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Tsuga mertensiana, known as mountain hemlock, is a species of Tsuga native to the west coast of North America, found between Southcentral Alaska and south-central California.
The conifer cone are small (but much longer than those of any other species of hemlock), pendulous, cylindrical, long and broad when closed, opening to broad, superficially somewhat like a small spruce cone. They have thin, flexible scales long. The immature cones are dark purple (rarely green), maturing red–brown 5 to 7 months after pollination. The are red–brown, long, with a slender, -long pale pink–brown wing.
Best development of mountain hemlock is on loose, coarse-textured, well-drained soils with adequate moisture, and in British Columbia, on thick and very acidic organic matter and decayed wood. Adequate soil moisture appears to be especially important in California and Montana, where summer drought is most pronounced.
Mountain hemlock will grow on most , but individuals typically develop best in mixed stands of forest on sheltered slopes or in draws. From southern British Columbia south, the tree grows better on northerly exposures. The preference for relatively moist, cool sites evidently becomes a necessity as the climate becomes more continental in western Montana and more mediterranean in the central Sierra Nevada at these extremes of its range. In these locations, mountain hemlock typically grows in isolated populations in north-facing glens and cirque basins where snow collects and may remain well into summer.
Mountain hemlock is adapted to sites with long-lasting . In the spring, mountain hemlocks emerging through of snow were transpiring, whereas nearby did not transpire until the soil beneath them was free of snow. Mountain hemlock is well adapted to cope with heavy Crown snow-load, with tough branches and the drooping branchlets shedding snow readily.
Mountain hemlock is Shade tolerance and other forms of competition. It is more shade-tolerant than all of its associates except Pacific silver fir, western hemlock, and Alaska cedar. Mountain hemlock is considered a minor climax species on most of its habitats, and pioneers on glacial moraines in British Columbia and Alaska. In many communities of the mountain hemlock forest in British Columbia and Washington and northern Oregon, Pacific silver fir is a major climax species. Alaska cedar, western redcedar, and western hemlock are climax associates on some sites. Mountain hemlock is more commonly the major climax species in the mountain hemlock zone south of central Oregon where Pacific silver fir does not occur.
Mountain hemlock often succeeds lodgepole pine or subalpine fir when these species pioneer on drier sites. It also tends to replace Engelmann spruce when the two species occur together, possibly because hemlock is better able to withstand the allelopathic effects of spruce than are other associated species.
The species is attacked by the root rot Phellinus weirii. Stands lost to fire can be populated by lodgepole pine, which is in turn succeeded by mountain hemlock.
Since the mid-20th century, the species has been used for lumber, often mixed with western hemlock.
Several have been selected, mainly for intensely glaucous foliage color including:
Uses
Native Americans used the species less often than western hemlock, but specifically used mountain hemlock boughs as beds and bathing brushes.
Cultivation
Outside of its native range, mountain hemlock is grown as an ornamental tree. It is planted as a specimen tree in native plant in California, and particularly in in northern Great Britain and Scandinavia, where it is appreciated for its blue–green color and tolerance of severe weather. Cultivation is limited by the very slow growth of young plants and its susceptibility to urban air pollution.
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