Western hemlock (Tsuga heterophylla): what the agencies record

This page reports what US federal publications say about one tree. It does not identify trees from descriptions or photos and does not say what should be done with any tree. The family overview, tree species in the agency records, explains the sources and holds the comparison table.

At a glance

Item	What the source records
Scientific name	Tsuga heterophylla (Raf.) Sarg., pine family
Other names	Pacific hemlock and west coast hemlock (Silvics); West Coast hemlock, Pacific hemlock and British Columbia hemlock (Wood Handbook)
Native status, USDA PLANTS	Native in Alaska, Canada and the lower 48 states
Size, Silvics	On the best sites old-growth trees commonly exceed 100 cm (39.6 in) in diameter, with a maximum of about 275 cm (108 in); heights of 50 to 61 m (165 to 200 ft) are not uncommon, with a maximum reported of 79 m (259 ft)
Age, Silvics	Maximum ages are typically over 400 but under 500 years; the maximum recorded, in excess of 700 years, is from the Queen Charlotte Islands
Green weight of the wood, NRS-38	41 lb per cubic foot, without bark

Native range

The Silvics of North America handbook (Agriculture Handbook 654, volume 1, 1990) calls western hemlock an important commercial tree of the Pacific coast and northern Rocky Mountains, thriving in humid areas. Along the coast it records a range north through the Coast Ranges from central California to the Kenai Peninsula in Alaska, a distance of 3,200 km (2,000 mi), and says it is the dominant species along the Coast Mountains and coastal islands of British Columbia and Alaska. Inland it grows on the western and upper eastern slopes of the Cascade Range in Oregon and Washington and on the west side of the Continental Divide in Montana and Idaho, north to Prince George, British Columbia. The handbook describes it as a pioneer on many sites yet commonly the climax dominant, and says the species is an important browse for deer and elk.

Cones and growth

Silvics describes western hemlock as monoecious. Flowering begins from mid-April to late April in western Oregon and runs into late May and June in coastal Alaska. The solitary pendent cones are 19 to 32 mm (0.75 to 1.25 in) long, and seed is usually ripe by mid to late September. Western hemlock forests, the handbook says, are among the most productive in the world: in paired British plantations the species commonly out-produced Douglas-fir and Sitka spruce, and on the Olympic Peninsula it out-produced Douglas-fir by 25 to 40 percent. It adds that mixed stands with Sitka spruce are especially productive.

Roots

The handbook calls western hemlock shallow-rooted and says it does not develop a taproot. The fine roots are commonly most abundant near the surface and are easily damaged by harvesting equipment and fire. Because of the shallow roots, it says pole-size and larger stands are subject to severe windthrow.

Wood

The Wood Handbook (FPL-GTR-282, 2021) says the heartwood and sapwood of western hemlock are almost white with a purplish tinge, with sapwood generally not more than 2.5 cm (1 in) wide. The wood often contains small, sound, black knots, and dark streaks caused by hemlock bark maggots generally do not reduce strength. It describes the wood as moderately light in weight and moderate in strength, hardness, stiffness and shock resistance, with moderately high shrinkage about the same as Douglas-fir, and says green lumber holds considerably more water than Douglas-fir and needs longer kiln-drying time. Principal uses it lists are pulpwood, lumber and plywood, with the lumber used in sheathing, siding, subflooring, joists, studs, planks, rafters, boxes, pallets, crates, flooring, furniture and ladders. Silvics says the wood treats well and is used for pilings, poles and railway ties.

Wood Handbook figure	Green	At 12% moisture content
Specific gravity (Table 5-3b)	0.42	0.45
Modulus of rupture, lbf per square inch (Table 5-3b)	6,600	11,300
Side hardness, lbf (Table 5-3b)	410	540
Moisture content of green wood, percent (Table 4-1)	85 heartwood, 170 sapwood	Not applicable

The green weight of the wood is in the NRS-38 table, the same figure used in the log weight calculator.

Pests and diseases the handbook names

Silvics (1990) says many agents affect growth, health and quality, and that no foliage diseases are known to cause serious problems. It names these agents by the names it used.

Fire and wind. Thin bark and shallow roots make the species highly susceptible to fire, and the shallow roots expose larger stands to severe windthrow. It also records frost damage in the Rocky Mountains and sensitivity to sulfur dioxide.
Dwarf mistletoe. Arceuthobium tsugense, called a serious parasite along the Pacific coast from California nearly to Glacier Bay, Alaska. The handbook says it increases mortality, reduces growth and provides an entryway for decay fungi.
Root and butt pathogens. Armillaria mellea, Heterobasidion annosum, Phaeolus schweinitzii, Laetiporus sulphureus, Inonotus tomentosus, Poria subacida and Phellinus weiri. Heterobasidion annosum is called the most serious root pathogen, with infection in unthinned stands ranging from 0 to more than 50 percent of trees. Phellinus weiri is described as common where Douglas-fir is or was a major part of the stand.
Bole pathogens. Echinodontium tinctorium, which causes extensive decay in overmature Rocky Mountain stands and is of little consequence on the coast, plus Heterobasidion annosum and Phellinus weiri.
Other fungi. Rhizina undulata, a root rot serious on burned sites, and a shoot blight that kills some trees in Alaska.
Insects. The western hemlock looper, which the handbook says has caused more mortality of the species than other insects, the western blackheaded budworm, whose defoliation outbreaks it records somewhere in the forests in most years since 1917, other loopers, a seedling-girdling weevil in coastal British Columbia, and the western larch borer in the Rocky Mountains.

The guide on reporting a pest in the United States and the Canada reporting page give the offices that take sightings of regulated pests. Who may apply pesticides is in pesticide licences by country.