Eastern Hemlock

The Eastern Hemlock (Tsuga Canadensis) is sometimes called Canada Hemlock and Spruce Pine and is found throughout Pennsylvania. There are still old-growth hemlock stands that are remnants of the original forest that covered the Northeast before European settlers arrived. The hemlock was so prominent, it was named Pennsylvania’s state tree. In 1896, the “Father of Pennsylvania Forestry,” Dr. Joseph T. Rothrock, stated, “If Pennsylvania were to select one tree as characteristic of our state, nothing would be better than the hemlock.” The Pennsylvania legislature designated Eastern Hemlock the official state tree on June 22, 1931.

Hemlocks are medium-sized to large evergreen trees, ranging from 10–60 m (33–197 feet) tall. The bark is scaly and commonly deeply furrowed, with the color ranging from grey to brown. The branches stem horizontally from the trunk and are usually arranged in flattened sprays that bend downward towards their tips. They thrive in cool, moist woodlands on ravines and along stream banks. Hemlocks prefer growing on north-facing slopes and usually grow singly or in small groups rather than forming extensive, pure stands.

There are ten hemlock species in North America and Asia. Four are found on this continent. No hemlocks are found in Europe. However, there is fossil evidence that they were once there.

Two Eastern North American species are under serious threat from a sap sucking insect, the Hemlock Woolly Adelgid. The adelgid was first seen on the West Coast of North America in the early 1900’s. It was perhaps accidentally introduced from trees and shrubs imported from Eastern Asia.

Western hemlock species showed some resistance to the adelgid. However, the Eastern Hemlock has not fared so well. Millions of them can infest a single tree. The insects feed by sucking sap from the hemlock twigs. This causes the needles to die and fall prematurely. This combined with other environmental factors, such as drought, has cause mortality to be high. Some trees are able to survive an infestation if the adelgids die during a winter freeze or are washed away by rain. Scientists are studying potential natural controls with hopes of saving the hemlocks.

This is one of 11 (eleven) informational signs at Landis Woods Park.