Our forest is home to more than 1,000 Eastern hemlocks (Tsuga canadensis), some of which appear to be 300-400 years old. Eastern hemlock is a foundation species in the Northeast, providing habitat that supports a huge diversity of other species. However, this vital tree is severely threatened by the invasive hemlock woolly adelgid, Adelges tsugae (or “HWA”). HWA is a destructive aphid-like insect introduced from southern Japan to the Richmond, Virginia, area in the early 1900s. Since that time, HWA has killed untold millions of hemlocks as it has spread through the forests of eastern North America.
Eastern hemlock is the third most common tree species in New York. Hemlock trees tower to heights of more than 100 feet and can reach ages of more than 700 years. Their evergreen canopies cast deep shade, which creates cool and dark microclimates for delicate native plant communities and nearby aquatic species. The great void left by the loss of the hemlock will be filled by deciduous forest throughout the Hudson Valley and greater Northeastern region, resulting in an entirely different ecosystem.
We are working with Cornell University’s New York State Hemlock Initiative (NYSHI) to implement the most aggressive hemlock research and protection efforts on private land anywhere in the United States. To date, we have chemically treated every hemlock we have found on the property (completed in 2023), GPS tagged each tree over 6 inches in diameter, and given each uniquely identified tree a health metric so we can monitor its health. We plan to re-treat every tree on a five-year interval to keep HWA numbers suppressed.
We have collected cones from the 10 healthiest hemlock trees on the property (that is, trees that have HWA infestation but continue to score high health metrics) and are working with a specialized grower to propagate seeds from these trees. Our goal is to identify and propagate hemlock trees with genetic resistance to HWA that we can use in our own onsite restoration efforts and also make available as a resource for others.
Since the introduction of HWA to eastern North America, no effective native natural enemies of the insect have been found. This prompted the initiation of a classical biological control program, with predators imported from Japan and from western North America, where some adelgids are native and under effective biocontrol. NYSHI has been one of the leading labs in the country working on implementation of HWA biocontrol.
At the Land Stewards demonstration site, we have started growing young hemlocks in a controlled nursery environment to support HWA predator experiments by providing young hemlocks with easily accessed branches. In 2026, we plan to infest these young trees with HWA deliberately, and then in 2027, we will work with NYSHI to introduce HWA predators into this controlled environment and into our native hemlock grove. To date, most biocontrol research has taken place on public lands like state forests and parks, and ours will be the first such research conducted on private land in New York.
Ultimately, we aim to help scientists develop the knowledge and tools necessary to protect the irreplaceable hemlock and to educate and inspire other private landowners to do their part in protecting these precious trees and all the benefits the confer to our wildlife and our lands.