Spatial vegetation-environment relationships and distributional changes in the presettlement Minnesota prairie-forest boundary.

Abstract

The prairie-forest boundary region in Minnesota spans 650 km along a northwest-southeast axis and is often considered one of the most abrupt grassland-forest transitions in the world. Historically, this region separated tallgrass prairie vegetation to the south and west from forest vegetation to the north and east, while land conversion since presettlement has eliminated over 95% of original prairie and continues to convert and fragment forested lands. Ecological boundaries such as the prairie-forest transition are considered critical landscape elements that control the fluxes of organisms, materials, and energy between ecosystems. While the significance and characteristics of ecological boundaries has been often discussed in scientific literature, there are few studies that provide empirical support for boundary concepts. In particular, studies are lacking that evaluate vegetation-environment relationships across boundaries. In this thesis, I use the presettlement prairie-forest boundary as an example of an ecological boundary to address the following issues: 1) the influence of spatial scale and spatial heterogeneity in the controls of vegetation, 2) the spatial nature of a vegetation-climate relationship across the boundary, and 3) range distributional shifts since presettlement in tree taxa common to the boundary region.