Western Hemlock

Tsuga heterophylla is native to the Pacific Coast of North America.

• Ranges from the Kenai Peninsula in south-central Alaska southward along the coast through British Columbia, Washington, Oregon, and into northwestern California
• Also occurs in the interior wet belt of British Columbia and northern Idaho
• Found at elevations from sea level to approximately 1,800 meters in the Cascade Range
• The most abundant conifer in the coastal forests of British Columbia and southeastern Alaska
• First described by the Scottish botanist David Douglas, later formally named by the Franco-American botanist André Michaux
• Forms the climax forest type over much of its range, eventually replacing Douglas fir in the absence of disturbance
• A defining species of the North American temperate rainforest, one of the most productive forest ecosystems on Earth

Tsuga heterophylla is a large to very large evergreen conifer with a narrow, conical crown and drooping leader.

Size:
• Typically 30 to 55 meters tall, with exceptional specimens reaching 70 to 75 meters
• Trunk diameter: 0.6 to 2.5 meters
• Crown is narrowly conical, with a characteristically drooping terminal leader

Bark:
• Young bark is thin, smooth, and brownish-gray
• Mature bark becomes dark reddish-brown, thick, and deeply furrowed into broad, flat ridges

Needles:
• Flat, linear, 5 to 20 mm long and approximately 1 to 2 mm wide — distinctly unequal in length on the same branch (the source of the name "heterophylla")
• Dark yellowish-green above, with two conspicuous silvery-white stomatal bands beneath
• Arranged in flat, feathery sprays
• Rounded at the apex, grooved above
• Persist for 3 to 5 years

Cones:
• Pendulous, ovoid, small, 1.5 to 2.5 cm long
• Light brown when mature, with thin, papery, rounded scales
• Resemble small, pendant thimbles
• Seeds approximately 2 to 3 mm long with a short wing

Western hemlock is a dominant species in the temperate rainforests of the Pacific Northwest.

Habitat:
• Thrives in the wettest forest environments west of the Cascade crest, where annual precipitation can exceed 3,500 mm
• Also common in the interior wet belt of British Columbia and northern Idaho
• Extremely shade-tolerant, often forming dense understory beneath Douglas fir and western redcedar
• Prefers moist, acidic, well-drained soils but tolerates a range of conditions
• Often found on moist alluvial sites, stream terraces, and lower mountain slopes

Ecosystem role:
• A foundation species of the Pacific coastal rainforest, providing critical habitat structure
• Seeds consumed by pine siskins, crossbills, chickadees, and red squirrels
• Dense canopy provides essential cover for Roosevelt elk, black-tailed deer, and northern flying squirrels
• The northern spotted owl relies on old-growth forests where western hemlock is a major component
• Fallen logs and snags create nurse logs for seedling establishment of multiple tree species
• Extensive root systems play a critical role in soil stabilization and watershed protection
• Less susceptible to the hemlock woolly adelgid than its eastern counterpart