Eastern Hemlock

Tsuga canadensis

by John Brouwer

Where should one plant a tree which has a life expectancy of 800 years?

Eastern hemlocks are among the older trees in the Carolinian forest. They generally reach maturity at 400 years and some live up to 1000 years. Hemlocks are conifers, having needles which stay on the tree year round. Hemlock needles are flat and grow off the stem in one plane.

Average tree height is 100 feet although some are recorded at 170 feet. Similarly average mature trunk diameter is 5 feet, though some reach 6 feet.

The largest Eastern Hemlock has been calculated to have 44.8 m³ of wood. This makes the hemlock the largest evergreen conifer. The larger eastern hemlocks are found in the southern Applachians.

Hemlock was very abundant in the northern-eastern USA and eastern Canada after the ice age but then underwent a sudden decline, almost disappearing from the pollen record around 5,000 years ago. It later returned, but never became as abundant as it had been previously. The causes of this 'hemlock decline' are unknown, but it is likely to have been due to some form of pest or disease.

As a long lived tree eastern hemlock has some particular growth characteristics. The tree is very shade tolerant. It can survive under only 5% of full sunlight. Germination requires constant cool and moist temperatures – conditions usually found only in old growth hemlock and associated forests. Trees developing under the canopy can survive in the shade for up to 400 years before a dying canopy tree provides it with the light to grow to maturity.

Because of the pervasive logging in eastern North America there are very few older specimens of eastern hemlock.

During the pioneer days most of the hemlock in southern Ontario and other parts of North America was harvested just for the tannin in the bark. The tannin was used in curing hides to make leather. Stands were cut, the bark was stripped and the rest of the wood was just left to rot in the forest.
Lumber production from eastern hemlock reached its peak between 1890 and 1910. Primary uses were in light framing, sheathing, roofing, subflooring, boxes, crates, and general millwork. Much of the present production is used in pulping or newsprint and wrapping papers.

Today stands of eastern hemlock continue to decline due to logging and the failure of hemlock to naturally regenerate. Because hemlock seed requires the unique conditions of a mature forest floor to germinate and grow, clear cutting precludes regeneration of the species. Selective logging would allow for natural seeding, but North American forestry operations have refused to use this approach.

Eastern Hemlock has been a popular landscaping tree. It is equally tolerant of full shade and full sun. Its textured droopy foliage, pyramidal growth habit and ability to withstand hard pruning makes it an attractive ornamental tree. A host of cultivars have been selected, providing landscapers with types ranging from hedge to free-standing trees. Eastern Hemlock has been spared the infamy of Christmas trees as its needles tend to shed rapidly after it is cut.

In the forest the flat needles and droopy branches hold a lot of snow. This makes it important to wildlife, especially White-tailed deer. White tailed deer will gather in large groups in an area of dense evergreen trees when extreme cold and deep snow threaten their survival. These areas are known as deer yards. The canopies formed by evergreens, particularly stands containing a high proportion of Eastern hemlock, intercept as much as sixty percent of each snowfall, providing an insulating blanket overhead with an area of shallow snow beneath. Deer within the yard all use the same trails, which become packed, providing easier walking conditions.

The canopies also shelter many other animals and birds. Many animals, including deer, graze the hemlock foliage when other vegetation is not available.

Two insects introduced from Asia, the woolly adelgid and elongate hemlock scale are threatening the eastern hemlock forest of the New England states. Infected trees die within ten to fifteen years. Winter cold has limited the northern range of these insects but there is concern that climate change will allow the insects to range into southern Quebec and Ontario.

In 399 BC Socrates was tried and convicted by the courts of Athens on a charge of corrupting the youth and disbelieving in the ancestral gods. His execution by drinking hemlock was documented by his student Plato. And this gives hemlock trees a bad rep.

However in English, 'hemlock' also refers also to poison hemlock which is an herb member of the Umbelliferas plant family, a large grouping which also includes edible vegetables as carrots, celery, dill, parsley, and parsnips. In Europe it is easy for hemlock herbs to be mistaken for these vegetables with dire results. However there is no relationship to the hemlock tree.

Where should one plant a tree which can live for 800 years? Two years ago three eastern hemlock seedlings were planted in the co-op in the area between block two and the road. It will be up to future generations of co-opers to determine if these trees can coexist with co-op life through the next mellinium.

January 2009