FORSite>Contents>The Forest Community

 

MOIST TEMPERATE CONIFEROUS FOREST BIOME

 

Lodgepole pine, a prolific seeder with serotinous cones, and quaking aspen, a prolific seeder and sprouter, are particularly well-adapted to fire, and are among the first to successfully invade a burn, almost regardless of altitude or latitude. Aspen is also common in areas of major soil disturbances, such as ravines swept by avalanches. Narrow leaf cottonwood (Populus angustifolia) is commonly found along the stream banks of this region and the lower plains.

 

Northern Rockies 

In the northern U.S., timberline decreases in altitude, as do the various accompanying vegetational zones. There is also a major change in species in some of the higher zones due to a wind corridor through the Cascades. This corridor allows moisture bearing winds from the Pacific to reach the western slopes of the Rockies, resulting in a wetter, milder climate than would normally be expected. Because of this, mountain hemlock (Tsuga mertensiana) is found growing with Engelmann spruce and subalpine fir (Abies lasiocarpa) in the higher altitudes. Western hemlock , western redcedar, and grand fir are found in the Douglas-fir zone. Western larch and western white pine (Pinus monticola) are the two principal successional species of the latter zone, both germinating and growing well on mineral seedbeds prepared by fire and other major disturbances.

 

Whitebark pine (Pinus albicaulis) is characteristic of the dry ridges and exposed areas of high altitudes. Its flexible branches allow it to withstand heavy snow loads but often the snow, coupled with extreme wind and cold, force the whitebark into its familiar, prostrate, ground-hugging form. The cones of the whitebark, unlike the other pines, fall from the trees and disintegrate, forming a fertile oasis among the thin, bare soils of the mountain top in which its seeds can germinate.

 

 

In the Canadian Rockies the subalpine zone is by far the most extensive, covering nearly all of the mountains. In the northern part of this range, white spruce of the northern forest is commonly found in association with subalpine fir. 
Sierra Nevadas

Physically, the Sierra Nevada Mountains range from northern to southern California, but floristically vegetation extends into the Cascade range of southern Oregon. The Sierras are oriented in a north-south direction, perpendicular to the prevailing westerly winds, and thus show distinct patterns of orographic precipitation. The west slopes of the Sierras rise gradually from the Great Valley, receiving very little precipitation; heavy rains fall near mid-slope as a result of condensation of cool moist air. The abrupt drop to the Great Basin on the east slope is very dry as the moisture-depleted air provides little precipitation.

The foothills of the west slopes form an open woodland between 500-2500 feet. Blue oak (Quercus douglasii) is the dominant tree, but is often found in association with digger pine (Pinus sabiniana).

 

The montane forest ranges from 2000-6000 feet in the southern Cascades and from 5000-8000 feet in the southern Sierras. There are six primary species in this zone, occurring either in pure stands or in various combinations. White fir is the dominant species at the higher altitudes in the zone where winters are long and snows are heavy; it is seldom found in pure stands. Pure stands of incense cedar (Libocedrus decurrens) dominate the richest sites in the lower sections of the zone. Ponderosa pine tends to dominate the lower margins of the zone since it is the most drought resistant of the six species. Jeffrey pine (Pinus jeffreyi), a close relative of ponderosa pine, has a higher tolerance for cold and frost and thus is commonly found in depressions and flats where cold air tends to gather, and at the upper extremes of the ponderosa pine zone where temperatures are much colder. Sugar pine reaches its maximum development in the middle of the montane zone where the climate is less extreme.

 

Douglas-fir (Pseudotsuga menziesii var. menziesii) tends to dominate the more moist, northern regions. A less common but more famous associate of these central montane species is the giant sequoia (Sequoia gigantea). The species occurs in scattered clumps throughout central California where annual precipitation is relatively high (40-60 inches) and soils are well drained. Until recently, the primary danger of these "sentinels of the Sierras" (many of 30 feet in diameter and 250 feet in height) was soil compaction resulting from tourism. The limited aeration destroyed the fibrous root system of the tree and altered water-holding properties of the soil, resulting in decreased vigor. Chaparral species commonly invade drier sites in the zone following fires. 

Moist Temperate Coniferous Forest Biome page    1    2    3    4