Tuesday, May 8, 2012

Eastern Hemlocks

Eastern Hemlocks -- © Dave Spier

Of all the trees in New York, the Eastern or Canadian Hemlock (Tsuga canadensis) is probably my favorite. In old growth forests it is capable of living more than half a millennium. It’s a chief component of the climax forests found in the Adirondacks (generally at lower elevations below 2500'), the Catskills, the Lake Ontario shoreline, bog edges, the glens of the Finger Lakes Region and down across the Allegheny Plateau and Appalachian Mountains. In Pennsylvania, it is the state tree.

Eastern Hemlocks occur naturally from Wisconsin and Michigan eastward to the Canadian Maritimes and south through New England and the Mid-Atlantic states to the Appalachians of Tennessee and North Carolina where it is under attack by the wooly adelgid bug. When we re-visited Shenandoah National Park, it was sad to see the mighty groves of old-growth hemlocks reduced to skeletons and dead logs.

Laricobius nigrinus beetles, which are native to the Pacific Northwest, prey on the hemlock wooly adelgid, but I have not kept up on efforts to use them in the fight against the infestation. Cornell was involved with a test in the Finger Lakes region, where the problem is still minor. Cold winters work against the adelgid, but global warming could change that.

At their northern limit, hemlocks can grow at sea level, but the farther south one travels, the higher its preferred elevation. It is essentially a cool-climate evergreen that does better in areas with extra moisture or humidity. Annual precipitation ranges from 30 inches in the north to 60 inches in the south.

Like the Sugar Maple and American Beech, the hemlock grows well in the shade of other trees and, like its associates, it can reach heights of 100 feet. Under the right conditions, it has reached a record height of 173 feet in the South. The trunk of old trees can reach a diameter of five feet at chest height, and the record is six feet. The bark is dark brown and rough, often fissured with age, and was once a source of tannin used in tanning leather. The lumber was used for railroad ties.

For a tree that can grow to such large size, its cones are remarkably tiny and may barely reach an inch in length. Its needles also are small. Unlike pines and spruces, hemlock "needles" are flat, rounded at the tips and they line both sides of the flexible twigs. This is an advantage in shedding snow before the twigs and branchlets break. The undersides of the needles are whitened with two stomatal bands that allow the exchange of gases with the air. The half-inch long needles are attached to twigs by slender stalks, unlike Balsam Fir needles which are flat but attach directly with circular bases. The needles of all conifers can be used to make a tea rich in vitamin C.

The undersides of hemlock needles -- © Dave Spier

Incidentally, hemlocks make poor Christmas trees because the needles fall as soon as they dry. It’s best to leave them growing because the seeds and needles provide food for Ruffed Grouse and twigs are eaten by deer, Red Squirrels and even cottontail rabbits.

In early spring, before the deciduous trees leaf out, the hemlocks add a welcome touch of green along with mosses, a few evergreen ferns and Skunk-cabbage leaves. On a clear morning, enjoy the sunlight streaming through the evergreens.

Questions, additions and corrections may be sent to The Northeast Naturalist.  There is a discussion of hemlocks in Michael Kudish's book, Adirondack Upland Flora.

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