When people think of the Pacific Northwest, they naturally think of trees. This region is one of the best places in the world to grow trees, boasting more biomass (weight of plants per acre) than even the famously exuberant tropical rainforests. But if you expect that all the forests of the Northwest look the same, think again.
Factors like soil, elevation and fire vulnerability affect the type of forests you visit here, but the most important consideration is this: are you east of the Cascade Mountains, or west?
East of the Cascades, you’re liable to be walking through open ponderosa pine or deciduous forest (composed of trees that drop their leaves annually); on the west side, you’re apt to find yourself surrounded by the Christmas-tree-like conifers, the image most people have of Northwest forests.
The difference in the forest types is largely explained by the Cascade volcanoes (extending from Mount Shasta in California to Mount Garibaldi in British Columbia), which unfairly divvy up the rainfall arriving from the Pacific Ocean. The forests on the west side receive far more precipitation than those on the east side. That explains why the west side is more luxuriant than the east, but it doesn’t explain why conifers grow better here than do hardwood trees — or why conifers grow better here than anywhere else in the world.
It’s not just a matter of rainfall. As Daniel Mathews points out in Cascade-Olympic Natural History: A Trailside Companion, “It’s when the rain falls that makes our region unique. Generally, a wet temperate climate on this planet either supplies rainfall throughout the year, or concentrates it in the warmer months.”
The west side of the Cascades has notoriously wet winters and gloriously dry summers. The drought that the west side experiences during summer months gives conifers a growth spurt advantage over deciduous trees. During dry spells, trees can close tiny openings (stomata) on their leaves to avoid drying out but this also shuts down their ability to photosynthesize (create food from sunlight).
Conifers Rule
While conifers can make up for this down time during other seasons of the year, deciduous trees are at a disadvantage in summer drought: this is the time of year they do the bulk of their photosynthesizing. Thus, on the west side of the Cascades, conifers rule.
In general, certain tree species are found in specific elevations and areas in our region: Douglas firs and hemlocks favor mid-elevations on the west side; ponderosa pines prefer lower elevations on the east side, etc. To identify a specific tree in a forest, one easy method is to use a tree key, like the one in Trees & Shrubs of Washington (Lone Pine Press) by C.P. Lyons.
A key leads you to a species conclusion one step at a time simply by making one choice or another. Start with how the needles look: are they like the ones on a Christmas tree (needle) or do they have distinct little overlapping sections (scale-like)? Your answer moves you toward the left or right side of the key, landing you on another set of choices until you identify the tree.
There are plenty of Northwest guidebooks that describe not only the trees but the multitude of other plant and animal species associated with them.
Old-Growth Trees
The Pacific Northwest is also known for old-growth trees. Individual trees in these stands are typically at least 400 years old. Scientists, however, require more than ancient trees to describe a forest as “old-growth.” There are certain characteristics that all old-growth forests share. In addition to large, old trees with a multi-leveled canopy (uppermost tree branches and foliage), scientists look for large-standing dead trees and large logs on the forest floor and in streams.
Until relatively recently, these components were seen as detrimental to the health of a forest. It seemed logical that fallen trees in rivers and streams impeded adult salmon on their way to spawn, as well as their eventual offspring heading downstream to the ocean. It appeared that dead standing trees (snags) harbored insects liable to kill living trees. And clearly, logs took up space that could be put to ‘better’ use by new seedlings.
Forest managers have since recognized that old growth has its own management system. The fallen trees in rivers help adult and fry salmon by slowing the current, thereby creating eddies and quiet resting pools. Snags house insects as well as the animals that feed on them, including pileated woodpeckers, nuthatches, and chickadees. One study showed that 79 species of birds and mammals make use of snags.
The fallen trees also provide habitat and food for at least 130 species of animals as well as for other trees. Seeds that happen to land on a dead tree have a much better start at life than those that land on the forest floor; the hitchhikers are able to access the water and nutrients stored in their benefactors. Recognition of the important roles played by both standing and fallen dead trees has led to changes in the management of forests throughout the Northwest.
Regardless of whether the forests you visit are old-growth or a relatively young stand, or whether you find yourself on the east side or west side of the Cascades, the best way to experience the trees of our region is to see them for yourself.
Recommended reading:
Cascade-Olympic Natural History: A Trailside Reference,
Daniel Mathews; Audubon Society of Portland, 1988.
National Audubon Society Regional Guide to the Pacific Northwest, Peter Alden; 1988.
Northwest Trees, Stephen F. Arno; The Mountaineers Books, 1977.
Plants and Animals of the Pacific Northwest: An Illustrated Guide to the Natural History of Western Oregon, Washington, and British Columbia, Eugene N. Kozloff; University of Washington Press, 1978.
Plants of the Pacific Northwest Coast: Washington, Oregon, B.C. and Alaska, Jim Pojar and Andy MacKinnon; Lone Pine Press, 2004.
River-Walking Songbirds & Singing Coyotes: An Uncommon Field Guide to Northwest Mountains, Patricia K. Lichen and Linda Feltner; Sasquatch Books, 2001.
Secrets of the Old Growth Forest, David Kelly and Gary Braasch; Gibbs Smith, 1990.
The Enduring Forests: Northern California, Oregon, Washington, British Columbia, and Southeast Alaska,” Ruth Kirk and Charles Mauzy; The Mountaineers Books, 1996.
Trees & Shrubs of Washington, C.P. Lyons; Lone Pine Press, 1999.
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