Grazing management on the Great Plains has been criticized for not more closely matching the presumed grazing patterns of bison. The critics assume that bison "flash grazed," that is, grazed heavily for a short time, then moved on, and did not return for months or even years. This assumption complements the traditional view of an annual north-south migration of the herds. However, evidence from explorers' and other travelers' journals contradict both flash grazing and annual north-south migration. In a few cases where prolonged continu- ous observations were made in the same favorable habitat, bison were seldom absent. In Canada, bison sometimes moved from the plains into the bordering aspen parklands during severe winter weather, but not regularly and not north-south. Throughout the Great Plains, bison num- bers were so great and so thoroughly spread over the country that if a herd moved on, they were quickly replaced by another, giving little opportu- nity for rest or regrowth of the plant communities. Bison appeared to move in response to local conditions of forage availability, as influenced by weather, fire, and previous grazing. In at least one case, bison re- mained on a depleted watershed until they starved, rather than moving to an adjacent watershed with adequate forage.
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