An inviting shelter of deep shade and clear ground in any season, the serene space beneath a patch of hemlocks is a favourite spot at many cottages. The tall, graceful evergreens, most often growing on thin, moist, rocky soil along lakeshores and north-facing hillsides, are also vital sanctuaries for birds and beasts in the deep freeze of winter. No other tree, in fact, shelters a greater variety of wildlife, though hemlock makes up only a small part of central Ontario’s mixed forest.
Made for the shade
Eastern hemlocks persist longer in less sunlight than just about any other tree. Happily taking root in the shadow of others, they grow very slowly. Apparent saplings only a few centimetres thick can be 200 years old. When a big tree falls and opens up a hole in the overstory, such patient, stunted old-timers can suddenly shoot up with youthful vigour, rising dozens of centimetres in a year and potentially living on for centuries.
A deep, dense canopy of widespread, flexible limbs allows such scant light through that little else grows on the soft, thick mat of needle-fall beneath a hemlock. The canopy also keeps most snowfall from reaching the ground below. Deer, which bog down in snow deeper than half a metre, often congregate in scattered clumps of 15 to 20 hemlocks connected by corridors of more singly spaced hemlocks. These “deer yards” provide easy movement and a microclimate several degrees warmer than the surrounding hardwoods, and the herbivores relish the hemlocks’ lower twigs and seedlings.
Moose and snowshoe hares also eagerly browse on hemlock. Higher up, ruffed grouse hop from branch to branch sampling buds and needles, while porcupines are known to remain ensconced in a single tree for days at a time, nibbling on the inner bark of the upper branches. Even the tree’s interior can be occupied, with the base of a very large, old, hollow hemlock a favourite winter den for bears. Tiny, light-brown, winged seeds rain down through the winter, the oil-rich flakes feeding many mouths, from red squirrels and mice to chickadees, juncos, pine siskins, and wild turkeys, especially when big cone crops come every two to three years. Bumper crops also bring white-winged crossbills, nomadic boreal birds that use their specialized beaks to pry seeds from cones before they fall.
Limits of tolerance
Despite its ability to hold back the winter, hemlock cannot endure the extremes of the boreal forest. It peters out north of Sudbury, the Soo, and a narrow belt along the US border in northwestern Ontario.