistry of Minden Bog can be found elsewhere (Booth and Jackson 2003).
Cores were collected from near the center of Minden, Irwin Smith, and South Rhody peatlands with a wide-diameter piston core. At Pinhook Bog a core was collected approximately 20 meters from the peatland margin. This location was chosen to maximize the hydrological sensitivity of the record, because the central portion of this peatland floats on a trapped water pocket, reducing sensitivity (Booth 2010). Cores were carefully wrapped in plastic, aluminium foil, and transported to the laboratory in PVC tubes.
FIG. A1. Location of the four peatland sites in the western Great Lakes region and the average winter precipitation (October-March, 1971–2000) of the region, highlighting the general distribution of the lake-effect precipitation south and east of Lakes Superior and Michigan, much of which comes as snow. Winter precipitation totals at the four sites are as follows: Pinhook, 42.5 cm; South Rhody, 35.6 cm; Irwin Smith, 29.4 cm; Minden, 31.8 cm. Data source: PRISM group, http://www.prism.oregonstate.edu.
Booth, R.K. 2010. Testing the climate sensitivity of peat-based paleoclimate reconstructions in mid-continental North America. Quaternary Science Reviews 29:720–731.
Booth, R.K., and S.T. Jackson. 2003. A high-resolution record of late Holocene moisture variability from a Michigan raised bog. The Holocene 13:865–878.
Booth, R.K., S.T. Jackson, and C.E.D. Gray. 2004. Paleoecology and high-resolution paleohydrology of a kettle peatland in Upper Michigan . Quaternary Research 61:1–13.
Comer, P.J., D.A. Albert, H.A. Wells, B.L. Hart, J.B. Raab, D.L. Price, D.M. Kashian, R.A. Corner, D.W. Schuen, M.B. Austin, T.R. Leibfreid, K.M. Korroch, L. Prange-Gregory, J.G. Spitzley, C.J. DeLain, L.J. Scrimger. 1995. Michigan’s presettlement vegetation, as interpreted from the General Land Office Surveys 1816–1856. Lansing, MI: Michigan Natural Features Inventory. 78 p. + digital map.
Futyma, R.P. 1988. Fossil pollen and charcoal analysis in wetland development studies at Indiana Dunes National Lakeshore. In Interdisciplinary Approaches to Freshwater Wetlands Research (Michigan State University Press).
Wilcox D.A., and H.A. Simonin. 1988. The stratigraphy and development of a floating peatland, Pinhook Bog, Indiana. Wetlands 8:75–91.