Characteristics of Mountain Hemlock Tree (Tsuga mertensiana) in the Wild

Tsuga mertensiana
Mountain hemlock (Tsuga mertensiana) is a species of hemlock of the genus Tsuga that is native to the west coast of North America, with a northwestern boundary in the Kenai Peninsula, Alaska, and a southeastern boundary in northern Tulare County, California.

The tree’s Latin name refers to Karl Heinrich Mertens (1796-1830), a German botanist who collected the first specimens as a member of the Russian expedition of 1826-1829.

The geographic range of mountain hemlock is fairly similar to that of Tsuga heterophylla (commonly called “western hemlock”), also being mostly less than 100 km from the Pacific Ocean apart from similar inland populations in the Rocky Mountains of southeastern British Columbia, northern Idaho, and western Montana. The inland population most likely formed after deglaciation by the extraordinary long-distance dispersal of more than 200 km of the coastal population. Their range, however, differs in California, where western hemlock is limited to the Coast Ranges and mountain hemlock is found in the Klamath Mountains and Sierra Nevada.

Unlike western hemlock, mountain hemlock mostly grows at an altitude of 1,000 m asl, in Alaska, 1,600-2,300 m asl, in the Cascades in Oregon and Sierra Nevada 2,500-3,050 m asl.

Mountain hemlock is usually found growing naturally in cold, snowy subalpine sites where it grows slowly, sometimes reaching over 800 years of age. Arborescent individuals possessing narrow conical crowns into old age (300 to 400 years) and
shrubby krummholz in cool, windy locations near wood paths add to the beauty of the mountainous landscape.

Areas occupied by mountain hemlocks generally have a mild to cool marine climate that includes mild to cold winters, short growing seasons, warm to cold, and moderate to high rainfall.

Mountain hemlock thrives best on loose, coarse-textured, well-drained soil with adequate moisture. In British Columbia, mountain hemlock grows on thick, highly acidic organic matter and weathered wood. Adequate soil moisture appears to be especially important in California and Montana, where summer drought is most pronounced.


Characteristics of Mountain Hemlock Leaf

Tsuga mertensiana Leaf
Source: Fischer

The leaves are needle-shaped, 7-25 mm long and 1-1.5 mm wide, soft, blunt-tipped, pale turquoise above, and with two broad bands of bluish-white stomata below with only a narrow green midrib between the bands. The leaves are arranged spirally around the shoot.

The shoots are orange-brown, with a dense pubescence of about 1 mm.


Characteristics of Mountain Hemlock Fruit

Tsuga mertensiana Fruit
Source: Tree Library

Conical, small, pendulous, cylindrical, 30-80 mm long, and 8-10 mm wide. Immature cones are dark purple (rarely green) when ripe red-brown within 5-7 months after pollination. The seeds are red-brown, 2-3 mm wide and 7-12 mm long, pale, pink-brown wings.


Characteristics of Mountain Hemlock Tree

Tsuga mertensiana Tree

Mountain hemlock is a large evergreen coniferous tree that grows to a height of 35-40 meters, with the tallest specimens up to 60 meters and the lowest trunks up to 2 meters in diameter. The bark is thin, gray, and cracked or wrinkled.

The crown of the tree is neat, slender, conical on young trees with sloping or drooping shoots, becoming cylindrical on older trees. At any age, it is distinguished by slightly pendulous ends of the branches.

Mountain hemlocks will grow in most landscapes, but individuals usually thrive best in mixed forest stands on sheltered slopes or ledges. Mountain hemlocks are also tolerant of shade and other forms of competition.

Mountain hemlock adapts well to heavy snow and ice loads, with hard, drooping branches that shed snow easily.

Outside of its native range, mountain hemlock is grown as an ornamental tree, specimen in the landscape, and bonsai. This tree is highly valued in the north of Great Britain and Scandinavia, for its blue-green color and tolerance for inclement weather.

Several cultivars have been selected, particularly for their very glossy foliage color including Tsuga mertensiana ‘Blue star’ and Tsuga mertensiana ‘Glauka’.



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