The Wisconsin Bumblebee		Tue, Nov 24, 2009

Map showing the tension zone in Wisconsin, and the July 70 F, isotherm
from Medler, J.T. and D.W. Carney. "Bumblebees of Wisconsin,", pg 6 (Figure 1).

Wisconsin is divided into two areas, southwest and northeastern. The Southwest is prairie and the northeast is boreal. These areas are separated by a transition or tension zone. The tension zone is not only a boundary for plants and animals but also indicates moisture differences. This zone is closely aligned with the July 70 F degree isolines in Wisconsin. The change in temperature and climate appears to determine the distribution of bumblebee species, limiting species ranges to either the northeastern or southwestern Wisconsin.

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