Pollen Spectra from Four Bogs on the Gillen Nature Reserve, Along the Michigan-Wisconsin State Line

Abstract

Northern Wisconsin impresses a visitor from central Indiana not only with its decided differences in climate but also by the change in the vegetation, the visible expression of the climate. This is, perhaps, less evident to-day than formerly because the vast forests of conifers which a half century ago covered much of the topography have under pressure of lumbering and fire yielded to scrubby growth of aspen and paper birch, or perhaps even to lowly shrubs of the heath family, and especially to Comptonia asplenifolium. There are, however, in Vilas county, Wisconsin, and Gogebic county, Michigan, smaller areas of hardwoods and pine still in their natural, undisturbed condition, where phytosociology is representative of the former greater forest expanses of the region before cultural influences modified them. Here, then, was an unusual opportunity to make a pollen study in bog sediments, and fit pollen records into a vegetation complex of to-day, and thus bring the study of the vegetaional tendencies in the region up to the present. Four bogs were included in the study. They are located near the Michigan-Wisconsin state line, on the Gillen Nature Reserve. This reserve is a fine 5,500 acre tract lying partly in Vilas county, Wisconsin, and partly in Gogebic county, Michigan. In its geographical location it is close to the Canadian forest, and character species of the boreal forest are prominent dominants in this southern extension, in relic colonies in bogs and along wet river bottoms. The vegetation as a whole is of the true lake forest type, i.e., pine dominating in sandy, dry areas, and northern hardwoods of yellow birch (Betula lutea), hemlock (Tsuga canadensis), and sugar maple (Acer saccharum) dominating in forests on better loam soils. Beech (Fagus grandifolia) has not extended its range so far west. The northern hardwoods was originally very prominent in the area now termed the Gillen Nature Reserve, and pine had a rather scattered distribution. From pollen profiles of Indiana bogs and lakes we were justified to conclude that the broadleaved phase of the lake forest complex is a more recent invasion than the pine complex, and as stated before, bogs in the Gillen Nature Reserve appeared to be excellently located to fit pollen spectra into representatives of forest primeval still surrounding some of the bogs studied. Here also was an opportunity to check the reliability of pollen spectra in recording forest complexes and forest changes, and to discover when the hardwoods complex first replaced in part the pine dominance. In compliance with the wishes of Mr. Martin J. Gillen, former owner of the reserve, the three deeper bogs were named in recognition of