Forest Service Western An American Wood United States Department of Agriculture Hemlock FS-240 Western hemlock is an important com- mercial softwood species in the Western United States and Canada. The largest stands are found in the humid coastal regions of Oregon, Washington, British Columbia, and Alaska. The wood is used for structural lumber, molding, roof decking, veneer, and paper.
F-308993 An American Wood
Western Hemlock (Tsuga heterophylla (Raf.) Sarg.) James M. Cahill1
Distribution
Western hemlock grows along the Pacific coast from the Kenai Peninsula in Alaska to northwestern California (fig. 1). Inland from the coast, it is found on the western slopes and upper eastern slopes of the Cascade Range of Washington and as far south in Oregon as the Siskiyou Mountains. Farther inland, western hemlock grows on the west side of the Continental Divide from just east of Prince George, British Columbia, south through north- ern Idaho and northwestern Montana. About 80 percent of its distribution in the Rocky Mountains is in British Columbia.
The fastest growing stands are found in the humid coastal regions of Oregon, Washington, British Columbia, and Alaska, and on the lower slopes of the Cascade Range in Washington and Oregon. In the Rocky Mountain region, dry summers limit western hemlock to primarily northerly slopes and moist creek bottoms.
Western hemlock is usually subordinate in stands that include Sitka spruce (Picea sitchensis) and Douglas-fir (Pseudotsuga menziesii), but it sometimes dominates and is found in pure stands in coastal areas. The pure western hemlock forest is a true climax type and follows the subclimax types of Sitka spruce and Douglas-fir west of the Cascades and western white pine (Pinus monticola) in the northern part of its inland range.
Description and Growth
Western hemlock is the largest of the four American hemlocks and, under the
1Research Forester, U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station, Portland, Oreg . Figure 1–Natural range of western hemlock. F-532739 2 An American Wood
Figure 2–Needles and cones of western F-308997 hemlock. best growing conditions, can reach The bark is relatively thin, even on old seeds per cone. The seeds are only more than 3 feet in diameter and 225 trees, and deeply fissured with broad, 1/16 inch long and average 300,000 feet in height. Forest-grown western flat, russet-brown ridges. The inner per pound. Wind is the main factor in hemlock trees produce long, clear sym- bark is streaked with purple. seed dissemination; some seeds are metrical boles and shallow, wide- blown more than a mile from their spreading root systems. The crown Western hemlock is a prolific seeder. It source. length of old-growth trees and of produces some seed every year and young, tightly spaced trees is usually heavy seed crops at least every 8 years. With adequate moisture, germination is short. As with all hemlocks, the ter- Cones can be found on trees less than excellent on a diverse range of material minal shoot normally droops, giving it 20 years old, but, in general, cone pro- including moss, humus, decaying litter, a characteristic look that provides a duction begins between 25 and 30 and mineral soil. In coastal regions, quick method of identification. The years. Cones ripen in late summer and where the forest floor is often densely needles are 1/4 to 3/4 inches long, flat- early fall. At maturity, they are 3/4 to covered with vegetation, hemlock tened, and dark, shiny green (fig. 2). 1 1/4 inches long and hold 30 to 40 grows from decaying stumps and logs.
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Western hemlock is very tolerant of Related Commercial Species shade and survives under a variety of seedbed conditions. Natural regenera- Published information on timber tion can be obtained through harvesting volume often includes western hemlock methods that vary from individual tree with other species. Estimates of net selection to clearcutting. sawtimber volume, for example, usually include mountain hemlock The main causes of hemlock mortality (Tsuga mertensiana). Hemlock lumber are wind, fire, and snow. Losses from is usually marketed in species groups snowbreak are most severe in the in- such as “Hem-Fir” which includes land range, whereas significant losses California red fir (Abies magnifica), from windthrow occur in the coastal grand fir (A. grandis), noble fir (A. areas. The shallow root system of procera), Pacific silver fir (A. western hemlock contributes to its amabilis), and white fir (A. concolor). susceptibility to fire and wind damage. Supply Several trunk, butt, and root rots are found on western hemlock Fomitopsis The sawtimber volume (trees greater Figure 3–Yearly lumber production of western annosus, F. pinicola, Phellinus pini, P. than 9 inches in diameter) of western hemlock, 1967 to 1979. weirii, Ganoderma applanatum, Poria hemlock growing in the United States subacida, Echinodontium tinctorium, was estimated to be 256.9 billion board Armillariella mellea, and Polyporus cir- feet in 1977. About 45 percent of this cinatus. Echinodontium tinctorium (In- volume was in Alaska, 35 percent in or Oregon lands is prohibited by dian paint fungus) causes extensive Washington, 17 percent in Oregon, and Federal and State laws, with minor decay in standing trees and is one 3 percent in Idaho and Montana. exceptions. reason western hemlock is classified as Mountain hemlock is included in these an inferior species in its inland range. estimates but accounts for only a small The paper industry uses hemlock as a Dwarf mistletoe (Arceuthobium cam- percentage of the total volume. source of pulp. In Washington and pylopodum) is a common parasite and Oregon, hemlock makes up more than is thought to reduce annual growth, Production 50 percent of the volume consumed by lower wood quality, and increase mor- the paper industry. Hemlock logs are tality. The presence of flutes, or deep In the last decade, western hemlock ac- also an important source of veneer vertical grooves with ingrown bark, in counted for more than 20 percent of bolts. In 1976 hemlock accounted for the bole is a problem in southeast the total lumber production in about 5 percent of the total volume Alaska. Extensive fluting decreases Washington and Oregon, and more than peeled for veneer in Oregon and about yields of fiber and limits use of trees 50 percent of the total Alaska produc- 15 percent of the volume in for sawtimber. Insects that attack tion. Figure 3 shows the yearly produc- Washington. western hemlock include western tion for Washington and Oregon com- hemlock looper (Lambdina fiscellaria bined and for Alaska. Characteristics and Properties lugubrosa), western black-headed bud- worm (Acleris gloverana), western Primary products produced in Oregon The heartwood of western hemlock is larch roundheaded borer (Tetropiun and Washington include dimension almost white, with a purplish tinge. velutinum), and the hemlock sawfly lumber, molding stock, and cants The sapwood is sometimes lighter in (Neodiprion tsugae). (squared-off timbers) for export. Alaska color. It varies in thickness from 1 to 3 production is predominantly cants. inches and is usually difficult to Common Names distinguish from heartwood. Western Western hemlock is the major species hemlock wood is moderately light in Western hemlock has been known by exported from Washington and Oregon weight and moderate in strength, hard- several common names, including west and accounted for more than 50 percent ness, stiffness, and shock resistance. coast hemlock, hemlock spruce, Pacific of all log exports in 1980. The export Shrinkage is moderately large–about hemlock, western hemlock spruce, market is second only to lumber pro- equal to that of Douglas-fir. The western hemlock fir, gray fir, silver duction in log use. Most exported logs average specific gravity is 0.42 based fir, and Alaska pine. Currently, it is are cut from private lands and lands on ovendry weight and green volume; usually referred to as hemlock or managed by the State of Washington. the average weight at 12-percent western hemlock. Exporting logs cut on Federal and State moisture content is 31 pounds per cubic
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foot. Green western hemlock contains hemlock a preferred species over its where the light color is desirable for considerably more water than Douglas- major competitors for industrial lumber natural finishes. Western hemlock is fir and requires a longer period of dry- and for finish lumber where even- preferred over Douglas-fir where a ing to reach the same moisture content. wearing and good machining charac- minimum of grain raise, splintering, or teristics are important. annual-ring delamination is important. Ring shake, or the separation of wood Western hemlock ranks only slightly cells in the outer part of the latewood In both nail-holding ability and ten- behind Douglas-fir and western larch in (denser wood, formed late in the grow- dency to split when nailed, western strength, which is one of the reasons it ing season), is more common in hemlock has an intermediate rank. In is widely used in construction. hemlock than in other softwoods. paint-holding ability, it ranks below the Typically, shake is found in the basal cedars and white pines but above The light-colored heartwood makes ex- portion of large hemlock trees and Douglas-fir. The wood is free from cellent newsprint because minimum causes considerable loss of lumber and resin and is classed as nondecay- bleaching is required to establish the veneer. resistant. It contains many small, black desired brightness of paper. Also, the knots that are generally tight. The dark lack of resin in hemlock makes the Western hemlock trees frequently con- streaks sometimes seen in hemlock wood easily pulped by the sulphite tain some wetwood, which means that lumber result from activities of the process, which is sensitive to resin parts of the standing wood have hemlock bark maggot in living trees. content. unusually high moisture levels. Wet- wood, generally, is difficult to dry to a Principal uses When used in the manufacture of consistent moisture content. Wetwood plywood, western hemlock veneer is is also sometimes associated with ring Western hemlock is used to produce a generally used for inner plys. shake. wide variety of products. The light col- or of the wood, lack of pitch, and The bark of western hemlock is often Cell wall thickness in the annual ring ability to take a varnish finish well used for decorative horticultural pur- of western hemlock shows no distinct make hemlock the major source of roof poses. As such, it is often preferred change from the wood formed early in decking, particularly in exposed ceil- over the bark of Douglas-fir, which the growing season to wood formed ings. It is also excellent for laminating contains needlelike fibers and causes later. This characteristic makes western stock, moldings, and architectural trim discomfort to handlers.
References
5 An American Wood
6 February 1984
This publication supersedes an unnumbered American Wood leaflet, Western Hemlock, issued October 1945.
U.S. GOVERNMENT PRINTING OFFICE : 1984 O - 415-844 (Item 6)