Eastern Hemlock – Tsuga canadensis

Wetland Indicator Status: FACU

Pinaceae – Pine family

Eastern hemlock Tsuga canadensis Bark

Eastern hemlock (Tsuga canadensis) Bark

The Eastern Hemlock (Tsuga canadensis) is an interesting big old tree found throughout much of eastern North America.  It frequently occurs in wetlands, but is more often encountered in upland habitat.  It is a long-lived, slow-growing, very shade tolerant tree.  It can live decades under the shade of its parent tree, barely growing year after year for a century.  In this way an Eastern Hemlock tree is biding its time waiting for whatever is shading it to die, fall and leave a hole in the canopy.  Most Eastern Hemlock seedlings won’t make it far they will just perish in the shade.   However a few lucky ones will see a hole open up and then the tree will kicks its growth into high gear and reach for the light before any other nearby trees do the same.  Once up in the canopy growth slows again and if conditions are favorable the tree will spend the next few centuries shading out other saplings that are waiting for it to die.

The Eastern Hemlock was largely passed over by loggers looking for the much more marketable Eastern White Pine in the late nineteenth century because of the poor quality of its lumber.  However, many of the stands of Hemlock were destroyed in the great fires after the logging days.  The logging left tons of branches, and dead unmarketable trees on the ground, which became a great fire hazard and burned in tremendous forest fires.  Untouched groves of hemlock were often killed because although the trees have fire resistant bark their shallow, often partly exposed roots do not.   Today we find most of the ancient hemlocks in the shadows of natural fire breaks like lakes and rivers, and that is not altogether very different then they were found in the pre-logging days.

Eastern Hemlock grove

Eastern Hemlock grove in winter.

Eastern hemlocks brittle wood is sometimes used in construction, boxes and pulpwood, but is not sought after.  While hemlock wood has never had much commercial value its bark is high in tannin and was used in the leather tanning industry.  Many big old trees were felled only for their bark.

Eastern Hemlock rings

Cross section of a small Eastern Hemlock (Tsuga canadensis) showing growth rings and healing after the death of a large section of vascular tissue.

Groves of Eastern Hemlock often contain few or no other species of tree because of the deep shade they cast.  In addition the build up and slow decay of their needles makes the soil very acidic, leaching away nutrients and minerals.  The thick canopy of needles catches much snow and provides something of a refuge for animals from the heavy snows of winter.  The seedling and saplings of Eastern Hemlock also provide winter browse for white-tailed deer.



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