The Rocky Mountains have many different types of plants and animals because of different weather and land conditions. These mountains are the largest mountain range in western North America, stretching from northern British Columbia, Canada, down to New Mexico in the southwestern United States. They rise from the Great Plains, which are at or below 1,800 feet (550 meters), up to peaks over 14,000 feet (4,300 meters). Weather and rainfall change a lot in the region, creating many different habitats. These include high mountain areas, lower mountain areas, and cold forests in British Columbia and Alberta; forests with many types of cone-shaped trees in Montana and Idaho; wetlands and grasslands where the mountains meet the plains; forests on the Yellowstone Plateau in Wyoming; forests at mid-elevations in Utah; and high mountain areas with very cold, thin soil in Colorado and New Mexico.
Many animals live in these areas, including plants-eating animals like elk, moose, mule deer, mountain goats, and bighorn sheep. Predators such as cougars, Canada lynx, bobcats, black bears, grizzly bears, gray wolves, coyotes, foxes, and wolverines also live there. In addition, there are many small mammals, fish, reptiles, amphibians, birds, and thousands of insects and soil creatures.
People living in the Rocky Mountains have caused some species to decrease in number, including certain types of fish, birds, and sheep. Gray wolves and grizzly bears were nearly gone from the U.S. part of the range, but they are returning because of efforts to protect them.
Setting
The Rocky Mountains stretch from the Liard River in British Columbia (at 59° N) to the Rio Grande in New Mexico (at 35° N). The highest peak is Mount Elbert, which reaches 14,440 feet (4,400 m). The range includes large valleys, such as the Rocky Mountain Trench and San Luis Valley. Annual precipitation varies from 10 inches (250 mm) in the southern valleys to 60 inches (1,500 mm) in the northern peaks. Average January temperatures range from 20 °F (−7 °C) in Prince George, British Columbia, to 43 °F (6 °C) in Trinidad, Colorado.
Biotic zones
Ecologists divide the Rocky Mountains into different biotic zones. These zones are determined by whether they can support trees and the presence of certain indicator species. Areas of the Rockies that do not support or have few trees include the prairie of the eastern foothills and the Alpine tundra. The foothill prairie grassland lies to the east of the Rockies, where the mountains meet the Great Plains near the Rocky Mountain Front (below about 1,800 feet or 550 meters). Alpine tundra occurs in regions above the treeline, which varies from 12,000 feet (3,700 meters) in New Mexico to 2,500 feet (760 meters) at the northern end (near the Yukon).
The USGS identifies ten forested zones in the Rocky Mountains. The more southern, warmer, drier zones are defined by the presence of pinyon pines/junipers, ponderosa pines, or oaks mixed with pines. The more northern, colder, wetter zones are defined by Douglas-firs, Cascadian species (such as western hemlock), lodgepole pines/quaking aspens, or firs mixed with spruce. Near the treeline, zones can consist of white pines (such as whitebark pine or bristlecone pine) or a mixture of white pine, fir, and spruce that appear as shrub-like krummholz. Rivers and canyons are home to unique forest habitats even in the more arid parts of the mountain range.
Biotic zones and vegetation types in the Rocky Mountains can be explained by elevation, aspect, and precipitation. Clinton Merriam recognized that two-dimensional diagrams of elevation and aspect described plant community distribution in the Southern Rocky Mountains. Other ecologists generally accepted this two-dimensional view until the complexities of environmental gradients such as temperature, precipitation, solar radiation, wind, soils, and hydrology could be described and modeled. Peet provided the most complete description of 10 major forest community types, which are summarized here. Two nonforested vegetation types, plains and alpine tundra, described by Sims and Billings, are added. Because of the variations in latitude and precipitation along this huge mountain range, the elevations presented here are general estimates.
Extensive investigations have been made of the forests of the Rocky Mountains. Weber cautioned that the vegetation zones "overlap and blend into each other considerably" in a landscape that is "always full of surprises." The resulting patchwork of vegetation types and disturbance regimes leads to a complex mix of side-by-side communities, wildlife habitats, and species distributions.
The eastern side of the Rocky Mountains is bordered by mixed-grass prairie to the north and by short-grass prairie to the south. The prairie, some of which has been described as the Montana Valley and Foothill grasslands, generally extends to elevations of 5,900 feet (1,800 meters). Dominant plants of the mixed grass prairie include little bluestem, needlegrasses, wheatgrasses, sand-reeds, and gramas, with dropseeds and cottonwoods in riparian zones. Short-grass prairie species include little bluestem, buffalo grass, western wheatgrass, sand dropseed, ringgrass, needle-and-thread, Junegrass, and galleta. Extensions of these vegetation types reach well into the Rocky Mountains along the valleys and on dry slopes. Plant species composition varies locally with changes in soil characteristics and topographic position—that is, from hilltops to valley bottoms.
Broad-leaved deciduous cottonwoods, alders, and willows, and aspens line streamsides and canyons. The herbaceous layer in riparian communities is often more diverse than upslope areas and adjacent forests. Riparian and canyon vegetation types are generally too thin or too small to be displayed on regional vegetation maps, but the habitat is extremely important in the arid West.
In the southern Rocky Mountains, a transition occurs between about 5,900 and 8,200 feet (1,800 and 2,500 meters), where plains communities are accompanied by pinyon pines. Two-Needle Pinyons and singleleaf pinyons are found in western Utah, alligator junipers and Rocky Mountain junipers grow to the south, and Utah junipers grow to the north. Many shrubs and grasses of the plains occupy the gaps between tree outcrops. Heavy livestock grazing is associated with the spread of junipers (by reducing competition from grasses), and fire suppression is partly responsible for their continued dominance.
The appearance of ponderosa pine woodlands varies from scattered individuals in low-elevation or rocky areas to dense forests at higher elevations or on deeper soils. Although ponderosa pines dominate the biomass of this community, other tree species such as Douglas-fir and Rocky Mountain juniper, shrubs (for example, raspberries, big sagebrush, gooseberries, currants, bitterbrush), and herb layers (such as mountain muhly, sedges, and sagebrushes) can develop. Typical intervals between natural fires are less than 40 years in most ponderosa pine forests. Fires that recur every 10–20 years suppress the growth of Douglas-fir saplings and encourage the growth of ponderosa pine.
In geological time, ponderosa pine ecosystems are relatively new to the foothills of the central Rocky Mountains. An even newer addition to the ecosystem, European-American settlers, devastated the ponderosa pine forests through logging for houses, fencing, firewood, mine timbers, and railroad ties, and with fire. The ponderosa pine forests were close to the developing population centers at the forest-prairie edge. The scale of the loss of ponderosa pine habitat is demonstrated best in several hundred paired photographs from the early 20th century and 1980s. However, nearly all the paired photographs also reveal that the most important feature of the ponderosa pine ecosystem is its resilience. Ponderosa pine seedlings establish quickly in disturbed sites. Research in the Front Range of Colorado shows a tenfold increase in ponderosa pine biomass since 1890 in many stands. This regeneration has restored habitat for many wildlife species but has also led to unnatural forest densities in many areas.
In the southern Rocky Mountains, lower slopes of ponderosa pine communities can be accompanied by Gambel oaks, other oak species (for example, Emory oaks, silverleaf oaks, netleaf oaks), and shrubs (such as sumacs, buckbrushes, and mountain-mahoganies). In the absence of fire, the oak stands may
Fauna
The Rocky Mountains provide important homes for many types of wildlife, including elk, moose, mule deer, white-tailed deer, pronghorn, mountain goats, bighorn sheep, black bears, grizzly bears, gray wolves, coyotes, cougars, bobcats, Canada lynx, and wolverines. The largest moose herds in North America live in the forests near the Alberta-British Columbia foothills. Scientists do not know much about the status of most species in the Rocky Mountains because there is not enough information. Information about many night-time animals, such as bats and raccoons, and about small creatures like insects, lichens, mosses, fungi, and soil microbes is also missing.
European-American settlers in the mountains have hurt many native species. Some species that have declined include western toads, greenback cutthroat trout, white sturgeons, white-tailed ptarmigans, trumpeter swans, and bighorn sheep. In the U.S. part of the Rocky Mountains, top predators like grizzly bears and gray wolves were removed from their original homes, but they have started to return because of conservation efforts and reintroduction programs. Other species, like bald eagles and peregrine falcons, are also recovering. Species such as black bears, mountain lions, small mammals, and common birds and plants are considered stable because their populations are not changing quickly.
Although most animals in the Rocky Mountains are insects, scientists know very little about them. An entomologist said, "We don’t know how many moth and butterfly species live in any area of North America." In some parts of the western U.S., information about moths and butterflies is available. Colorado has many different habitats, from prairies to tundras, that support about 2,000 species of butterflies, moths, and skippers. More than 1,000 of these species live in the Front Range of Colorado. Some grasshopper species are found only on specific mountain tops in Colorado, New Mexico, Arizona, Nevada, and Utah. The Rocky Mountain locust, which was a major problem for farmers in the 1800s, is now extinct. Heavy grazing in river valleys in Montana and Idaho likely destroyed the locust’s breeding areas forever.
Amphibian populations around the world are shrinking because of habitat loss, non-native fish, logging, more ultraviolet radiation, and disease. Amphibians in the Rocky Mountains are also declining, following the same trends. Western toads, which were once common between 7,500 and 13,800 feet (2,300 and 4,200 meters) in the central and northern Rocky Mountains, now live in less than 20% of their old range, from southern Wyoming to northern New Mexico. Between 1974 and 1982, 11 western toad populations in Colorado’s West Elk Mountains disappeared due to a bacterial infection and other environmental factors. In Rocky Mountain National Park, only 3 breeding sites for western toads remain. In the past 20 years, western toads have disappeared from 83% of their historical range in Colorado and 94% of their sites in Wyoming. Northern leopard frogs are also declining in the Rocky Mountains.
The Rocky Mountains are home to many coldwater fish, including rainbow trout, bull trout, lake trout, cutthroat trout, brown trout, brook trout, golden trout, mountain whitefish, Arctic grayling, and Dolly Varden. Many of these fish were introduced to the area, such as rainbow, brown, and brook trout.
Colorado River cutthroat trout were once common in mountain streams of the Green and Colorado rivers, but by the 1930s, non-native brown, brook, and rainbow trout had taken over. Some cutthroat trout populations survived in isolated areas and were used to restore the species to parts of their old range. One of the last strongholds for cutthroat trout was Trappers Lake in Colorado’s Flat Top Mountains. In 1984, a flood brought brook trout from nearby Crescent Lake into Trappers Lake. By 2003, brook trout made up 40% of the lake’s fish population. Brook trout have an advantage over cutthroat trout because they spawn in the fall. By the time cutthroat trout hatch in August, brook trout may already be large enough to eat them. Colorado Parks and Wildlife is trying to control the brook trout population using nets and selective removal.
Rio Grande cutthroat trout live in about 700 miles of streams in the Santa Fe National Forest, which is about 91% of their historical range. These trout were considered for protection under the Endangered Species Act from 2008 to 2014 but were removed from the list in 2014. They are the southernmost subspecies of cutthroat trout. However, because of population losses and reports of Rio Grande cutthroat trout in Mexico and Texas, scientists are unsure how far south the species once lived. In 1955, the Rio Grande cutthroat trout was named the state fish of New Mexico.
Greenback cutthroat trout were thought to be extinct in 1937, but scientists found them in Colorado in the 1950s. A campaign by Colorado Division of Wildlife and federal agencies helped reintroduce the fish to parts of their old range. In 1996, the greenback cutthroat trout became Colorado’s state fish. In 2012, researchers found that the only pure population of greenback cutthroat trout lived in a small stream outside their native range. Since then, the fish have been reintroduced to Zimmerman Lake and Sand Creek.
Yellowstone Lake in Yellowstone National Park, Wyoming, is the site of a recent major environmental problem. Non-native lake trout, which are from the Great Lakes, were introduced to Yellowstone Lake. Native Yellowstone cutthroat trout may not compete well with lake trout because lake trout eat cutthroat trout. If cutthroat trout populations continue to decline, grizzly bears could lose an important food source after hibernation because cutthroat trout spawn in streams and are easy prey for bears, while lake trout spawn in deep water. The National Park Service is trying to remove lake trout using commercial fishing crews. So far, over 1.7 million lake trout have been removed from Yellowstone Lake. For every lake trout removed, about 41 cutthroat trout are saved. Cutthroat trout have shown some recovery, but other threats, like whirling disease brought by non-native brown trout, remain.
Mountain whitefish have not declined much in their native range. They are found in many parts of Wyoming, Montana, and Idaho, as well as in Colorado’s Y