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Plants and Animals:
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on the Prairie
Bison affect both the structure and the functioning of prairie communities. They prefer grasses to forbs and prefer some grasses over others (Vinton, et al 1993; Kreuger, 1986). Thus by reducing populations of their favored forage, they improve habitat for other species thereby increasing biodiversity. Bison also affect the productivity of grasses. Vinton and Hartnett (1992) report that grazing can stimulate growth in tallgrass prairie grasses in the short term, but decrease it over longer periods of sustained grazing. Prior to European settlement bison migrated in search of better food. It is difficult to precisely reconstruct the influence of bison on the range because large herds with unimpeded migration no longer exist. However, bison grazing was probably high intensity, low frequency. In other words, a herd would intensely graze an area, then move on, so that the grazed area could then recover. This form of grazing pressure differs from fenced herds, which may be low intensity, but high frequency. This kind of grazing may have a stronger influence on community composition, because the bison are continually removing their favored forage plants, leaving the species they disfavor.
Bison also affect prairie vegetation through the development of wallows. Wallows are shallow depressions created when bison trample the ground and roll in the exposed soil (Polley, and Collins, 1984). Water is retained in wallows during the wet seasons because of soil compaction. Changes in soil nutrient status and pH also occur in and around bison wallows. The end result is the creation of a habitat suited to wet to mesic plant communities and the maintenance of habitat diversity on the prairie (Damhoureyeh et al., 1997; Gibson, 1989).
Nitrogen is recycled in bison manure which creates patches of elevated soil nitrogen on the prairie. These patches support different kinds of plants.
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