Pacific Temperate Rain Forest (WWF Ecoregion) - Ecology

Ecology

The ecosystem of Pacific temperate rain forests is so productive that the biomass in the best sites is at least four times greater than that of any comparable area in the tropics (Davis 2000). In sheer mass of living and decaying material - trees, mosses, shrubs, and soil - these forests are more massive than any other ecosystem on the planet. In part, this is due to the rarity of fire. Unlike drier forests, which burn periodically, temperate rain forests are naturally subject to only small-scale disturbances, such as blow-downs and avalanches.

This rain forest spans a wide range of latitude - from about 40 degrees north to about 60 degrees north. The differences in climate from south to north create several major forest zones, characterized by different species.

• At the southern limit in northern California is the "coast redwood zone".
• Beginning at the California/Oregon border, and extending through the north end of Vancouver Island is the "seasonal rain forest zone". The major tree species here are Douglas fir, Western Red Cedar, Sitka spruce, and Western Hemlock.
• Beyond the northern end of Vancouver Island, is the "perhumid rain forest zone". Douglas fir wanes as a dominant species, and the forest is primarily made up of western red cedar, Sitka spruce, and western hemlock.
• The Gulf of Alaska begins where the fjords of southeast Alaska end, and marks the transition into "sub-polar rain forest". Here the forest occupies only a very narrow strip between the ocean and the icy alpine zone. The cedar trees no longer thrive in this harsher climate, and the dominant trees are limited to Sitka spruce, and western and mountain hemlock.
• The northern limits of the rain forest are scattered in thin bands in the northern Prince William Sound, Kenai Fjords, eastern Kodiak Island, and western Cook Inlet.