The Eastern hemlock (Tsuga canadensis) is a tree native to Frederick County that is usually found in cooler, damp areas that mimic its preferred northern forest habitat. The range of eastern hemlock extends along the Appalachian Mountain chain, the lake states, and throughout Canada. There are two species of hemlocks native to the east: the Eastern Hemlock and Carolina Hemlock.
Hemlocks are native to the United States and northern Asia. They are slow growing trees that can germinate and develop in shady conditions. These “shade tolerant” trees are often an important component of older growth forests where they grow alongside beech, sugar maple, white pine, yellow birch, basswood, and oak trees. Hemlocks can develop in dense groves where little grows beneath the shady conditions of their understory. These trees can grow large and live a long time. One of the largest hemlocks ever measured was 160 feet tall, had an 8 foot diameter, and was 988 years old. An insect known as the hemlock woolly adelgid has severely impacted hemlock stands throughout the eastern part of its range. This insect attaches to the smaller twigs and needles to suck the juices of the tree, causing the general defoliation and death of this evergreen within 3-7 years.
During periods of hot, dry weather the weakened hemlocks can also be attacked by mites and hemlock scale insects which accelerate their demise. Many of the hemlock groves that have sheltered cold water trout streams in our county have declined to the point that water temperatures in these streams are beginning to rise, to the detriment of the trout populations.
There is an active program nationwide to restore hemlocks to their native range by controlling the adelgid with insecticides or introducing beetles that feed on them, by manipulating the forest to encourage hemlock growth, and by replanting strains of hemlock that are resistant to the adelgid.
Just recently (autumn 2015,) a strain of Eastern hemlock known as “bullet proof” was planted in a study plot in Cunningham Falls State Park to ascertain whether or not this particular strain will be resistant to the hemlock woolly adelgid infestations. The bullet proof strain was planted with native hemlocks and some nursery-raised hemlocks as part of the study. Periodic observations and measurements will be taken to see if the bullet proof strain is more resistant than the other strains that were planted alongside. If the bullet proof strain displays pronounced natural resistance to the pest, it could be used to reestablish hemlocks in other areas.
Article by FCFCDB
Nature Note for 1/24/2016