By Tom Koritansky, Natural Resource Manager
The eastern hemlock (Tsuga canadensis) is an important component to the hemlock hardwood forests in Ohio. Hemlock hardwood forest is a common forest type along most of the ravines in the Grand River and Chagrin River watersheds in Lake County. They are important breeding areas for a number of state-listed breeding birds including red-breasted nuthatch, winter wren, hermit thrush, magnolia warbler, Blackburnian warbler, Canada warbler and dark-eyed junco (all “Special Interest”) as well as uncommon breeding birds like blue-headed vireo, black-throated green warbler and northern Parula warbler. There are also numerous species of insects dependent on this habitat.
At Penitentiary Glen Reservation in Kirtland, the eastern hemlock trees that line the gorge along Stony Brook are a staple of that unique ecosystem. This dense grove of hemlocks provides an abundance of shade that keeps the water cool and capable of supporting organisms that need cool, moist environments to survive throughout the year like salamanders, fish and freshwater invertebrates. The roots of these trees are also pivotal in providing a stable streambank along the extremely steep terrain of the gorge.
Unfortunately, a few unwanted forest pests have emerged on the hemlocks at Penitentiary Glen within the past few years that now pose some threats to these special trees. Those unwanted guests include an armored scale insect known as the Elongate Hemlock Scale (Fiorinia externa), the Hemlock Wooly Adelgid (Adelges tsugae) and a fungus known as the Fabrella Needle Blight (Fabrella tsugae).
Hemlock wooly adelgid
The Elongate Hemlock Scale is a small insect that feeds on the undersides of hemlock needles and removes nutrients by piercing and sucking. Scales pose a serious threat to the hemlocks because as they multiply, they can reach levels that may cause trees to die. The Hemlock Wooly Adelgid attaches to the base of needles and in winter covers itself in a wool-like waxy coating to protect itself and its eggs. As adelgid infestations increase on a tree, mortality can occur within four to ten years. Fabrella Needle Blight causes a loss of needles on sections of branches. Symptoms are noted most during late July and August when needles of affected branches turn orange and then die.
Since these pathogens are proving to be problematic for the hemlocks at Penitentiary Glen, Lake Metroparks has taken steps to try to improve the health of these trees. During the winter of 2017-2018, Lake Metroparks’ staff conducted a thorough survey of the hemlocks that line the gorge. Trees were examined for the presence of the Elongate Hemlock Scale and the Hemlock Wooly Adelgid. After the survey and consultations with other natural resource professionals in Ohio to develop a course of action, Lake Metroparks began treating affected trees along the gorge to control the infestations. Unfortunately, no treatment exists for the Fabrella Needle Blight; however, lessening stress on the trees caused by the other pathogens may improve their chances of surviving the blight.
Assessments will take place again this winter to examine the effectiveness of treatments and to gauge how these pathogens have progressed throughout the year. Controlling these pests is an arduous task, but we remain hopeful that the control efforts will be successful and beneficial to the hemlocks at Penitentiary Glen Reservation.