Tsuga heterophylla, the western hemlock or western hemlock-spruce, is a species of hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Sonoma County, California.
Habitat
Tsuga heterophylla is an integral component of Pacific Northwest forests west of the Coast Ranges, where it is a climax species. It is also an important timber tree throughout the region, along with many of its large coniferous associates.
Description
Western hemlock is a large evergreenconiferous tree growing to tall, exceptionally, and with a trunk diameter of up to. It is the largest species of hemlock, with the next largest reaching a maximum of. The bark is brown, thin and furrowed. The crown is a very neat broad conic shape in young trees with a strongly drooping lead shoot, becoming cylindric in older trees; old trees may have no branches in the lowest. At all ages, it is readily distinguished by the pendulous branchlet tips. The shoots are very pale buff-brown, almost white, with pale pubescence about long. The leaves are needle-like, long and broad, strongly flattened in cross-section, with a finely serrated margin and a bluntly acute apex. They are mid to dark green above; the underside has two distinctive white bands of stomata with only a narrow green midrib between the bands. They are arranged spirally on the shoots but are twisted at the base to lie in two ranks on either side of the shoot. The cones are small, pendulous, slender cylindrical, long and broad when closed, opening to broad. They have 15–25 thin, flexible scales long. The immature cones are green, maturing gray-brown 5–7 months after pollination. The seeds are brown, long, with a slender, long pale brown wing.
Ecology
Western hemlock is closely associated with temperate rain forests, and most of its range is less than from the Pacific Ocean. There is however an inland population in the Columbia Mountains in southeast British Columbia, northern Idaho and western Montana. It mostly grows at low altitudes, from sea level to, but up to in the interior part of its range in Idaho. It is a very shade-tolerant tree; among associated species in the Pacific Northwest, it is matched or exceeded in shade tolerance only by Pacific yew and Pacific silver fir. Young plants typically grow up under the canopy of other conifers such as Sitka spruce or Douglas-fir, where they can persist for decades waiting to exploit a gap in the canopy. They eventually replace these conifers, which are relatively shade-intolerant, in climax forest. However, storms and wildfires will create larger openings in the forest where these other species can then regenerate. Initial growth is slow; one-year-old seedlings are commonly only tall, and two-year-old seedlings tall. Once established, saplings in full light may have an average growth rate of annually until they are tall, and in good conditions still annually when tall. The tallest specimen, tall, is in Prairie Creek Redwoods State Park, California. It is long-lived, with trees over 1200 years old known. Western hemlock forms ectomycorrhizal associations with some well-known edible fungi such as chanterelles. It is capable of associating with wood-decay fungi in addition to soil fungi; this enables its seedlings to survive on rotting stumps and logs.
Western hemlock is cultivated as an ornamental tree in gardens in its native habitats and along the U.S. Pacific Coast, where its best reliability is seen in wetter regions. In relatively dry areas, as at Victoria, British Columbia, it is exacting about soil conditions. It needs a high level of organic matter, in a moist, acidic soil. It is also cultivated in temperate regions worldwide. It has gained the Royal Horticultural Society's Award of Garden Merit.
Forestry
When planted well upon the banks along a river, western hemlock can help to reduce erosion. Outside of its native range, western hemlock is of importance in forestry, for timber and paper production, it is used for making doors, joinery and furniture. It can also be an ornamental tree in large gardens, in northwest Europe and southern New Zealand. It has naturalised in some parts of Great Britain and New Zealand, not so extensively as to be considered an invasive species, but an introduced species tree. such as nurse logs and cut stumps
Food
The edible cambium can be collected by scraping slabs of removed bark. The resulting shavings can be eaten immediately, or can be dried and pressed into bread, as was done by the Native Americans of southeastern Alaska. The bark also serves as a source of tannin for tanning. Tender new growth needles can be chewed directly or made into a bitter tea, rich in vitamin C. Western hemlock boughs are used to collect herring eggs during the spring spawn in southeast Alaska. The boughs provide an easily collectible surface for the eggs to attach to as well as providing a distinctive taste. This practice originates from traditional gathering methods used by Native Alaskans from southeast Alaska, specifically the Tlingit people.
