TRUETT ET AL 2001 (Joe C., senior biologist with the Turner Endangered Species Fund, author of Land of Bears and Honey: A Natural History of East Texas and Circling Back: Chronicle of a Texas River Valley, and coeditor of The Natural History of an Arctic Oil Field: Development and the Biota, Michael Phillips, Executive Director of the Turner Endangered Species Fund, B.Sc. in Ecology, Ethology, and Evolution from the University of Illinois, and M.Sc. in Wildlife Ecology from the University of Alaska, Kyran Kunkel, affiliate senior conservation scientist for the Turner Endangered Species Fund and Ph.D. in wildlife biology from the University of Montana, and Russell Miller, Turner Enterprises, Great Plains Research, “Managing Bison to Restore Biodiversity”, 11 pg. 128, http://digitalcommons.unl.edu/greatplainsresearch/541)
Fire interacts with physical features and grazing to intensify the patchwork effect on the vegetation. Prior to settlement, fire in tallgrass prairie occurred as often as once everyone to five years (Collins and Gibson 1990). Fire frequency generally declined with distance westward, as tall grasses were replaced by mid- and shortgrasses(Sieg 1997). Fire reduces the height of vegetation and attracts foraging bison for at least the first few years postburn (Shaw and Carter 1990; Vinton et al. 1993; Hartnett et al. 1996; Knapp et al. 1999). Grazing in turn reduces natural fire frequency (Hobbs 1996), causing ungrazed sites to burn selectively thereafter. Burning tends to favor grass dominance over that of woody species, which in fire-prone prairies may be restricted to riparian zones, draws, north-facing slopes, and other topographic refuges where fires seldom burn (Sieg 1997). Burning in the absence of grazing tends to reduce vegetative diversity.Burning tallgrass prairie selects for the dominant warm-season grasses and against cool-season grasses, forbs, and woody species (Vinton et al. 1993; Hartnett et al. 1996). This reduces the structural diversity of the vegetation as well as the species richness (Gibson and Hulbert 1987). The encroachment of woody species into grasslands since European settlers instituted fire suppression suggests the dramatic effects that fire previously had induced in Great Plains grasslands (Wright and Bailey 1980).