Tsuga heterophylla, the western hemlock or western hemlock-spruce, is a species of hemlock. It typically grows to tall and is long-lived at high elevations. Native to the northwest coast of North America, it is a source of timber, tannin, and edible cambium.
Description
Western hemlock is a large evergreen conifer growing to tall, exceptionally , and with a trunk diameter of up to . It is the largest species of hemlock, with the next largest (T. mertensiana or mountain hemlock) reaching a maximum height of . Western hemlock's bark is brown, thin, and furrowed (outwardly appearing similar to that of Douglas-fir). The crown is a very neat broad conic shape in young trees with a strongly drooping lead shoot, and becomes cylindrical in older trees, which 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 appear on trees over about 25 years old; The species is closely associated with temperate rainforests, and most of its range is less than from the Pacific Ocean. Valleys it can be found in usually receive at least of rain annually. Older forests are damaged by rot-causing fungi, dwarf mistletoe, and leaf-consuming insects such as Acleris gloverana and Lambdina fiscellaria.
It can also be found in large gardens in northwest Europe and southern New Zealand.
Uses
Food and medicine
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 natives of Southeast Alaska. The inner bark was eaten by some Native American tribes as an emergency food, and the bark was cooked to make medicinal extracts for tuberculosis, rheumatic fever, and hemorrhage. has been used traditionally in the Northwest Coast.
Other uses
The bark has long served as a source of tannin for tanning leather. Its fiber is used to make rayon and various plastics.