Rangelands comprise nearly 40% of the
landmass of the United States. Largely unsuitable for cultivation, rangelands are primarily used for grazing
livestock. Navajo Nation sheepherders, for example, depend on quality rangeland to raise their herds of sheep, a
tradition central to their lives. The value of rangelands, however, extend beyond livestock support.
Rangelands provide habitat for rich biodiversity, clean air and water, and open space for recreation and spiritual
Rangelands are defined by the predominance of grasses, shrubs, forbs, and other grass-like plants. They include
grasslands, shrublands, woodlands, savannahs, tundra, most deserts, and riparian and wetland plant communities,
including marshes and wet meadows. Because of the exceptional diversity of habitats and climatic regions that rangelands
encompass, it is difficult to make broad generalizations on how they are impacted by climate change. Nevertheless, some
long-term trends are apparent.
A ubiquitous threat to rangelands is encroachment by non-native, invasive species, some of which benefit from increased
levels of atmospheric CO2. Higher in biomass than most native species, invasives greatly increase the threat of wildfire.
Warmer, drier summers in the western United States will likely intensify this threat. Some regions, such as the Great
Plains, have adapted to regular fire regimes. In the rangelands of the Southwest, however, fires have historically occurred
only once every several decades. Changes to this natural cycle could transform diverse desert scrub, scrub-steppe, and
desert savannah/grasslands to monocultures of invasive grasses and other plant species.
As biodiversity is lost, landscapes will become more susceptible to erosion. In the West, where precipitation is expected
to become less frequent and more intense, heavy rainfall events can wash away nutrient-rich topsoil. Intervening dry
periods cause wind erosion, which can have serious consequences for air quality. Higher amounts of dust settling on
mountain snowpack accelerates snowmelt and exacerbates water shortages during the summer months.
Erosion is also a major cause of desertification-land degradation that further deceases biodiversity and the economic
productivity of drylands. Desertification erodes the land's ability to perform its normal ecosystem services, such as
regulating water surface runoff and providing adequate forage for livestock and wildlife. Moreover, the Millennium
Ecosystem Assessment (MEA) reports that dryland soils sequester nearly a quarter of the world's organic carbon and
nearly all its inorganic carbon. Desertification can release this carbon back to the atmosphere and further exacerbate
climate change. The MEA notes that 4% of all worldwide carbon emissions result from desertification.
While the impacts of climate change are predominately negative, higher levels of atmospheric CO2 can enhance
plant growth. However, this growth might be mitigated by quantities of soil-bound nitrogen, a mineral necessary for
photosynthesis. In some areas of the Great Plains, higher growth rates diminish nitrogen levels, ultimately slowing plant
production. By contrast, enhanced production has stimulated nitrogen mineralization in short steppe ecosystems of Colorado.
Such differences demonstrate that the impacts of climate change are governed by a complex interplay of factors and vary by
For ungulates such elk, deer, cattle, bison, and caribou that depend on rangelands, vegetation quality is as important as
abundance. In the Great Plains, studies suggest higher levels of CO2 decrease the crude protein and soluble carbohydrate
content of forage. Digestibility also tends to decrease. Further, soluble sugars increase at lower temperatures, while
temperatures above optimal growth rates reduce sugar content.
Rangelands in the arid southwest region, particularly the Sonoran, Mohave, and Chihuahuan deserts, could be particularly
vulnerable to climatic change. Ecosystems already exist near their physiological thresholds for temperature and water
stress; any further changes could substantially alter the composition, distribution, and abundance of species. As temperatures
and the number of frost-free days increase, species will most likely migrate to the north or east, or to higher elevations.
Some species, such as those living on mountaintops, will have no place to go.
Rangelands, and the wide diversity of species they support, have played a pivotal role in sustaining Native peoples the
world over. Caribou, for example, are a fundamental part of traditional economies for peoples in the far North, including
the Gwich'in of Alaska and northwestern Canada, Saami and Komi peoples of Scandinavia and Russian western Arctic, and
numerous peoples of Siberia and the Russian Far East. Most climate scientists predict the Arctic will receive higher
amounts of precipitation as the climate warms. Increased snow depths during winter months and higher rates of insect
harassment during summer periods will decrease food availability, increase energy expenditure, and make caribou more
vulnerable to predators. These projected impacts suggest that caribou herds will decrease in number under climate change,
threatening the traditional economies that depend on them.
The bison, honored and respected by Plains tribes as sacred, embodies the centrality of the range in some indigenous
cultures. Plains Indians embraced the bison in almost every aspect of their existence: for food, clothing, medicine,
tools, and spiritual well being. After the U.S. government decimated the herds in the nineteenth century, conservationists
worked to re-establish the bison to the Great Plains. Range managers must now address an increasingly foreign landscape
as novel ecosystems emerge. The range will likely support fewer animals. Supplementary food sources might be necessary as
quality and abundance of forage decreases. As droughts become more frequent and intense, additional water sources will
likely have to be supplied. Tribes and conservationists working to bring back the bison will soon be faced with a difficult
reality: the past is longer a reliable guide for the future.
Dine be iiná, Inc. 2008. "Churro Sheep History." Available online at: http://www.navajolifeway.org/navajochurrosheep.htm.
[accessed 18 October 08].
Western Rangeland Partnership. 2006-07. "Topics: Western Rangelands and How They Work." Available online at:
Archer, S. and K. Predick. 2008. "Climate Change and Ecosystems of the Southwestern United States." Society for
Range Management (June 2008): 23-28.
Millennium Ecosystem Assessment. 2005. "Ecosystems and Human Well-being: Deserti?cation Synthesis." World Resources
Institute, Washington, DC. p. 18.
Morgan, J.A., J.D. Derner, G.D. Milchunas, and E. Pendall. 2008. "Management Implications of Global Change for Great
Plains Rangelands." Society for Range Management (June 2008): 18-22.
Archer, S. and K. Predick. 2008. p. 23.
Greenpeace. 1999. "Climate Change and Caribou." Available online at
http://archive.greenpeace.org/climate/arctic99/reports/carib2.html [accessed 1 November 08].