Weed Management Systems for Rangeland

Rangelands of approximately 0.4 billion hectares are an essential resource in the United States (Thomas and Ronniger, 1965). Most wildlife and 75% of all domestic livestock depend upon rangelands for survival (Williams et al., 1968). Weeds and brush infestations cause incalculable economic losses by reducing rangeland forage production, water yield, wildlife habitat, and recreational use. Cost of handling livestock, livestock death and injury losses, and human allergies are greatly increased by dense stands of poisonous, thorny, or allergenic pollen producing plants. Estimates of total area infested vary, but weeds and brush are a problem on nearly all grazing land (National Academy, 1968). Weed and brush problems have been created by introduction of exotic plant species, grazing animals, reduction of fire, transport of weed seed by grazing animals, climatic fluctuations, cultivation and subsequent abandonment, local denudation and increased commerce (Vallentine, 1989), and many other factors. More recently today’s higher CO₂ levels have been suggested to favor C3 520(shrublands) rather than C4 (grasslands) plants and may partially explain why native woody plants dominate (Mayeux et al., 1991).