Tsuga canadensis – Eastern Hemlock

When the wind lifts up the Hemlock’s voice, it is no roaring like the Pine’s, no keening like the Spruce’s.  The Hemlock whistles softly to itself.  It raises its long, limber boughs and lets them drop again with a sigh, not sorrowful, but letting fall tranquility upon us.

– Donald Culross Peattie, A Natural History of Trees of Eastern and Central North America

Double white band on the underside of Hemlock needles.

There’s something about Hemlock that is reminiscent of the large California coastal redwoods:  the broad, conical crown, the cinnamon brown furrowed bark, the graceful tiers of feathery branches.  But our Eastern Hemlock lies in the Pine Family, not the Cypress family, and although substantial does not reach the giant proportion of the temperate climate Sequoias.

Hemlock has shiny, flat, warm-green needles, 10 to 15 mm long that extend outward from densely layered branches.  The dark density of a Hemlock forest is brightened by two wide white bands that extend the length of each needle’s underside, reflecting and shimmering light into Cimmerian gloom.  Its red-brown, sometimes purple-brown trunk often contains rows of tiny holes drilled by Yellow-bellied Sapsuckers seeking sugar.

Hemlock is sometimes confused with Balsam Fir (Abies balsamea) as the flat needles on both trees have two light-coloured bands underneath and are arranged in a single plane pointing forward on the twig.  But there are many obvious differences between these trees.

Trees Canadensis:  Cinnamon brown Eastern Hemlock bark at Gillies Grove in Arnprior.
Cinnamon brown Hemlock bark at Gillies Grove in Arnprior.
  • Needle size – Fir needles are two to three times longer than Hemlock and usually not as dense in number along the twig.
  • Twigs are alternate on Hemlock versus opposite on Fir.
  • Bark – Hemlock bark is brown, cinnamon brown or even purple brown at maturity, vertically oriented in plates or furrows and similar to mature White Pine bark. Balsam Fir bark is grey, somewhat smooth often with raised blisters that when pressed will express resin.
  • Seed cone size and attachment – Hemlock seed cones are small (10-15 mm) and pendant, hanging near the tips of branches and turning from closed and green to warm brown as they ripen and open in early fall. Fir cones are erect, oblong, and 25 to 50 mm long turning purple to brown when they mature.

When in doubt gently crush the needles between your fingers; an aromatic Christmas-tree fragrance indicates Balsam Fir.

Trees Canadensis: Hemlock, White Pine, and Eastern White Cedar share a nurse stump.
Hemlock, White Pine, and Eastern White Cedar share a nurse stump.

The presence of Hemlock signifies a climax forest where rotting nurse logs provide a preferred germination substrate. They are often found on rocky, cool, north-facing slopes where the tree can reach its roots down into reliable moisture. Waiting for windfall to open up a sunny glade, it grows slowly in the shade of other trees, meaning the age of a mature Hemlock is likely greater than its size would indicate. In Eastern Ontario, the largest reach 30m high and about one meter DBH.

Hemlock shares its forest with Yellow Birch (Betula alleghaniensis), Beech (Fagus grandifolia), Red Spruce (Picea rubens), and White Pine (Pinus strobus). The small Hemlock and Yellow Birch seeds need clear ground or a nurse log to be successful as their roots cannot penetrate duff so they are often found in close, physical association.

Trees Canadensis:  Yellow Birch and Eastern Hemlock at Shaw Woods.
Yellow Birch and Hemlock at Shaw Woods.

According to historical records, Hemlock and White Pine were the dominant trees in the Ottawa Valley and both were logged extensively.  But only the thick bark at the bottom of the old growth Hemlock trees was used for its high tannin content in curing leather; the rest of the tree was discarded as waste.

Finding a healthy regenerating forest of Hemlock is becoming rare.  The tree is under threat from climate change, deer, and a foreign pest.  Hot dry summers with extended drought stress the trees.  Expoding White-Tailed Deer populations decimate seedlings.  Woolly Adelgid, an introduced Asian aphid-like insect that is moving into Ontario, kills the tree by feeding at the base of its needles, depriving it of nutrients. The Eastern Hemlock Project in iNaturalist is tracking the spread of Hemlock Woolly Adelgid (Adelges tsugae), which is most easily observed from March through June as white, cottony egg sacks in the needles at the terminal end of branches. HWA is native to western Canada, but eastern hemlocks have no defence against it.  Migrating birds heading north in the spring are spreading the pest from the northeastern US into eastern Canada.

Hemlock’s preference for cool, moist, undisturbed interior forest conditions means it’s now more prevalent outside of Ottawa. Large, mature trees can be found at Gillies Grove, Blakeney Rapids, Shaw Woods, the Riverside Trail (Almonte), and Gatineau Park.  Within City of Ottawa boundaries you can find large specimens in the greenbelt at Bell Centennial Woods and Alan Gordon Acadian Forest, and at Trillium Woods along Shirley’s Brook by the bridge, Billberry Creek in Orleans, and in Fitzroy Provincial Park.

Here are selected photographs with location coordinates in iNaturalist:

https://www.inaturalist.org/observations/8513519 – shows Hemlock and Balsam Fir side by side.

https://www.inaturalist.org/observations/8449656– young green cones.

https://www.inaturalist.org/observations/5458016 – old growth hemlock at Gillies Grove.

https://www.inaturalist.org/observations/3202405 – buds.

https://www.inaturalist.org/observations/9953144 – 100 foot Hemlock in Lanark County.

https://www.inaturalist.org/observations/9953731 – mature bark in Lanark County.

https://www.inaturalist.org/observations/9922186 – one of many large Hemlock at Bell Centennial Forest.

Trees Canadensis:  Large Eastern Hemlock (Tsuga canadensis) at the Alan Gordon Acadian Forest.
Large Hemlock at Alan Gordon Acadian Forest.
Trees Canadensis:  Eastern Hemlocks (Tsuga condenses) at Blakeney Rapids.
Hemlocks at Blakeney Rapids