RENO, Nev.--Livestock grazing advocates may have new ammunition in the dispute over the long terms effects of livestock grazing. An article released this week in the Journal of Rangeland Management documents a comprehensive research project that looked for differences between grazed and un-grazed rangelands in Nevada.
The study, called "Vegetation change after 65 years of grazing and grazing exclusion," found that there are few differences among plant populations on grazed and un-grazed lands.
"Advocates for the removal of livestock often do not provide scientific evidence of long-term damage from properly managed livestock grazing," said Barry Perryman, co-author of the study and assistant professor of animal biotechnology at the University of Nevada, Reno. "On the other hand, livestock grazing supporters have little documented evidence of grazing having any beneficial effect on the land."
A University of Nevada research team, however, sought to look at grazing from a scientific perspective. The team looked to history for data.
In 1934 the Taylor Grazing Act established grazing controls on public land. At that time, the U.S. Forest Service--working with the University of Nevada's Agricultural Experiment Station and the Taylor Grazing Service--wanted to be able to measure the recovery rates from prior grazing practices. In order to compare grazed rangelands with rangelands that had been un-grazed, 28 exclosure sites--four-acre parcels enclosed by barbed wire to keep out livestock--were built at that time. Today, 16 of those sites remain intact and provided the basis for the study.
"There have been a lot of exclosure-type studies," Perryman said "But this is one of the longest, if not the longest, study of its kind."
To determine what effects the grazing of large ungulates--cattle and sheep, for example--have had on such things as the amount and variety of vegetation, the research team conducted in 2001 to 2002 a meticulous examination of the ecologies both inside and outside the exclosures. The researchers then subjected their findings to a thorough statistical analysis.
After analyzing the data, the researchers concluded that, "light-to-moderate grazing in the Great Basin certainly has no ill effects on the ecosystem." What few differences exist between grazed and ungrazed rangelands are minor and "can even be somewhat beneficial," Perryman said.
One such benefit is that within the exclosures there is more vegetative ground cover, while outside there are more plants as well as a greater variety of plants.
The study specifically addresses the view that rangelands are irreparably damaged by domestic grazing in the Great Basin and should subsequently be off-limits to livestock. Perryman said that the study has the potential to help resolve the sometimes bitter debate between ranchers--who have legal authorization to graze livestock--and those who believe that grazing does harm.
"From an ecological standpoint we can argue that if we remove the grazing infrastructure from public rangelands, we would see some adverse consequences," he said. "We'd see less variety and too much ground cover, for example, as well as more cheatgrass and the potential for more range fires."
Cheatgrass is a highly flammable invasive weed. In areas dominated by cheatgrass, fires that historically occurred once every 50 to100 years are now occurring every two to five years, according to the researchers. The exclosures appear to contain more cheatgrass than the grazed areas, Perryman said.
Graduate student Danielle Courtois, now with the New Mexico Bureau of Land Management, was the lead author of the study. Animal biotechnology Associate Professor Hussein Hussein, of Nevada, is also a coauthor.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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