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MOIST TEMPERATE CONIFEROUS FOREST BIOME

 

 

The subalpine zone extends approximately 2000 feet above the upper montane limit. The climate consists of long winters with heavy snows and short, dry summers with cool temperatures. Red fir (Abies magnifica) is the major climax species here, often occurring in pure, even-aged stands. At the upper end of the subalpine zone red fir mixes with Jeffrey, western white and lodgepole pines. The latter is an important fire-related successional species. White fir and mountain hemlock are less common associates. 
Near the timber line, whitebark, limber and foxtail pines are the dominant species, often occurring in scattered clumps interspersed by alpine meadows. These are all small tree species, rarely surpassing 30 feet in height, limited by the severe environment and poor soil conditions. 

The subalpine zone of the east slope is comprised mainly of timber line species of the western slope--whitebark, limber and foxtail pines. Lodgepole pine grows quite extensively on these eastern slopes, as it does throughout most of the West. Red fir occurs only in scattered areas. 

Jeffrey pine is the dominant species in the montane zone of the east slopes. Here it forms open park-like stands, similar to, but in place of, the ponderosa pine of the western Sierras.

 

Cascade Mountains 

The Cascades extend from southern Oregon to British Columbia. The western slopes are generally considered to be part of the moist temperate coniferous forest biome, with which they were included and discussed in this treatment of biomes. However, above 5000 feet there exists a subalpine forest of mountain hemlock, noble fir (Abies procera), subalpine fir, and pacific silver fir (A. anabilis). Timber line here occurs near 6000 feet, much lower than at the same latitude in the Rockies. This is attributed primarily to the heavier snow loads experienced in the Cascades.

The eastern slopes of the Cascades are drier than the west and have species similar to those of the northern Rockies. The subalpine forest is much the same as on the western slopes. The upper montane forest consists of Douglas-fir, western hemlock, and western redcedar. Western larch and western white pine are the common successional species following fire. 

 

The lower slopes of the eastern Cascades are especially dry, with rainfall ranging from 10-40 inches per year, and a long dry summer dominating the climate. In this area, ponderosa pine thrives in vast, pure stands. This tree has a long, fast-growing tap root that allows it to reach a more constant water supply than that available to most plants. Regeneration of ponderosa pine is also particularly successful because the seedlings are able to withstand prolonged drought by obtaining moisture from the night dew. 

 

Interior British Columbia 

In the interior of British Columbia, the Pacific Coast mountains and the Rockies merge. Here the land takes the shape of a high, rolling plateau that is covered by a forest of white spruce, Douglas-fir, lodgepole pine and aspen. Farther to the north these species are replaced by an association of lodgepole pine, subalpine fir, and Englemann spruce. In northern British Columbia, the Yukon, and Alaska the forest changes to white spruce and subalpine fir. White spruce is the primary successional species on the nutrient rich sites, while black spruce (Picea mariana) forms an edaphic climax on the bogs.

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