In most of its range mountain hemlock (Tsuga mertensiana) defines the upper portion of subalpine forests. Its elevation is variable and depends on latitude with the trees in Alaska ranging from sea level to 3,500 feet, while in the Southern Sierra Nevada mountain hemlock grows at approximately 9,000 to 10,000 feet in elevation. Mountain hemlock’s distribution is British Columbia, Alaska, Washington, Oregon, California, Idaho, Montana and Nevada where it is associated with long winters and deep snow-pack.
The growth form of mountain hemlock depends on habitat. Trees grown in open areas are tall, single-stemmed and erect with a conical crown and branches extending to the ground. On exposed ridges and near the tree line, this majestic tree assumes a prostrate, shrubby form. Whatever the form, mountain hemlock is long-lived, shallow-rooted and easily killed by fire.
Mountain hemlock bark varies from reddish brown to charcoal grey. The bark is deeply fissured and scaly. Twigs are yellow-brown and pubescent. The main branchlets have side branches.
The needles (leaves) of mountain hemlock spread in all directions from the twig and in that way the tree resembles a spruce, or even a fir, more than other hemlocks. The needles are rounded, not flat, blunt tipped and have small, distinct stems. Stomata on the needles give them a lighter green color.
The seed cones of mountain hemlock fully mature in one season. Long and cylindrical, the pendulous cones are purple, ripening to brown or grey with age. Mountain hemlock produce their first seed cones at about 20 years of age.
Rarely used for commercial purposes, mountain hemlock wood is fine grained, weak and soft.
Black hemlock and hemlock spruce are other colloquial names for T. mertensiana. The genus name, Tsuga, is from two Japanese kanji, “tsu” and “ga” meaning “tree” and “mother”. My daughter, who lives in Japan, confirms that tsuga in Japanese is translated as hemlock or spruce. The German botanist, Franz Karl Mertens (1764 – 1831) is honored by the species designation.
These mountain hemlock specimens were growing along the Discovery Trail at Crater Lake National Park (Klamath County OR).