List of Animals of The Rocky Mountains - Biotic Zones

Biotic Zones

Ecologists divide the Rocky Mountain into a number of biotic zones, defined by whether they can support trees, and the presence of one or more 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 fall to meet the Great Plains at the Rocky Mountain Front (below roughly 1,800 feet (550 m)). Alpine tundra meanwhile occurs in regions above the treeline, which varies from 12,000 feet (3,700 m) in New Mexico to 2,500 feet (760 m) at the northern end (near the Yukon).

The USGS defines 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. Finally, 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. Merriam recognized that two-dimensional diagrams of elevation and aspect described plant community distribution in the southern Rocky Mountains. Other ecologists generally embraced 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 gross generalizations.

Extensive investigations have been made of the forests of the Rocky Mountains. Weber cautioned that the vegetation zones "overlap and telescope into each other considerably" in a landscape that is "always full of surprises." The resulting patchwork mosaic of vegetation types and disturbance regimes leads to a complex of side-by-side communities, wildlife habitats, and species distributions.