Washington State, often called the “Evergreen State,” owes its nickname to its extensive and diverse forest lands. This remarkable variety is a direct result of the state’s distinct geography, primarily the Cascade Mountain range, which bisects the region. The mountains create a sharp climatic division, separating the cool, wet temperate rainforests of the west from the dry, continental climate of the east. This environmental gradient supports an array of forest types, from massive, ancient conifers near the coast to drought-tolerant pines in the inland valleys.
The Dominant Conifers of Western Washington
The western side of the Cascades, which receives high annual rainfall and experiences mild temperatures, is dominated by enormous evergreens. These species thrive in the moisture-rich environment. The state tree, the Douglas Fir (Pseudotsuga menziesii), is perhaps the most iconic species, known for its incredible height and longevity. Mature Douglas Fir can grow over 250 feet tall, and its thick, deeply furrowed bark provides natural resistance to low-intensity fires.
Western Hemlock (Tsuga heterophylla) is a highly shade-tolerant conifer that frequently grows in the understory of these forests. This tree is characterized by its feathery, drooping branch tips and short, soft needles of unequal length. Western Hemlock often dominates later successional stages of the forest due to its ability to germinate and persist in low light conditions.
Western Red Cedar (Thuja plicata) is recognized by its flat sprays of scale-like leaves. Its decay-resistant wood made it historically important for indigenous peoples. Near the immediate coast, especially on the Olympic Peninsula, the Sitka Spruce (Picea sitchensis) takes prominence, flourishing in the saltwater spray and high humidity. The Sitka Spruce is distinguishable by its sharp, stiff needles and can grow to be one of the largest spruces in the world. The dominance of these four conifer species gives Western Washington its reputation for immense, old-growth forests.
Deciduous Trees and Hardwoods
While conifers dominate the overall forest biomass, deciduous trees play an important ecological role. The Bigleaf Maple (Acer macrophyllum) is the largest broadleaf tree in the Pacific Northwest, easily identified by its massive leaves that can span up to a foot in width. Its branches are often heavily draped with mosses, liverworts, and ferns, supporting a complex micro-ecosystem. Bigleaf Maple is a common sight along riparian zones and in the lower elevations of Western Washington, where it contributes significant organic matter to the forest floor.
Red Alder (Alnus rubra) is the Pacific Northwest’s most abundant hardwood and a classic pioneer species, rapidly colonizing disturbed sites after logging or fire. Red Alder is a nitrogen-fixer, hosting bacteria that convert atmospheric nitrogen into a usable form. This process significantly improves soil fertility, making the land more hospitable for the slower-growing conifer species that will eventually succeed it.
Other common hardwoods include various species of cottonwood and aspen, which often form dense stands in river valleys and floodplains. Their fast growth and ability to thrive in open, sunny areas contrast sharply with the long-lived, shade-tolerant strategies of the dominant conifers.
Tree Species of the Inland and Eastern Regions
East of the Cascade Crest, the climate shifts dramatically due to the rain shadow effect. This drier environment supports species adapted to hot summers and cold winters. The Ponderosa Pine (Pinus ponderosa) is the signature tree of the lower and mid-elevations in Eastern Washington, often growing in open, park-like stands.
This pine is highly drought-tolerant and fire-resistant, possessing long needles clustered in bundles of three, and a distinctive orange-brown bark on mature trees. The thick bark protects the living cambium layer from the low-intensity surface fires that historically maintained the open structure of these forests. Ponderosa Pine stands typically transition to mixed-conifer forests at higher elevations.
The Western Larch (Larix occidentalis) is another fire-adapted conifer, but it is unique because it is deciduous. The Western Larch sheds its needles each autumn after they turn a brilliant golden yellow. This makes it highly resistant to fire, second only to the Ponderosa Pine in its range.
Western Larch is one of the longest-lived species in the region, often found in mixed stands with Douglas Fir and Grand Fir (Abies grandis). At the highest elevations of the eastern Cascades, species like Engelmann Spruce (Picea engelmannii) and Subalpine Fir (Abies lasiocarpa) are found, tolerating the severe cold and deep snowpack near the treeline.