by Jake Tomlinson
Growing up hunting grouse in the hills of north-central Pennsylvania, I learned early that once we reached the hemlocks, we had to be ready to shoot. To this young hunter it seemed that there wasn’t a hemlock in all of northern Pennsylvania that didn’t offer an opportunity at a bird. The Eastern hemlock (Tsuga canadensis) is Pennsylvania’s state tree and plays an incredibly important role in forests throughout the Northeast.
This large conifer reaches heights of more than 100 feet and generally holds its branches to the ground, providing grouse and other wildlife with thick cover and buds to snack on. The Eastern hemlock’s form and tendency to grow in thick, densely stocked stands also make it an important riparian component, cooling headwater trout streams. Additionally, hemlock produces versatile lumber that’s helped to shape economies throughout its native range.
Eastern hemlock is native throughout Eastern North America, and its range overlaps very well with that of ruffed grouse. It’s one of the most shade-tolerant species and only germinates in mature stands, preferring moist soils and Northern climates. Hemlock is one of the largest and longest-lived trees in the forests where it grows. Its needles are usually about ½ inch long, flattened and have two distinct lines on their undersides. Its bark is dark brown to reddish and develops deep ridges and furrows as it ages.
Historically, hemlock was used primarily for its bark. The bark was removed and boiled down to aid in the process of tanning leather. At the turn of the 20th century, many hemlock stands were clearcut to provide enough bark for the leather industry. Hemlock has also been valuable for lumber, as it produces a soft, straight-grained wood that’s perfect for building. When dry, it’s almost impossible to pull nails out of this durable wood. Hemlock is also used for railroad ties and as a source of pulp for the paper industry.
This tree is threatened across much of its range by an introduced pest, the hemlock woolly adelgid. The woolly adelgid is a tiny bug that attaches itself at the bases of the needles, robbing the tree of nutrients and eventually killing it. Large infestations have wiped out hemlocks in parts of their range, with massive resources being spent to try to control the adelgids and save the remaining trees in infested areas. You can identify affected trees by observing the white waxy masses at the bases of their needles. The masses are actually egg sacs, and before each adult female completes its life cycle, it lays between 100 and 300 eggs. In the spring, larvae emerge from the egg masses and are able to spread on their own.
Hemlock woolly adelgid control has been difficult. Through the efforts of state and federal agencies, universities and nongovernmental organizations, several biological controls have been tested. Various levels of success have been observed, but this pest continues to threaten hemlock across the southern end of its range.
A second pest currently on the rise is elongate hemlock scale. Like the hemlock woolly adelgid, this hardy insect also attaches to the undersides of needles and siphons off valuable nutrients, eventually killing the tree. Often this insect can be found along with hemlock woolly adelgids on the same tree. Control has focused on both insecticide applications and biological controls.
Although the hemlock is in decline, it remains an important component of forests, especially in the northern extent of its range, where mortality from these insects has been less prevalent. Preservation of this species is important, as it provides numerous ecological services. With proper site selection and care hemlock, seedlings can be planted successfully. Very young bare root seedlings do well in moist riparian areas with dense canopy above. The seedlings will develop in the understory, providing thermal cover for wildlife. Consider planting a few on your property, or reach out to your local Ruffed Grouse Society & American Woodcock Society chapter to plan a project.
