Forest Products

Commercial Species

Western Hemlock (Tsuga heterophylla)

The genus Tsuga contains about 14 species native to North America [4] and southern and eastern Asia [10]. The word tsuga is the Japanese name for the native hemlocks of Japan. The word heterophylla means "with other (different or various) leaves."

The Tree

Western hemlock trees reach heights of 200 feet, with diameters of 3 feet. An exceptional specimen was recorded at 259 feet tall, with a diameter of 108 inches.

General Wood Characteristics

The heartwood and sapwood of western hemlock are brown with a purplish tinge. Both are light reddish and nearly indistinguishable from each other. The sapwood, which is sometimes lighter in color, is generally not more than 1 inch thick. The wood often contains small, sound, black knots that are usually tight and stay in place. Dark streaks are often found in the lumber; these are caused by hemlock bark maggots and generally do not reduce strength. The wood is moderate in its hardness, stiffness, and shock resistance and has moderately large shrinkage (about the same as Douglas-fir). Green hemlock lumber contains considerably more water than Douglas-fir and requires a longer kiln drying time. Trees may contain wet wood and/or have ring shake.

Distribution

Western hemlock is the most abundant tree species grown in Southeast Alaska. It is native to the Pacific coast region from southern Alaska (Kenai Peninsula) southeast through southeastern Alaska and western British Columbia to western Washington, western Oregon and northwestern California. The species is also found in the Rocky Mountain region from southeastern British Columbia south to northeastern Washington, northern Idaho and northwestern Montana.

Uses

Early uses of hemlock in Alaska were limited to mine timbers, rough-sawn lumber, house logs, poles and pilings, railroad and mine ties and fuel wood. Since the 1950s, hemlock fibers have been use in the production of specialty dissolving pulp in Southeast Alaska and are among the finest of raw material for this use. Western hemlock is relatively hard and is among the stronger western softwoods. Uses today include framing, architectural members, trim, roof decking, laminating stock, moldings, structural lumber, and veneer for plywood. In comparison with other commonly known construction species, such as Douglas fir, the wood of western hemlock is moderately light in weight, moderately low in shock resistance, and has moderately large shrinkage. Western hemlock is almost tasteless and odorless when seasoned, making it especially well-suited for food containers.

Durability

Western hemlock lumber gives good service in construction, although it has little resistance to decay.

Preservation

Western hemlock is somewhat resistant to conventional preservative treatment. It can be pressure treated but is more effectively treated by a water diffusion process.

Working Properties

The wood has a fine, moderately even texture, is nonresinous, and is easily machined and worked. The wood is intermediate in nail holding ability and has a tendency to split when nailed. It is satisfactory with respect to being glued and in taking stains, polish, varnish and paint. The wood is easy to work in all hand and machine operations and has little dulling effect on cutting edges. A clean finish can generally be obtained if sharp tools are used and are honed free from wire edges. However, the wood must be supported at the tool exit to prevent chipping out. The wood has a tendency to chip bruising in planing which can be overcome by having an efficient cleanout system which keeps debris from building up in front of the cutter heads. The wood is readily sliced to a smooth silky finish which is advantageous for the manufacture of veneers and plywood. It has good density and fiber length which makes it the most desirable species for making quality pulp and paper.