The RMGB region is home to exceptionally diverse natural resources, and to many national monuments and parks, including Yellowstone, Grand Teton, Glacier, Rocky Mountain, Grand Mesa, Capitol Reef, Great Basin, and Canyonlands National Parks. The region is also the site of extensive designated wilderness areas, with roughly 80% of its land held in public ownership.

Many plant and animal species and habitats occur in this area, many of which are not found elsewhere in the nation. For example, pikas (related to rabbits) and mountain goats can be found in the alpine areas of the RMGB, and grizzly bears populate some sub-alpine areas in Montana. Unique fish species -- the Rocky Mountain cutthroat and the Colorado sucker -- inhabit the region's streams. This diversity of natural resources is spread unevenly over the region. For example, Great Basin sagebrush covers vast continuous expanses of the region. In contrast, alpine lakes, whitebark and bristle cone pines, and sub-alpine meadows exist only in isolated patches.

This region is also characterized by wide variability in climate -- variability that could increase or decrease with changes in climate and affect the region's ecosystems, both positively and negatively. In fact, the ecosystems of the region have already been affected by invasive grass and woody species, such as cheatgrass and tamarisk, which are supplanting native species.

Extractive resource use, through timber harvest, livestock grazing, coal and hard-rock mining, and oil and natural gas production, has traditionally been a key element of this region's economy. However, many RMGB natural resources and ecosystems are now stressed from environmental consequences of high production demands, overuse, competing land-use resulting from urban and suburban growth, and the escalating needs of a rapidly expanding population. For example, most of the region's water resources have been significantly altered through the extensive network of dams that support water storage and delivery systems. Climate changes as well as existing challenges could further stress the region's natural resources and ecosystems.

Perhaps the major factor responsible for the climatic variations from one place to the next in the RMGB is the topographic variation. Precipitation increases and temperatures decrease at progressively higher elevations. The result is a climatic gradient around mountain ranges from warm and dry, and hence arid or semi-arid conditions in the valleys and bases of the ranges, to moist and cool or cold conditions on the mountain ridges.

These temperature and precipitation zones produce the wide range of vegetation zones that characterize the West. Among the most extensive are the desert and shrub-steppe zones in the valley bottoms and feet of the mountains. There are various combinations of grassland, deciduous shrubs, and pygmy conifers at the next higher levels. Two or more zones of coniferous forest occur at the intermediate and higher mountain elevations; alpine tundra exists on the tops of the higher mountains. Although competition between plants can play a role, the position of these zones is primarily determined by shortage of moisture and high temperatures at their lower boundaries, and the combination of cold temperatures, snow, and wind at their upper limits.

Animal species vary across these different habitat types, depending on their adaptation to the vegetation and climatic conditions. Some avoid climatic extremes by migrating up and down slope seasonally, or by migrating latitudinally (north or south).

Given that temperature and precipitation levels influence where plants and animals will be found (ecological zones), changes in the composition and distribution of the plants and the presence of animals are expected in connection with climate change. Those changes are likely to take place over several time scales. Vegetation dominated by long-lived woody species (trees) tends to change slowly (e.g., over a century or more) although these changes are likely to be accelerated by unexpected secondary factors like fire, disease, and insects. On the other hand, short-lived grasses and perennial vegetation can change quickly. Faunal (animal) changes are likely to depend on whether species require fast- or slow-changing vegetation types for habitat, or whether the physical (e.g. available space on a mountain side for a large population) environment puts limitations on their populations.

With an increase in precipitation an increase in fire frequency could occur in the short-term in the Great Basin shrub steppe. Wildfires can convert the natural plant communities to those dominated by non-native annual plants. This would happen because fires kill the shrubs that would otherwise out-compete the annuals and prevent their growth. Heavy precipitation stimulates vegetative growth that increases the amount of combustible plant material, and lightning associated with storms increases fire frequency. The result could well be significant reduction of biodiversity, not only drastic reduction in plant diversity, but near elimination of the animals that depend on the native vegetation. Fire frequency could also increase in the mountain areas if higher temperatures create drier conditions as occurred in 2000.

Some animal species that are forced into seasonal altitudinal (up and down mountains) migration to avoid winter conditions could benefit from warmer temperatures. Large ungulates (hoofed animals -- deer, moose, mountain goats, etc.) that now descend in the fall to limited low-elevation winter ranges, which are considered population bottlenecks, could perhaps remain on larger summer ranges that are currently inaccessible because of deep snow. The same could be true for seasonally migrating avian (bird) species.

Over longer time scales, the biotic (life) zones in the West that are determined by elevation would be expected to move up or down with the projected climate changes. Indeed the paleoecological record (ancient environmental record determined by pack rat middens, tree rings, etc.) shows marked elevational shifts, both up and down, as climates have changed over the past 25,000 years. Many western ecologists expect that the zones will move upslope with rising temperatures. In many cases, the mountaintop alpine tundra species are projected to be eliminated as the alpine coniferous forests move-up and take over the terrain. But with the potential of an increase in precipitation reducing the dryness constraints on the zones' lower limits, it is possible that some zones, or at least some of the species, might move downslope.

Similarly, some plants have also been projected to move northward as temperatures rise. The major example for the Intermountain West is the northward movement of southern hot deserts of New Mexico and Arizona into the Great Basin. But if the projected 50-100% increase in precipitation becomes a reality, the region is more likely to change to a grassland, savanna, or even woodland than remain a desert.

Whatever the eventual patterns of climate change, the current reality is that the existing species in the many zones in the RMGB region have evolved patterns that have allowed them to exist together. This evolution has occurred under the climatic conditions of the past few centuries. For some species these patterns are less than optimal, while for others, they are the most favorable conditions for growth and reproduction. Projected changes in climate therefore have the potential to favor some species and be detrimental to others. Each species would respond individually and in relationship to other competing species. The likely result will be fundamentally changed and shifted natural communities throughout the region. The invasion of non-native plant species -- already a problem of great concern in the West -- would be likely to be assisted by the breakdown of the current ecosystems.

Aquatic ecosystems would also be affected by climate change. The ecology of western streams developed in response, for example, to the water cycle created by winter snows, spring run-off, and summer dryness. These ecosystems have been significantly altered by dams and reservoirs that change stream habitat of native fish species by changing stream velocities, temperatures, seasonal patterns of flow, and substrates (stream bottoms -- e.g., rocky, muddy, etc.). Aquatic ecosystems have been altered by the appearance of non-native fish species that prey upon and compete with native species. Some 38 non-native fish species are now present in Utah's lakes and rivers. In many western streams, native cold-water species have retreated into limited, high-elevation areas that have undergone few changes and continue to experience low temperatures. Air-temperature increases would raise water temperatures and create more favorable conditions for warm-water species that would compete with the cold-water species, which are already living at a disadvantage in waters no longer at the cool temperatures they prefer.

While lumber and grazing in the RMGB has been a declining part of the region's economy, significant shifting of forest and rangeland plants associated either directly with climate change, or indirectly through increased frequencies of fire, disease and insect outbreaks, and non-native plant invasion, would likely increase the decline. Lifestyles, livelihoods, and associated industries based on these uses would be at risk. Also, outdoor recreation and tourism, now major contributors to the region's economy, and related businesses, could be affected as will be discussed in the next section.

While there is little that humans can do to avoid climate change impacts on natural ecosystems, the following strategies could help in reducing or addressing the consequences of climate-induced stresses on this region's natural resources and ecosystems.

• Increase awareness about possible climate change and its potential impacts among timber, mining, and ranching stakeholders and land- and resource-management agencies so that such groups can prepare for change.
• Document the current regional distribution, abundance, and climate sensitivity of water, fauna (animals), and flora (plants) -- both natural and invasive/exotic species as the basis for possible reestablishment of stressed species in more suitable environments, and keep seed banks for reintroduction of species.
• Promote improvement in the region's water-use efficiency, identify areas of high expected disturbance, and adapt management plans to meet growing multiple demands.
• Reduce current stresses on the environment, for example due to overgrazing, erosion, etc.
• Protect forest diversity by modifying current harvesting practices and pest control, and preparing productive drought- and heat-resistant species for commercial use. Reduce the intensity of forestry in vulnerable areas.