North America - Northwest Coast. Natural History

Extending from northern California northward to southern Alaska and pinned between the Pacific Ocean on the west and the Cascade Mountains and northern coast ranges on the east, the Northwest Coast of North America presents one of the most rugged and densely vegetated temperate coastal environments in the world.

Home to indigenous communities for at least ten thousand years, the region came into the orbit of European and U.S. commercial and imperial development only after the late eighteenth century. Since then development in the region has focused on extraction of rich natural resources in the form of forests and fisheries.

The resulting history includes a series of environmental crises due to depletion of those resources and a boom-and-bust economic cycle. Since World War II population in the region has shifted from struggling rural areas to a relatively small number of prosperous urban centers such as Portland, Oregon; Seattle, Washington; Vancouver, British Columbia; and Anchorage, Alaska. Throughout the region's changing history of development, the presence of the Pacific Ocean and its influence on climate, transportation, and the economy remain the central factors in defining this region and its land-use patterns.

Natural History. The Northwest Coast began to emerge from under the Cordilleran ice sheet—the last of the Ice Age glaciers of the region—seventeen thousand years ago. The topographical impact of those glaciers is one of the most visible characteristics of the region, especially north of 48° N latitude. They left deep valleys extending from the various mountain ranges toward the coast and wide troughs between the mountains.

The Puget Sound basin in Washington State was at the southern foot of the last continental ice sheet between the Cascade and Olympic Mountains. By ten thousand years ago ocean water returned to fill the resulting trenches to depths of 283 meters. Waters are even deeper in the Strait of Georgia, which separates the mountains of Vancouver Island from the Coast Range in southern British Columbia. An extensive series of fjords extends ocean water far into the interior of British Columbia.

The mountainous regions are a product of a complex combination of geologic forces. As part of the Pacific Rim "ring of fire," the region has a long history of volcanic eruptions and earthquakes as the Pacific tectonic plate slides under the North American plate. The Cascade Mountains reflect the legacy of ancient volcanoes in the southern portion of the range in northern California and Oregon but shift to a steeper, granitic composition from central Washington State northward to the range's terminus in southern British Columbia.

Volcanic Mount Rainier in Washington State is the high point of the Cascades at 4,393 meters. The coast ranges of British Columbia and southeast Alaska are the legacy of a combination of uplift and the addition of various geologic formations shoved into North America through the force of continental drift. Whereas the Cascades and the northern coast ranges define the eastern boundary of the Northwest Coast, other significant mountain ranges stand closer to the Pacific Ocean on British Columbia's Vancouver Island, the Olympic Peninsula in Washington, and the coast of Oregon.

The most distinct climatic feature of the Northwest Coast is its abundant rainfall. Weather patterns come from off the North Pacific laden with moisture. The mountain ranges force the air mass upward in elevation, causing it to cool, which precipitates the moisture into rain and snow. Mount Baker, in the northern Washington Cascades, received 28.96 meters of snowfall from July 1998 to June 1999, the most ever recorded for a single year anywhere.

The region also has the highest average annual snowfall on Earth. The abundant snowfalls provide for consistent water supplies and river flows throughout the year and feed the extensive system of glaciers that remains in higher elevations throughout the region. In the northern stretches of the coast, these glaciers reach sea level.

For most of the region precipitation falls as rain, mainly during winter. Rain is heaviest in the inland valleys near the coast, where clouds funnel inland before rising and releasing their moisture, Henderson Lake, on Vancouver Island, records the highest average annual rainfall in North America, 650.24 centimeters, higher than that found in any other temperate region. Most all of this abundant precipitation arrives during winter, from November to May, and summers are relatively dry.

This pattern is quite different from that in the interior of North America, where rain falls most during the growing season. Agricultural settlers in the moist climate of western Oregon in the mid- 1800s found that their desire to grow corn struggled in the face of the dry summers. Much of the forest vegetation of the region is determined not so much by a plant's ability to take advantage of the heavy rainfalls as by its ability to withstand summer droughts. Such is the case with the Douglas fir, the dominant tree of much of the region's forests.

Most of the human occupation of tire region has been in the low-elevation forested region due to the consistent presence of the western hemlock in undisturbed, old growth forests in the region. Dominant trees in this zone also include western red cedar, sitka spruce, and Douglas fir, which can grow to a height of 100 meters.

The skylines of today's cities, naturalists note, are often lower than the tops of tire forests that the urban development replaced. In the northern sections of this region in southeast Alaska, sitka spruce and yellow cedar become increasingly prevalent, whereas the Siskiyou region of southern Oregon contains a unique mix of conifer and broadleaf trees.

Two factors make the forests in the western hemlock zone of the Northwest Coast unique among the temperate forests of the earth. First, the dominance of coniferous evergreen trees over hardwood deciduous trees is the reverse of most forests in other temperate regions. Only on rocky slopes or sites of frequent disturbance will forests of tlie western hemlock zone consist mainly of deciduous big-leaf maple, vine maple, sitka alder, or red alder.

Second, the size and life span of the dominant coniferous trees surpass those found in any other forest community in the world. Tire mild winters provide an advantage to evergreens, which continue to grow year around, and the deciduous trees struggle through the dry summers. Undergrowth in these climates is an extremely dense combination of huckleberry, ferns, devil's club, salmonberry, and a variety of other woody shrubs. Measured in terms of biomass (the amount of living matter), these are among the most productive ecosystems on Earth, one hectare producing up to 30 metric tons of plant material per year.

Although prevalent, fire—ignited by both human and nonhuman sources—has been less influential in the Northwest Coast than in most of North America. Historical patterns of fire in the lowland coastal forests typically establish a cycle of intense, stand-replacing conflagrations that repeats on average every 230 years. Most indigenous communities did not use fire on a large scale to clear land because it was not a controllable or beneficial tool in such conditions.

They did use fire selectively, however, to maintain meadows for root and berry production. Important exceptions stand out in Oregon's Willamette Valley and the prairies of the southern Puget Sound region, where local villages used fire broadly on an annual basis to clear underbrush and to promote the growth of camas (plants of the lily family) and other food sources.

Tlie mountains create a complex mix of vegetation zones with changes in elevation; climate changes occur more rapidly ascending into the interior mountain ranges than traveling northward along the coast, where climate changes occur gradually.

Higher elevations have more Pacific silver fir, Alaska yellow cedar, mountain hemlock, and subalpine fir. Forests are less dense at these higher elevations, often existing in scattered clusters separated by open meadows. Heavy snows, shorter growing seasons, and more frequent fire regimes help to shape these montane (relating to the zone of moist, cool upland slopes below the timberline dominated by coniferous trees) environments.