Why Do Western Hemlocks Have Droopy Tops?
Western hemlock is one of the defining trees of the great temperate rainforests of the Pacific Northwest. Despite being the largest of all hemlocks – particularly big specimens may be more than 200 feet tall – the species is overshadowed (literally) by conifer associates like Douglas-fir, western red-cedar and Sitka spruce, among the very biggest of the world’s trees. But the hemlock still stands out, not least because of its characteristic drooping tip. Does this Spark an idea?
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Drooping Terminal Leader
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The sagging top, or terminal leader, of a western hemlock is not a sign of disease or malnourishment, but simply an aspect of the tree’s genetics. Indeed, many of its relatives in the hemlock genus, scattered across North America and Eurasia, show the same trait. These relatives include the mountain hemlock that shares much of the western hemlock’s geographic range, but is restricted to higher elevations; often, though, the pendant of a mountain hemlock is not so pronounced. The tips of the lateral branches on a western hemlock usually also sag.
Form
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The drooping nature of hemlock branches in general may help the trees slough off snow. Many species thrive in very snowy places, like the boreal woods favored by the eastern hemlock or, even more impressively, the high, treeline groves of mountain hemlock in the West. The lower forests supporting western hemlock in the maritime Northwest, exposed to the moderating influence of the nearby Pacific, may be snow-free most of the winter, however.
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Appearance
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The “shepherd’s-crook” summit of a western hemlock is one of its defining characteristics, along with the pendulous, feathery look of its branches. This delicacy stands out in mixed conifer stands of the Northwest. In a typical mid-elevation stand in the Cascade Range, for example, Douglas-fir trees will not only tower over surrounding hemlocks but also distinguish themselves with sharp crowns pointed skyward, as well as coarser, more ragged branches. The “weeping” profile of a western hemlock is somewhat similar to that of a young western red-cedar – which also sports pendulous arms – though the two species, commonly neighbors, are otherwise unalike. The gentle droop of the hemlock’s top contrasts even more sharply with the summits of certain Douglas-firs, Sitka spruces and red-cedars that soar above the surrounding treetops; these true giants, exposed to the battering of the region’s fierce winter storms, often have broken crowns with multiple leaders.
Shade Tolerance
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Western hemlocks are among the most shade-tolerant trees in their native range. They also cast a lot of shade with their densely packed little needles and tightly layered, swooping branches. As Stephen Whitney points out in “A Sierra Club Naturalist’s Guide to the Pacific Northwest,” the deep gloom of a mature Northwest coastal forest owes more to the understory ranks of western hemlock than the mammoth Douglas-firs or Sitka spruces that dominate the canopy. Many such forests are essentially absent of young Douglas-firs or spruces, which are more shade-intolerant and need openings as made by windfall or fire to prosper. Thus western hemlocks will gradually assume the dominant position in these communities as the canopy masters eventually die – unless ecological disturbance again provides a foothold for the hemlocks’ competitors.
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References
- The Canadian Encyclopedia: Hemlock
- A Sierra Club Naturalist's Guide to the Pacific Northwest; Stephen Whitney
- Northwest Trees; Stephen F. Arno and Ramona P. Hammerly
Resources
- Photo Credit Comstock/Comstock/Getty Images
