The Cook Forest Conservancy obtained permission from the author to link to this informative article, which summarizes the situation, the current science, and the programs and trials underway in the US to control HWA (hemlock woolly adelgid, an invasive insect) on Eastern Hemlocks, as of late 2020. Cook Forest State Park is a priority area for HWA treatment, as both an exemplary old-growth area, and a National Natural Landmark – so our trees are in better shape than most. HWA is currently in the forest, though, and we and all others in hemlock forests must remain informed and vigilant.
Hope for hemlocks: New tactics found to fight deadly pest
by Ad Crable for the Bay Journal, 23 November 2020
The article bluntly sets forth the magnitude of the threat:
“Without intervention, most trees in natural settings will die,” according to [Pennsylvania’s] latest Eastern Hemlock Conservation Plan.
There still are an estimated 124 million hemlock trees greater than five inches in diameter alive in Pennsylvania. But that’s nearly 13 million fewer than in 2004, and the mortality rate has increased fourfold since 1989.
and emphasizes the importance of Eastern hemlock to hundreds of other species, and its unique and irreplaceable niche in the forest ecosystem. For example, Hemlock groves provide cooling, filtering, and erosion control along streambanks, and their survival is essential for the survival of native trout, and the other organisms of Pennsylvania’s cold water streams.
The article succinctly covers the current methods of protecting hemlocks, from injecting chemical pesticides into the soil surrounding tree roots, to releasing varieties of beetles and sliver flies that predate on the HWA. Scientists are studying stands of hemlock which appear resistant to HWA, and working on replicating this characteristic.
Science is working to help the hemlocks find a natural balance – to let the tree adapt to this non-native insect threat, or to bring in predators of HWA to keep its impact on hemlock health manageable – and to keep this valuable and venerable conifer in our forests. Because, as Donald Eggen, forest health supervisor for the Pennsylvania Bureau of Forestry so aptly states:
When you walk through a hemlock forest, you are experiencing a unique habitat that is only found in a hemlock forest.