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Tsuga canadensis (L.) Carr. Eastern hemlock

Developing seed cones at end of shoots in mid-summer

Habitat

Eastern hemlock sometimes occurs on well-drained sites in pure stands or groves, but more commonly is mixed with red spruce and balsam fir, and sometimes sugar maple, beech, yellow birch and eastern white pine. It tolerates shade well, so it has the ability to grow slowly in dense shade for decades. Trees may last for well over 400 years.

Leading shoot of a tree showing bent-over character and sylleptic branches along it

Form

When young, the dense crowns of eastern hemlock can be gracefully conical with slender flexible branches that turn down at their ends, but sometimes crowns are more bushy with many stems vying for leader status. Middle-aged trees have irregularly conical to rounded crowns, and old trees, ragged, irregular, rounded, crowns with several large branches. Leading shoots are always bent over to a greater or lesser extent. Trees may grow to heights of up to 30 m and to stem diameters of up to 100 cm. The stems are noticeably tapered on younger trees, but can become massively columnar on older trees.

Pollen cones in axils of leaves

Morphology

The leaves are evergreen, needle like, 5–15 mm long, flat, dark green above, paler green with two whitish bands where stomata occur below, blunt pointed, with slightly and finely toothed margins, and rounded bases that merge into short petioles. Each leaf is borne on a tiny leaf cushion which arises from a flattened ridge that runs down the shoot a little. Although all leaves are borne in spirals around the shoot, those on its upper surface are shortest, and the ones borne below, that spread out sideways, are the longest.

Along each new shoot of more than about 6 cm long, there are small side shoots, without bud scales at their bases, in axils of leaves. On the shorter new shoots, these sylleptic side shoots may comprise only a short stem, a few small leaves, and a terminal bud, but on longer new shoots, some of the sylleptic shoots in the central part can be up to 10 cm long and carry leaves all along their lengths. Such shoots add substantially to the density of the crowns. Because sylleptic shoots occupy many positions where, otherwise, lateral buds would have occurred, there are relatively few true lateral buds. Most buds occur at the ends of shoots. The buds are small, conical to round, and greenish brown. They develop late in the season and carry only a small amount of preformed content. When the new shoots grow out, much of their lengths are neoformed.

Seed cone open to release seeds

Pollen cones are borne along the undersides of weaker shoots, in axils of leaves. Seed cones hang, throughout their development, at the tips of shoots of moderate vigor, and are 12–20 mm long when they open to release seeds, starting in late October.

The bark is dark brown and scaly when young. It is thick and deeply furrowed, with dark greyish-brown, flat-topped, slightly scaly ridges when old. If pieces of bark are broken off, purple flecking will show in the broken surfaces.

Notes

The wood of eastern hemlock is liable to have splits in it, even when still standing in the tree. The splits can occur in the radial direction and around the annual rings. This tendency for splitting limits the wood’s usefulness, except as large-dimension lumber in general construction.

Bark of stem, 30 cm in diameter

Bark of stem, 90 cm in diameter

Because the bark has a high tannin content, eastern hemlock trees used to be cut for their bark. The tannin was used in the tanning of hides for leather.