Rocky Mountains subalpine zone

The Rocky Mountains subalpine zone is the biotic zone immediately below tree line in the Rocky Mountains of North America. In Colorado, the subalpine zone occupies elevations approximately from 9,000 to 12,000 feet (2,700 to 3,700 m); while in northern Alberta, the subalpine zone extends from 1,350 to 2,300 metres (4,400 to 7,500 ft).

The climate of the Rocky Mountains subalpine zone is never warm, with summer highs reaching 75 °F (24 °C) on only the warmest days near the montane zone, and commonly failing to reach 60 °F (16 °C) near tree line; Frost may occur any day of the year. Although winter low temperatures may be warmer than those in nearby lower valleys, typically staying above −10 °F (−23 °C), prodigious snows blanket the region well into spring. Some drifts may linger into summer. Convectional precipitation, typically thunderstorms, often forms rapidly and frequently includes graupel or hail. Although uncommon, hurricane-force winds may develop and cause massive destruction such as the Routt Divide Blowdown.

In the North American Rocky Mountains, the region is characterized by a concentration of subalpine fir and Engelmann spruce and generally the exclusion of trees found more commonly at lower elevations such as aspen, ponderosa pine and lodgepole pine. In other areas, Engelmann spruce and subalpine fir mix with or give way to various pines, such as limber pine, whitebark pine and bristlecone pine, other firs such as Douglas-fir and silver fir, and various junipers and other hardy species. Previously burned areas may contain varying amounts, or even almost pure stands, of lodgepole pine. Ground cover in a previously burned forest area often includes two species of huckleberry.

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