Ecological Effects Caused by the Grazing of Cattle on Public Lands
Jacob Janicke
Introduction
Spanish explorers introduced cattle to the west in the late 1500s and early 1600s (Borman 2005). Extensive grazing began in the 1800s and continued unmanaged until 1905 when the United States Forest Service (USFS) was created. By the late 1870s, livestock producers noticed negative ecological impacts occurring where cattle had previously grazed (Borman 2005). Although the USFS began attempts to curtail irresponsible grazing practices (Zier and Baker 2006), many people, ranchers and managers alike, considered livestock grazing sustainable if good management was implemented (Borman 2005). Grazing has occurred or is presently occurring on the majority of western public lands which includes Bureau of Land Management (BLM) lands, United States Forest Service (USFS) lands, federal wildlife refuges, federal wilderness areas, and also National Parks. In sixteen western states, 165 million acres of BLM land (94% of total BLM lands) and 103 million acres of USFS land are grazed by approximately 7 million head of livestock, primarily cattle (Fleisher 1994, Belsky and Blumenthal 1997). Ecologists determined that rangeland deterioration is occurring. They have gained this insight through a multitude of ways including: (1) historical records of altered ecosystems since cattle arrived, (2) studies from isolated areas such as mesa tops which provide a strong contrast to cattle susceptible adjacent lands such as in Mandany and West (1983), and (3) exclosures which were intentionally created to prohibit cattle from grazing (Fleisher 1994). Ecologists have concluded grazing affects vegetation in three different ways: function, composition, and structure. The first of these, ecosystem functioning, such as in riparian areas is commonly altered by cattle grazing in them. Riparian area’s efficiency of filtering water and increasing sediment deposition is reduced. Once this function becomes obsolete, effects such as decreased infiltration, increased runoff, and decreased vegetation productivity begin to occur (Fleisher 1994, Flenniken et al. 2001, McEldowney et al. 2002). The composition of vegetation is affected in two different ways: (1) selection of certain species and not others and (2) different susceptibilities of plant species to grazing effects (Fleisher 1994). Livestock aid in composition change by aiding the spread of exotic species by (1) spreading seeds with their feces, (2) disturbing areas allowing exotic species to thrive, and (3) reducing competition between exotic and native vegetation (Fleisher 1994, Belsky and Blumenthal 1997). For example, cheatgrass is efficient at invading areas and also successful at thriving in areas once it is established. Exotic grass invasion most notably occurs in the arid and semiarid west where livestock have most likely been the most altering disturbance (Fleisher 1994, Belsky and Blumenthal 1997, Loeser et al. 2007). The structure of ecosystems is often transformed due to many different causes. Grazing is one of the factors leading to the structure change in many western forest stands. Forests stands consisting of conifers are becoming increasingly denser. The once open park-like stands of ponderosa pines are now characterized by dense stands with increasing fuels. Cattle graze the herbaceous vegetation near the conifers decreasing the competition between the herbaceous vegetation and coniferous species. This in turn leads to densities of coniferous species increasing in forest stands (Fleisher 1994, Belsky and Blumenthal 1997, Mandany and West 1983)......continued in print edition.
