Olympic Habitat Development Study
US FOREST SERVICE

 

Station 2 -
Western Hemlock
(Tsuga heterophylla)
Family Pinaceae

Western hemlock is a major tree species along the Pacific coast (northern California to southeast Alaska) and northern Rocky Mountains. It is the state tree of Washington.  It is characterized by a drooping tip and drooping branches as well as feathery sprays of short needles. Hemlock needles have a ragged look, showing mixed lengths averaging 0.5 - 2 cm0.2 - 0.8 inch long.  There are 2 fine lines on the underside of the needles (these are stomates which the tree uses in gas exchange).  The twigs are slender and display small pegs when the needles fall off.

Hemlock’s small cones are about 2 - 2.5 cm0.8 - 1.0 inch long; the tree produces large amounts of seed in most years. Almost 20 million per ha8.1 million per acre were produced one year in a stand in coastal Oregon but even higher values have been reported in Alaska. It produces light seed which can be blown more than 1.6 km1.0 mile in a strong wind.

Hemlock is very tolerant to shade and it can be found in the understory, midstory, or overstory of forest stands.  High shade tolerance means that seedlings can survive in a low light environment and also that branches in the shade will survive for many years or decades resulting in long crowns.

The density of hemlock crowns is very high. The foliage is so efficient at intercepting light that very little penetrates below the canopy in dense stands and such stands support very few understory plants. Young western hemlocks often grow on top of stumps and fallen trees (called “nurse logs”) or other organic substrates but the species also grows well on mineral soils.

Western hemlocks dominate the coastal ecosystems of the Pacific Northwest.  Early loggers often passed over hemlock stands as the tree’s wood was less valuable. The species is still less valuable than some of its tree associates, but it is widely harvested.  Hemlock wood is used in construction  due to its strength and nailing characteristics and is an important source of fiber for the pulp and paper industry.

Its tannin-rich bark has had many traditional applications for Native American tribes, from tanning leather to skin protection and dying basket materials and dip nets.  The wood is moderately heavy and durable and was used for making spoons, bowls, dip-net poles, spear shafts. Branches were used for bedding material. Western hemlock’s springtime cambium was also eaten by natives during food scarcity.


 

Young western hemlock growing on a nurse stump.
Hemlocks have needles of irregular lengths. Young western hemlock growing on a nurse stump. Bark on western hemlock is thin and platy.
Young western hemlock growing on a nurse stump.