Location: Just east of the Alaska Yellow Cedar east of the Burke Museum parking lot, west of Memorial Way NE.

Summary: Another tree of the high elevations, this species helps define the upper elevational limits of forests from Alaska in the north all the way to the Sierra Nevada Mountains of California in the south. A relative of the Western Hemlock, (which is more commonly spotted in the lower elevations). Mountain Hemlocks exhibit several key differences in appearance compared to their more well-known lowland cousin. For one, the needles of Tsuga mertensiana jut out from twigs in every angle in what is commonly referred to as a “bottlebrush” pattern of growth. High mountain forests are usually less dense, which means sunlight can be captured from all directions around the branch. Western Hemlock, by comparison, usually has leaves which emerge off to either side of the twig to maximize the capture of sunlight trickling in from above in the denser forests of low elevations. Sunlight in Mountain Hemlock territory is in fact so abundant that these leaves require extra protection from the damaging rays. The blue-ish green tint of T. mertensiana leaves is caused by the presence of a waxy cuticle (protective layer) and numerous stomata, which together act a bit like a natural sunscreen. Another trait of this tree tailored for life in the high mountains, these hemlocks are remarkably flexible, able to bear the crushing weight of snow year after year, sometimes spreading into a twisted shrubby bush known as a krumholtz (which means “twisted wood” in German). Life with short growing seasons requires great longevity to reach any substantial size. Some Mountain Hemlock in the Mt. Baker area have grown to a size of only a few feet in diameter, yet an inspection of their annual growth rings reveals that they are over 700 years old.

The presence of this tree in high mountains makes it more inaccessible to humans, however, there is still a fair amount of documented human use including for the traditional production of medicines for treating tuberculosis, hemorrhage, and rheumatic fever, as well as the more utilitarian use of the boughs as a soft surface for sleeping upon. The species has also been harvested for timber, though not nearly as much as the Western Hemlock.

The Mountain Hemlock is surpassed in tolerance for high elevations by perhaps only three other species of tree in our state, the Alpine Larch, Whitebark Pine, and Subalpine Fir. It is notable, however, that these three other species are absent from campus, their specialized adaptations reducing their tolerance for the warm conditions and long growing seasons of the lowlands.

Identifying Features light: The Mountain Hemlock shares a somewhat similar appearance to its lowland relative the Western Hemlock, a graceful swooping form, short irregularly sized needles, and thick furrowed reddish-brown bark. It differs in key respects, including the orientation of its needles, which grow in a bottlebrush manner from all sides of the twig. The foliage color too is different, a pale blue-green which is immensely pleasant to look upon and results from the trees stomatal bands, lines of tiny holes in the leaves which plants use to exchange gas and water with the atmosphere to power photosynthesis. The cones of the mountain hemlock are distinctly larger than those of the Western hemlock, growing 2-3.5” in length. They are a purplish to yellow-green color with woody yet readily pliable scales rounded on the ends. Often the leader on the tree, that is the topmost branch of the trunk, may be seen drooping over gently like a cresting wave. Often limbs will extend all the way to the ground even on ancient trees of this species. As suggested by the name, a final way to distinguish the species is by location. The mountain hemlock grows at higher elevations in mountainous terrain compared to the Western hemlock.

Identifying Features In Depth:

1. Form: It must be noted that the form of this tree may vary significantly based on location within its range. In extreme environments such as at timberline or in its northernmost extent in Alaska or where exposure is severe, the Mountain Hemlock may take the form of a creeping bush, with a blunt spreading shape low to the ground creeping over the terrain. When conditions are favorable, however, it may take a completely different and more stereotypical shape, with a tapering trunk and conical crown of horizontal to drooping branches achieving a height of 30-100’ (9-30m) and above and a diameter of 1-3’ or greater. It is on these model specimens where one might see the distinctive drooping leader, which is particularly slender and long and obvious from some distance.

2. Leaves: Needles are evergreen and variable in length, spreading on all sides of the twig in a bottlebrush pattern (when looking straight at the branch they appear much like a star shape). They are often slightly curved upwards and 0.25-1” (0.6-2.5cm) in length, a light bluish green. They are blunt tipped and stout and white stomatal bands appear on both sides of the needle.

3. Bark: Bark is apparent even on younger specimens, and is gray to deep brown. With age it becomes even thicker and deeply furrowed into scaly ridges. Twigs are likewise brown to reddish in color, and often slightly hairy.

4. Reproductive Bodies: Cones are longer than those of the Western hemlock, 1-3” (2.5-7.5cm) in length with round tipped scales and long-winged seeds. They are purplish when young and turn brown when mature, handing down from the branches with no stalks. Seeds are paired.

Native Range: This species may be found from the Sierra Nevada of California north to Prince William Sound in Alaska, growing from about 5,500 up to and sometimes exceeding 11,000 feet in elevation in the southern extent of their range and from sea level up to 3,500 feet in Alaska. It may be found inland only in a small region of Idaho and Montana up the Rocky Mountains into Southern Canada.

Historical Background: This tree is of ecological significance in that it occupies the subalpine zone just below timberline. Wood has been used by indigenous people for tools, utensils, and carving, but the tree also serves value as a food source to species traditionally hunted in the Pacific Northwest, including deer and elk and even smaller species like the snowshoe hare. They also provide stability and a means for building up soils in high elevation locations. This is of immense benefit in an ecosystem when much of the substrate is but recently eroded from solid rock. Even when dead they provide substrate for new saplings to grow in.