Eastern Hemlock

Eastern Hemlock -- Tsuga canadensis -- has very specific and stringent requirements for regeneration. Human influence works against these requirements from being realized and consequently the Eastern Hemlock is in decline.

Old growth hemlock forests were once prevalent in central and eastern Ontario. Indeed much of the City of Ottawa was once hemlock forest. But while an undisturbed hemlock forest, as part of a mature forest, is stable and will not be succeeded, a hemlock forest is very susceptible to disturbance by man. To regenerate, a hemlock forest requires a cool moist environment, deep shade, exposed rich and moist mineral soil without leaf litter, and the absence of browsing ungulates. Periodic surface fires and mature surrounding forests producing an environment unfavorable to whitetailed deer are probably necessary.

The specificity of these requirements has the consequence that as Hemlocks are harvested they are not regenerated and thus the Hemlock forests are being irretrievably lost. Even in Algonquin Park, much of the "original" old growth hemlock forest is gone forever. While there may be preservation of the remaining stands, without regeneration, these will eventually succumb.

There seems little economic incentive to preserve the Eastern Hemlock.

Bat Lake Trail  hemlock cathedral grove

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Walking through the hemlock grove along the Bat Lake Trail in Algonquin Park. The deep shade and lack of underbrush are typical of hemlock forests, although this grove has been opened somewhat by the wind storms of the summer of 2006.

Bat Lake Trail  small hemlocks

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Small, but not necessarily young, hemlocks along the Bat Lake Trail in Algonquin Park. Note the feathery appearance and the drooping leader (see comments by Pielou below).

notes

According to John Farrar, in Trees in Canada:

Hemlocks occur in the temperate parts of North America and Eastern Asia. Worldwide about 10 species are recognized; of the 4 species native to North America, 3 are found in Canada: western hemlock and mountain hemlock in British Columbia, [and] eastern hemlock from Lake Superior to Cape Breton Island.

...

[The eastern hemlock] grows on various types of soil, but requires a cool moist site; found in pure stands or mixed with yellow birch, eastern white pine, red spruce, white spruce, sugar maple and American beech. Very shade tolerant; small trees persist in closed stands for many decades.

Used for coarse lumber. Separation between the annual rings ("ring shake") and along radial lines ("star shake") often occurs in living trees, resulting in lumber that is subject to splitting and brittleness. Knots in the lumber are hard enough to dull a saw or deflect a nail. Not suitable for camp fires because the burning wood throws off sparks.

The bark was formally used as a commercial source of tannin, and many bare logs were left in the woods.

In discussing the return of vegetation following the retreat of the last ice age E.C. Pielou states that:

It turns out that each species has a unique migratory history ... It is believed that the eastern white pine and the eastern hemlock survived the Wisconsin glaciation in a refugium in the eastern foothills of the Appalachians and the adjacent coastal plain.

... eastern hemlock began its northern migration about 1000 years later than the eastern white pine, presumably for ecological reasons. Eastern white pine can succeed on poor, dry soils, exposed to full daylight, but eastern hemlock requires a richer, moister soil and the shade of other trees. Therefore, conditions did not become suitable for the advance of hemlock until generations of plants had lived, died, decayed and enriched the soil, and a forest of other trees had developed to to provide shade.

With respect to identification, in The World of Northern Evergreens E.C. Pielou states that:

A hemlock is most easily recognized by standing back and looking at the tree as a whole. It is far more graceful and lacey and feathery, than the other conifers. The reason is that the leaves are small and the outer ends of the branches are slender, flexible, and drooping. The most unmistakable characteristic of a hemlock is its dangling leader. The leader (leading shoot) is the upermost part of the stem of a tree, above all the side branches.

The leader of a young hemlock is pliable, and curves over to give the tree a graceful, nodding tip. In an old tree, the graceful curve usually becomes an angular twist or bend. Each leaf tapers at the base to a short, slender stalk that makes a sharp angle with the leafs midrib. The leaves are a variety of different lengths -- anywhere from 0.5 to 2 cm -- all mixed together. The leafless twigs, though not smooth, are not nearly so rough as spruce twigs.

As a quick recognition tip, John Laird Farrar in Trees in Canada says:

Distinguished from all eastern native conifers by its slender twigs and oblique leading shoot.

In Wolf Country, John Theberge writes:

Uncut, undefiled old-growth hemlock stands are north-country cathedrals. Graceful limbs, bowing branches, fluted trunks. Tiers of delicate dark-green archways filter the sunlight like a stained-glass window.

Hemlock logs lying on the forest floor, the skeletons of generations past, decompose slowly because of their tannin- and resin- embalmed trunks. Among the logs grow shade loving goldthread, the pale flowers of wood sorrel, flushes of red moccasin flowers. Blackburnian warblers nest here, repeating their thin, upwelling notes from the hemlock spires. Sapsuckers embroider the trunks with neatly aligned holes. Few places are more enchanted.

Hemlock stands such as these are cut down, even in a park, to make wharf pilings, railway ties, and little wooded crates used to store and ship commercially grown mushrooms. In the past hemlock bark provided tannin to cure leather. Once prominent in pre-crosscut saw, pre-chain saw Ontario, we have succeed in breaking the back of this species. No longer does golden hemlock pollen float great distances on the spring breeze. Indeed, only a little is wafted into the air, too often searching in vain for a reproductive partner.

...

From a technical standpoint, the problem is that you cannot cut more than about 30 per cent of a hemlock stand without flooding the forest floor with too much light for these shade-loving seedlings to grow. However, to allow seeds to germinate you need to scarify the ground, scrape away the deep accumulation of needles so the tiny seeds can reach mineral soil. Fire does tis naturally, but fire is fought and extinguished almost everywhere. Alternatively, you can scarify the soil with a bulldozer, but it is difficult to drive one around if you have cut so few trees.

Theberge also wrote, quoting one of his graduate students' results:

... hemlock stands were the most heavily used forest type, per hectare, by wintering moose in Algonquin Park. Moose find shallow snow and shelter from the cold winds there, and can wander out into the surrounding hardwood forests to browse, an ideal arrangement.

Dan Strickland writes in the Booth's Rock Trail guide:

At the same time, the cover-providing hemlocks, so important for the winter survival of deer, have diminished in the Park. While we now preserve the hemlock stands which are used frequently as winter deer yards, many other stands were cut earlier and they are not easily regenerated. Deer themselves are fond of browsing on young hemlocks -- the very trees which could in the future provide vital winter cover for their descendants.

Dan Strickland also writes in a Raven article, Murder in the Cathedral:

... More or less pure patches of Hemlock are a fairly regular hilltop feature in the hardwoods of the Park's west side. These groves are important not only because they are a distinct and beautiful element to our eyes in what would be an unbroken sea of Sugar Maples but also because, being very different little islands of conifers among the hardwoods, they contribute to the diversity and richness of Park wildlife. When you walk into a hemlock grove, for example, you immediately leave the Red-eyed Vireos and Least Flycatchers behind and start hearing the songs of blackburnian and Black-throated Green Warblers. Or, if you visit in the evenings, you may be serenaded by a Swainson's Thrush -- a bird you would never expect to find in the hardwoods just a hundred yards away.

Hemlocks are important for larger animals as well. On cold winter nights, the temperature can be several degrees warmer under a hemlock stand than out in the surrounding leafless hardwoods. White-tailed Deer, often pushed to the limits of tolerance here at the northern edge of their range, are quick to take advantage of such slightly warmer temperatures by preferentially bedding down under the cover of hemlocks. Deer also find that travel is easier in groves of hemlocks because ... there is noticeably less [snow] accumulation on the ground below. ... deer often "yard up" in such places for the winter.

[In pretty well any hemlock stand in Algonquin Park], there are few young hemlock trees beneath the old ones. Although you may well see see the odd seedling-sized individuals, even these are usually very old. One forester once found a tree just 10 inches in diameter that was 359 years old, and even a two-inch tree may be as much as 200 years old. ... a recent thorough search in one area failed to find a hemlock less than a century old.

... One factor may well be the small size of the seeds. They are so tiny that when they germinate, the little roots are incapable of penetrating the layer of dead leaves on the forest floor and the hemlock seedlings never get established. Even if they do manage somehow, they root so shallowly that they may very well succumb to drought when the top inch of soil dries out in the would-be tree's first summer ...

But even if a crop of hemlock seedlings does get established and survives the first few summers to the point where the plants are robust enough to withstand drought, none of this may account for much if there are any deer around ... deer love hemlock foliage so much that a few of them can move into a grove and totally wipe out any seedlings ... The fact that we actually have hemlock stands, incidentally, is a pretty strong suggestion that deer must have been very rare, if not totally absent, in the old Algonquin forests of centuries ago when our present hemlocks got started in life.

In Trees of Algonquin Park Dan Strickland wrote:

... When Hemlock itself is cut, however, it is rarely succeeded by other Hemlocks and many large areas in northern Haliburton and adjoining southwestern Algonquin lost all their Hemlocks around the turn of the century when the bark of these trees (in particular, its tannin content) was in heavy demand for tanning leather. A further blow ... came with extensive logging in the Park for Hemlock in the 1950s and 60s (the Toronto subway was built with Algonquin Hemlock shoring timbers, for example) and many authorities believe this was a major contributor to the demise of deer in the Park. Today, under the Algonquin Park Master Plan, the cutting of Hemlocks and other conifers is carefully controlled in the parks remaining deer yards.

Sources

John Laird Farrar (1995), Trees in Canada, Fitzhenry and Whiteside Limited and The Canadian Forest Service, Natural Resources, Canada.

E.C. Pielou (1988), The World of Northern Evergreens, Comstock Publishing Associates (Cornell University Press).

E.C. Pielou (1991), After the Ice Age, The Return of Life to Glaciated North America, University of Chicago Press.

Dan Strickland (1991), Murder in the Cathedral, reprinted in The Best of the Raven, The Friends of Algonquin Park.

Dan Strickland (1994), Booth's Rock Trail, Man and the Algonquin Environment, The Friends of Algonquin Park.

Dan Strickland (1991), The Trees of Algonquin Park, The Friends of Algonquin Park.

Theberge, John B. with Mary T. Theberge (1998), Wolf Country, Eleven Years Tracking the Algonquin Wolves, McClelland & Stewart Inc.