Eastern Hemlock

Eastern hemlock, not to be confused with the poisonous carrot herb of Socrates' fame, is a shade-tolerant member of the pine family. Tsuga, the genus to which it is assigned, means "hemlock" in the Japanese tongue. In the cool coves of the Appalachian Mountains, hemlock is found in uneven-aged stands, both pure and mixed with white pine and hardwoods. There it inhabits all but the upper slopes, where it is replaced by Carolina hemlock, a handsome specimen with needles described by the Latin species name taxus, meaning the foliage extends as spokes on a wheel from all sides of the twigs. Ranges of the two species overlap.

Hemlock often occurs in groves, these groups expanding concentrically from where initial seed trees were earlier established. Other times, isolated stands are found, as on the Warrior Plateau of Alabama. While localized high humidity is attributed to these woodlands, hemlock trees may actually contribute moisture to the air, for evaporation anometers placed in these shady conifer forests in summer have shown water lost from the forested atmosphere to be only one-half of that lost in adjacent oak and pine stands.10

Although eastern hemlock trees may survive when stands are regenerated in full sunlight, optimum conditions require partial shade. For this species, either selection harvests—producing uneven-aged stands or shelterwood cuttings—providing for a single-aged forest are suggested. In any event, the canopy shade should not be reduced below 50%. An even-aged hemlock stand, however, appears uneven-aged because of the wide array of size classes present in these woods.

After establishment, this conifer grows more slowly than its competing broadleaf trees, making cleanings (silvicultural cuttings) of the latter necessary as often as several times during a rotation. Hemlocks respond well to release, probably partly because of the availability of additional soil moisture for the residual stems. Openings, by cleaning or thinning, must not be so severe that sunscald results, care needing to be exercised especially on south-facing slopes. The malady is serious on advanced reproduction where forests are suddenly and drastically opened.

Fire must be kept out of these woodlands. The thin bark makes even the mildest prescribed fire an unsound silvicultural practice.

A disjunct stand (now inundated by Lake Lanier) in the Georgia Piedmont grew 20 miles south of the nearest hemlock trees and the furthest south the species occurred naturally. The stand developed because of subsurface seepage in the biotite schist and gneiss rocks found beneath the soil. This took place on a north-facing slope, where heating and drying effects are minimized. Flooding of the site by the seepage removed litter, bared the seedbed, and deposited a thin layer of sand. As the high water receded, the soil remained moist and, with seeds periodically available, gave rise in time to a three-age forest.11

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