The negative effects of equid grazers in semi-arid ecosystems of the American West has been considered to be disproportionate to the influence of native ungulates in these systems because of their large body size, hoof shape, and short history on the landscape relative to native grazers. Tools which can model the degree of influence of various grazers in an ecosystem and separate these effects from those caused by other variables (climate, anthropomorphic disturbances) can be useful to managers in determining location of non-native grazer impacts and assessing the effect of management actions targeted at different grazer populations. We used remotely sensed data to determine the influence of native grazers, non-native grazers, and climate on vegetation productivity at wildlife refuges in Oregon and Nevada. Our findings indicate that equid grazer biomass density and precipitation in winter and spring had the greatest influence on Normalized Difference Vegetation Index (NDVI) values. Our results concur with those of other researchers who found that drought exacerbated the impacts of grazers in arid systems.
Zeigenfuss, Linda C.; Schoenecker, Kathryn A.; Ransom, Jason I.; Ignizio, Drew A.; and Mask, Tracy
"Influence of nonnative and native ungulate biomass and seasonal precipitation on the vegetation production in a Great Basin ecosystem,"
Western North American Naturalist: Vol. 74
, Article 3.
Available at: http://scholarsarchive.byu.edu/wnan/vol74/iss3/3