Eastern Hemlocks

SEEING THE FOREST THROUGH ITS TREES, part two: Tsuga canadensis

By Larry Ely

“Besides shade, the Hemlock loves rocks; it likes to straddle them with its ruddy roots, to crack them with its growing, to rub its knees against a great boulder” writes Donald Culross Peattie in 1948 in his published Natural History of Trees of Eastern and Central America.   I feel this single sentence from Peattie’s work captures the essence of our native hemlock tree. 

Hemlock trees are shade tolerant, meaning in forestry terms that they are able to grow and thrive in low sunlight under a canopy of their own species or of another. Mature hemlock stands can be found as late successional climax forests where site conditions are ideal for their growth.

As hemlock ages, its bark becomes more reddish brown or brownish gray with distinctive ridges or fissures.

Hemlock thrives in a shaded understory and eventually becomes the dominant tree on the site, often as a pure stand or as an inclusion in a hardwood or mixed wood stand. Even under the closed canopy of a mature hemlock forest, new hemlock seedlings germinate and grow into young saplings. Those saplings wait in the understory for as long as 400 years before their own dramatic growth spurt occurs after a disturbance. Young saplings under five feet tall might be 50 years old, and the average lifespan of a hemlock tree that reaches maturity is 250 to 400 years and even up to 800 years. The hemlock is the old man of our forests. 

Pure stands of hemlock are often found on steep slopes with poor soils, especially along streams running through deep gorges. Less accessible to loggers, such hemlock stands are able to reach a climax stage. In our more managed forests, hemlock is still found in patches and as isolated individual trees among more numerous mixed hardwoods and other softwoods.

Hemlock retains its short needles throughout the seasons and can be identified by the flat, short, shiny dark green needles with a pair of parallel white lines on the underside. Balsam fir with similar underside markings can be distinguished from hemlock by its distinct aromatic scent when the needles are crushed. 

The often drooping branches have a feathery or lace-like look. As hemlock ages, its bark becomes more reddish brown or brownish gray with distinctive ridges or fissures. Mature trees usually reach 60 to 70 feet in height with a normal trunk diameter of 1 to 2 feet, though some may span as high as 100 feet with a 3-foot diameter. 

Pure stands of hemlock are often found on steep slopes with poor soils, especially along streams running through deep gorges.

Hemlock is important to wildlife, especially to the Black-throated Green Warbler and the Blue-headed Vireo that depend on forests with a hemlock component. Deer and moose browse needles and new growth, and dense hemlock stands are relied upon for their winter cover. Many smaller mammals feed on the seeds of hemlock, and porcupines feed upon clipped branches that they drop from the canopy.

Recognizing these wildlife values, foresters tend to treat hemlock stands and hemlock inclusions carefully when planning harvests or other management practices on their forests. Those treatments usually include creating small canopy gaps of up to a quarter acre in both pure and mixed stands, replicating natural disturbances and providing more growing space for hemlock.

This is part of a continuing series looking at the life of the common trees in our Mahoosuc Mountain Region.

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Photo Credits: 

Hemlock Forest, Hemlock Bark by Larry Ely

Hemlock Growing from the Rock is from Bibliothèque de l'Université Laval   http://cdm22018.contentdm.oclc.org/cdm/ref/collection/Botanique/id/9720 licensed under the https://creativecommons.org/licenses/by-sa/4.0/deed.en license.