Hemlocks Saving Hemlocks
Finding Health in a Threatened Ecosystem
Editors’ Note: For a detailed history of hemlock in the Northeast region and a scientific review of its ecological role in our forests, as well as past and current threats, read Hemlock: A Forest Giant on the Edge, edited by David R. Foster with contributions from Harvard Forest scientists and others, and view several related short videos.
A promising coalition of partners working on hemlock trees, genetics, and forest ecology has come together to restore eastern hemlock forests. The partners are many: The Nature Conservancy, The New York State Hemlock Initiative, the Hemlock Restoration Initiative, and others. You might be able to help locate wild, pest-resistant hemlocks.
As the U.S. Forest Service describes, hemlock is a critically important species in eastern forests, and its future is gravely threatened. The ecosystem in which hemlocks reside would not simply be degraded by their loss; it would cease to exist. Hemlocks create distinctive light, soil, and water chemistry regimes that form a unique niche, providing habitat and food for over 1,000 forest species. When deciduous trees have not yet leafed out in the spring, hemlocks provide shade, keeping the streams they overshadow cool and slowing snowmelt throughout the watershed. Unfortunately, hemlocks throughout eastern North America are threatened by an invasive species, Adelges tsugae, or hemlock woolly adelgid (HWA). This aphid-like insect has killed hundreds of thousands of hemlock trees in eastern North America, and hundreds of millions more are at risk.
Healthy hemlock branchlet. Photo © Liz Thompson
Hemlock woolly adelgid. Photo © M. J. Raupp
The Nature Conservancy, in collaboration with the U.S. Forest Service, has launched an exciting new project, Trees in Peril. The project is working to develop pest-resistant individuals of elm, beech, and hemlock. The Lingering Hemlock Project, a subset of Trees in Peril, focuses on breeding native HWA-resistant hemlocks. Lingering Hemlock Project partners include academic institutions, nonprofit organizations, and government agencies from throughout the range of eastern and Carolina hemlock (Tsuga canadensis and T. caroliniana). To develop HWA resistance, first we need to find HWA tolerant and resistant trees in the wild. To do this, we need partners to help us find hemlocks that have survived HWA (even if they aren’t in pristine condition post-infection).
Approaches to finding surviving, or “lingering,” hemlocks will vary in different parts of eastern North America. In some places (mostly the southeastern United States), many of the hemlocks have already died. Any surviving hemlocks in these landscapes are of interest to us, so partners could be individual hikers or foresters. In areas where many hemlocks haven’t died yet (mostly northeastern North America), we need partners to establish and monitor ongoing changes in hemlock health. These partners could be land trusts, academic institutions, or similar organizations who are able to set up plots and monitor them annually for hemlock decline.
Nick Dietschler, researcher, and Bill Widrig, volunteer, with an old, healthy hemlock. Photo Courtesy New York State Hemlock Initiative
Our collaborators who do tree breeding will test possible “lingering” hemlocks found by our new partners for genetic resistance to HWA. Eventually, interbreeding partially resistant hemlocks can generate a diverse, resistant stock of native hemlocks to reseed lost hemlock forests. Working together, we at the Lingering Hemlock Project have the opportunity to restore eastern hemlock forests to their former glory.
If you think you might be the right person to search for lingering hemlocks, contact Olivia Hall at education@savehemlocksnc.org. If you would like to establish and monitor a hemlock health monitoring plot, contact Grace Haynes at gh447@cornell.edu. We hope you’ll join us in safeguarding tomorrow’s hemlock forests.
Grace Haynes serves Cornell University’s College of Agriculture and Life Sciences as a researcher and program extension aide.