When left undisturbed for centuries, forests mature into glorious old-growth groves. As young forests grow into older ones, they pass through a series of developmental stages, or succession. Fast-growing, sun-loving species such as alder and Douglas fir are replaced with slower-growing but more shade-tolerant types including western hemlock, western red cedar, and Sitka spruce. Thick underbrush gives way to ferns and the forest floor becomes soft with mosses and decaying woody debris. After about 200 years, the forest begins to display the distinctive features of an old-growth grove: a multi-layered canopy with trees and shrubs of various ages, the presence of large, standing dead trees (snags) and ground logs (nurse logs), and those massive old trees that make you practically fall over backwards trying to glimpse their tops.

Decomposers such as fungi, lichen, bacteria and invertebrates like beetles and termites are hard at work, constantly transforming dead plants and animals into nutrients for new life. Underground, a vast network of feathery white threads makes up the mycelium that seasonally fruits into mushrooms pushing up through the duff. Colonnades (trees standing in a row as a result of starting on nurse logs) and trees standing on stilts (due to seedlings sprouting on stumps that later decay away) provide especially interesting features to the forest landscape.

Animal species include black-tailed deer, Roosevelt elk, coyote, black bear, river otter and birds too numerous to mention. The Pacific temperate rainforests are so productive that the overall biomass totals up to four times that of any comparable forest in the tropics. In sheer mass of living and decaying material, these forests are more massive than any other ecosystem on the planet, sucking in carbon dioxide and pushing out oxygen at an impressive rate. Step into a coastal old-growth forest, and you will feel a coolness that is due not only to shade, but to the respiration of several-hundred-year-old trees.

Though nearly all of the Northwest's old-growth forests have been logged at some point in history, ancient groves can be experienced in Oregon at Ecola State Park in Cannon Beach, Oswald West State Park near Manzanita, Cape Lookout State Park south of Tillamook, Harts Cove near Lincoln City and Cape Perpetua immediately south of Yachats. On the Long Beach peninsula, explore Beard's Hollow at Cape Disappointment State Park at Ilwaco, Washington.