Grazing

In the Great Plains ecosystems of the SOPN, grazing is a major natural ecosystem driver. The dominant grazers during pre-European times were bison, whose grazing was high intensity but low frequency. This type of grazing allowed most plant species time to recover during long non-grazed periods. Although grazing remains a dominant process in the Great Plains, the timing, intensity, species, and duration have all changed considerably. There is not strong evidence that large grazing herbivores, such as bison, played an important role in maintaining arid grasslands in the CHDN (Monger et al. 1998). The quality of grasslands in this region and on SCPN lands have also been reduced since the time of European settlement due to historic and present day livestock grazing. On SCPN lands, for example, livestock grazing has led to the wide-spread colonization of non-native plants such as cheatgrass (Bromus tectorum). Grazing in riparian areas of the American Southwest can affect water quality, increase erosion and sedimentation, reduce vegetative cover, and promote invasive plant establishment.