Forest distribution and site quality in southern Lower Michigan, USA.

MICHIGAN; UNITED States

The primary objectives of this research were to determine whether current forest patches in southern Lower Michigan are a proportionate sample of forest types present in the pre-settlement cover and, if not, to establish the degree to which certain types are over- or under-represented in the contemporary landscape. This determination is useful not only because any conservation policy designed to restore the present forest to pre-settlement biodiversity through preservation of existing stands requires an accurate understanding of the degree to which these stands in sum mirror past forest diversity, but also because it fills a gap in the existing ecological literature. The research was conducted within four counties in southern Lower Michigan, USA (Ionia, Livingston, Tuscola and Van Buren). Soil survey data were used to characterize the range of site quality across the study area and the areal extent of each quality category. The geographic locations of all current forest patches in each county were then determined from land use maps and were overlaid on the site quality classification. This procedure yielded the observed distribution of forest relative to site quality. The expected areal extent of forest within each category of site quality on the landscape was determined by assuming a random distribution and multiplying the total area of forestland by the proportion of landscape within each category of site quality. This procedure calculated the expected distribution of forest in terms of site quality by dividing the total forestland among the landscape types, relative to how well represented the landscape types were. The observed and expected distributions were then compared both in terms of absolute difference and normalized difference. Overall results indicate that categories of site quality that support a large proportion of the present-day forest patches are generally composed of agriculturally inferior soil and are over-represented with forest. Surviving or reforested tracts are concentrated on inferior types of habitat. Results suggest that the present-day forest patches may not be a proportionate sample of the primeval forest. Rather, they are concentrated on agriculturally-inferior (coarse-textured, steeply-sloped, or poorly-drained) types of habitat. Unless these stands are for some unknown reason compositionally richer than their pre-settlement counterparts, these results suggest that the existing forest resource in southern Lower Michigan is an inferior (biased) sample of the primeval cover. Furthermore, because forest types associated with the most heavily-developed agricultural sites have apparently suffered the most loss of habitat, species more characteristic of these types may have experienced a greater decline in overall importance across the landscape. This study suggests that policy aimed at increasing the potential biodiversity of the area should include provisions that encourage the redevelopment of forest habitat on those sites no longer supporting their equal share of forest. [ABSTRACT FROM AUTHOR]

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