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Conservation

An author of the Food and Agriculture Organization (FAO) report Livestock's Long Shadow, stated in an interview:

Grazing occupies 26 percent of Earth's terrestrial surface... feed crop production requires about a third of all arable land... Expansion of grazing land for livestock is also a leading cause of deforestation, especially in Latin America... In the Amazon basin alone, about 70 percent of previously forested land is used as pasture, while feed crops cover a large part of the remainder.

Much grazing land has resulted from a process of clearance or drainage of other habitats such as woodland or wetland.

According to the opinion of the Center for Biological Diversity, extensive grazing of livestock in the arid lands of the southwestern United States has many negative impacts on the local biodiversity there.

Cattle destroy native vegetation, damage soils and stream banks, and contaminate waterways with fecal waste. After decades of livestock grazing, once-lush streams and riparian forests have been reduced to flat, dry wastelands; once-rich topsoil has been turned to dust, causing soil erosion, stream sedimentation and wholesale elimination of some aquatic habitats

In arid climates such as the southwestern United States, livestock grazing has severely degraded riparian areas, the wetland environment adjacent to rivers or streams. The Environmental Protection Agency states that agriculture has a greater impact on stream and river contamination than any other nonpoint source. Improper grazing of riparian areas can contribute to nonpoint source pollution of riparian areas. Riparian zones in arid and semiarid environments have been called biodiversity hotspots. The water, higher biomass, favorable microclimate and periodic flood events together produce higher biological diversity than in the surrounding uplands. In 1990, "according to the Arizona state park department, over 90% of the original riparian zones of Arizona and New Mexico are gone". A 1988 report of the Government Accountability Office estimated that 90% of the 5,300 miles of riparian habitat managed by the Bureau of Land Management in Colorado was in unsatisfactory condition, as was 80% of Idaho 's riparian zones, concluding that "poorly managed livestock grazing is the major cause of degraded riparian habitat on federal rangelands".

A 2013 FAO report estimated livestock were responsible for 14.5% of anthropogenic greenhouse gas emissions. Grazing is common in New Zealand; in 2004, methane and nitrous oxide from agriculture made up somewhat less than half of New Zealand's greenhouse gas emissions, of which most is attributable to livestock. A 2008 United States Environmental Protection Agency report on emissions found agriculture was responsible for 6% of total United States greenhouse gas emissions in 2006. This included rice production, enteric fermentation in domestic livestock, livestock manure management, and agricultural soil management, but omitted some things which might be attributable to agriculture. Studies comparing the methane emissions from grazing and feedlot cattle concluded that grass-fed cattle produce much more methane than grain-fed cattle. One study in the Journal of Animal Science found four times as much, and stated: "these measurements clearly document higher CH production for cattle receiving low-quality, high-fiber diets than for cattle fed high-grain diets".