A Visit to the Fabled Adelgid-Resistant Hemlock Grove

In October I took a roadtrip with my friend Cameron Wygent, a local mycologist and restoration ecologist, to a place I had only read about: a grove of adelgid-resistant eastern hemlocks, that may very well hold the key to the survival of the entire species.

The damp, shaded path into the heart of the grove

Eastern hemlock (Tsuga canadensis) is a native conifer stretching along the Appalachians from Nova Scotia to Georgia. In the past few decades, however, it has been brought to the brink of extinction by a tiny white insect called the Hemlock Woolly Adelgid. As with Dutch Elm Disease and the Chestnut Blight, the adelgid has wiped out entire hemlock-dominated forest ecosystems throughout Appalachia, leaving skeletons of the forests that once were.

Some of the trees are not resistant, and hemlock woolly adelgid is very much present at the site

But there is hope: in addition to vital research being done on predatory insects and pathogens that could curtail the hemlock woolly adelgid, forest ecologists have discovered a small number of hemlock groves throughout their native range that seem to be surviving due to a natural resistance to the infestation. Tucked away in a handful of peer-reviewed studies, we found mention of these "bulletproof" stands of eastern hemlock, and decided to see for ourselves if the claims were true.

The adelgid-resistant trees are lush and healthy, even when surrounded by dying non-resistant trees

After hours of driving, we left our car off the side of a muddy dirt path and hiked our way into the forest. Within a few minutes we entered something I never thought I would see in my life: a healthy grove of eastern hemlock trees. Their dark, glossy boughs cast a deep shade over native ferns, mosses, and orchids - a far cry from the dead and dying hemlocks we are accustomed to seeing throughout the rest of Appalachia. This was a truly sacred place - a natural repository of the genetics that could save this entire species from extinction. The adelgid is indeed present here, and there were some dying trees that did not have a natural resistance, but the deeper we walked into the grove, the shadier and greener it became, and we knew we had entered the heart of the grove. Studies have shown that the resistant trees in this grove have higher levels of terpenes - aromatic compounds that are natural insect repellents that are common among conifers (think of the smell of crushed pine needles, for example). These same terpenes have also been shown to be beneficial to human health, and are central to the practice of "Forest Bathing" in Japan.

Dark, glossy foliage on a resistant tree. Elevated levels of terpenes may be what allow this tree to repel infestation

We are grateful to the scientists doing work with these trees, and we hope that these genetics can soon be utilized in breeding adelgid-resistant hemlocks for planting across Appalachia. These trees are foundational in their importance to these ecosystems, and in a time filled with daily news of ecological catastrophe and extinction, it is comforting to know that there is, indeed, hope for the endangered hemlock forests of Appalachia.

Cameron with an unexpected find: an Elaphomyces false truffle that’s been parasitized by a Cordyceps mushroom