Livestock and Alien Weeds
Livestock cause weed invasion by grazing and trampling native plants; clearing vegetation, destroying the soil crust and preparing weed seedbeds through hoof action; and transporting and dispersing seeds on their coats and through their digestive tracks. 1
"At the community scale, livestock may be the major factor causing weed invasions."
Weeds spread on western federal lands at an estimated 4000-5000 acres per day. 2
Introduced weeds alter and damage western landscapes by increasing fire frequency,
reducing biodiversity and wildlife habitat, and increasing topsoil loss. 3
Competition with or predation by alien species is the second-ranked factor for the listing of all threatened and endangered species. 4
Livestock grazing for "weed control" is counterproductive-research demonstrates that grazing harms native species, reduces species richness and vegetative cover, while promoting alien plant growth in many ecosystem types. 6
Livestock transport weed seeds into uninfested sites on their coats and feet and in their guts; preferentially graze native plant species over weed species; create patches of bare, disturbed soils that act as weed seedbeds; and destroy microbiotic crusts that stabilize soils and inhibit weed seed germination. Grazing also creates patches of nitrogen-rich soils, which favor nitrogen-loving weed species; reduces concentrations of soil mycorrhizae required by most western native species; and accelerates soil erosion that buries weed seeds and facilitates their germination. 5
Cheatgrass, a noxious weed perpetuated by grazing and wildfire, 7
is now the dominant species on 100,000 million acres - 158,000 square miles
- or one-third of the sagebrush grasslands in the Intermountain West. 8
1. Belsky, A. J. and J. L. Gelbard. 2000. Livestock grazing and weed invasions in the arid west. Oregon Natural Desert Association. Bend, OR (citations omitted).
2. Belsky, A. J. and J. L. Gelbard. 2000. Livestock grazing and weed invasions in the arid west. Oregon Natural Desert Association. Bend, OR: 4; Bureau of Land Management. 2000. Use of weed-free forage on public lands in Nevada. Fed. Reg. 65-54544. USDI-BLM.
3. Belsky, A. J. and J. L. Gelbard. 2000. Livestock grazing and weed invasions in the arid west. Oregon Natural Desert Association. Bend, OR: 4 (citations omitted).
4. Wilcove, D.S., D. Rothstein, J. Dubow, A. Phillips, and E.. Losos. 1998. Quantifying threats to imperiled species in the United States. Bioscience 48: 609.
5. Belsky, A. J. and J. L. Gelbard. 2000. Livestock grazing and weed invasions in the arid west. Oregon Natural Desert Association. Bend, OR: 3. The Oregon Natural Desert Association published Belsky and Gelbard's report, the best review ever written on domestic livestock grazing and invasive weeds. It is available in Adobe PDF format at http://www.publiclandsranching.org/htmlres/PDF/BelskyGelbard_2000_Grazing_Weed_Invasions.pdf.
6. See Kimball, K. and P. M. Schiffman. 2003. Differing effects of cattle grazing in native and alien plants. Conservation Biology 17(6): 1681-1693 (grazing harms native plant species and promotes alien plant growth in California grasslands); M. L. Floyd, T. L. Fleishner, D. Hanna, P. Whiefield. 2003. Effects of historic livestock grazing on vegetation at Chaco Culture National Historic Park, New Mexico. Conservation Biology 17(6): 1703-1711 (native species richness and shrub and grass cover higher inside long-term grazing exclosures than on nearby grazed sites in northern New Mexico); T. L. Fleishner. 1994. Ecological costs of livestock grazing in western North America. Conservation Biology 8(3): 629-644 (p. 631, table 1) (native species richness and vegetative cover higher in absence of domestic livestock in a variety of western ecosystem types); A. Jones. 2001. Review and analysis of cattle grazing effects in the arid West, with implications for BLM grazing management in southern Utah: a literature review submitted to the Southern Utah Landscape Restoration Project. Wild Utah Project. Salt Lake City, UT.
7. See E. J. Rawlings, K. K. Hanson, R. L. Sanford, J. Belnap. 1997. The striking effects of land use practices and Bromus tectorum invasion on phosphorous cycling in a desert ecosystem of the Colorado Plateau. Bull. Ecological Soc'y of America 78: 300; J. Gelbard. 1999. Multiple scale causes of exotic plant invasions in the Colorado Plateau and Great Basin, USA. M.S. thesis. Duke University, Nicholas School of the Environment. Durham, NC.
8. Rosentreter, R. 1994. Displacement of rare plants by exotic grasses. Pages 170-175 in S. B. Monsen and S. G. Kitchen. PROC. ECOLOGY AND MANAGEMENT OF ANNUAL RANGELANDS. Gen. Tech. Rep. 313. Intermountain Research Station. Ogden, UT: 170 (citing R. Mack. 1981. Invasion of Bromus tectorum L. into western North America: an ecological chronicle. Agro-Ecosystems 7: 145-165).