A major floristic boundary in Minnesota: an analysis of 280 taxa occurring in the western and southern portions of the state

A prominent floristic boundary is identified by combining distribution maps based on herbarium records of 280 taxa that occur in western and southern Minnesota. A set of boundary dots was plotted for each taxon with the help of a grid overlay, and the coordinates of the dots in the set were tabulated and mapped by computer. The map shows a band of concentration Of species limits that runs roughly north-south in the west and bends eastward in the central and eastern parts of the state. When subsets of the 280 taxa based on habitat preference are mapped independently, the band remains distinct. Single factors of climate and landscape alone are inadequate to explain the position and strength of the floristic boundary. The next most simple hypothesis proposes that the boundary results from an abrupt change in ecosystem type, from a woodland kept open by the interaction of fire with vegetation, topography, and soils to a closed forest where fire was less frequent. The concentration of limits implies that for many species migration had reached an equilibrium with ecosystem factors under the present climate.