You can help eastern hemlocks!
Interested in volunteering? This page consolidates information found throughout the site to provide you the details you need to get started. Visit our Events Calendar to view upcoming training sessions.
What are eastern hemlocks and why are they important?
The eastern hemlock (Tsuga canadensis) is a foundation species in the areas of the Northeast forest where it is found. It provides vital ecosystem services that benefit humans and wildlife. If it is removed from the landscape, the effects can be devastating to other species and costly to remediate.
The eastern hemlock is a slow-growing coniferous tree with an attractive, lacy crown that can reach up to 175 feet tall. Hemlocks can live over 900 years.
Hemlock trees prefer cool, moist sites and are often found along streams, lakes, and on the steep slopes of gorges. Their shallow roots make them vulnerable to drought stress and windthrow.
Hemlocks fulfill a variety of essential ecosystem roles, making them a necessary component of a healthy landscape. They provide food and shelter for wildlife across the landscape, and they protect and filter water sources that are valuable to animals and humans alike.
Deer, porcupine, grouse, squirrel, and mice all eat hemlock, especially during the winter when other food sources may be scarce. Hemlock groves also provide excellent sources of cover because of their dense canopy and open understory.
The cool shade created by the overhead canopy provides a sanctuary during the hot summer months and keeps snow from melting rapidly during spring thaw, creating a slow steady influx of water into streams and lakes. Hemlock shade directly over streams is also important for maintaining the temperatures necessary for many aquatic species, including native brook trout.
Hemlocks make up much of the forest cover along shorelines and streams, and are key for preventing erosion and filtering out pollutants. New York City and other cities in the state rely on the hemlocks surrounding reservoirs and lakes to keep municipal water supplies clean.
How to identify a hemlock tree
Not sure you can identify an eastern hemlock? The Arbor Day Foundation’s What tree is that? can help with some easy guided questions. The Brandeis Conifer Field Guide allows you to view selected species side-by-side as you learn to differentiate them. For auditory learners, Cornell’s ForestConnect has a great dendrology crash-course video to help you identify and understand the ecology of Northeast conifers.
What is hemlock woolly adelgid (HWA)?
The hemlock woolly adelgid (Adelges tsugae) is an aphid-like insect native to Asia that has devastated hemlock populations in the eastern United States. It was first discovered in the US and established as a pest in the 1950’s. HWA is easily recognized by white woolly egg sacs, which can be found on twigs in late winter through early summer. Once hatched, adelgids attach to the twigs near the base of the needles and feed on the tree’s sap. An infestation can slow or prevent the tree’s growth, eventually resulting in the death of the tree over the course of several seasons.
Why is HWA a threat?
HWA has caused widespread mortality in eastern and Carolina hemlock populations in the United States due to a lack of predators and low resistance among the trees. This drastic decline in hemlocks poses a problem for forest composition, as many species of wildlife rely on hemlocks for food and shelter. It also may cause a decrease in water quality for human drinking water supplies.
Where is HWA in New York?
HWA has moved through southern and western New York. It has not yet been discovered in the Adirondacks. Click here to view a time-lapse map from the New York State Department of Environmental Conservation showing the spread of HWA in New York since 1985. Originally, it was hoped that cold winters would prevent HWA from spreading north or into the Adirondacks, but the insect has demonstrated resistance to cold. Even if there is a temperature limit to HWA’s range, it will continue to spread and cause widespread mortality among hemlock populations of New York unless effective identification, treatment and prevention protocols are adopted.
How can I look for new infestations?
Click here to view our HWA survey protocol.
The best way to look for new infestations is to visit sites with dense hemlock populations. Hemlocks prefer cool, moist sites and are often found in gorges and along lakefronts.
For an overview of hemlock populations in New York, click the map to the left.
Remember to be safe whenever you spend time in the forest!
Who do I coordinate with to incorporate HWA surveys into my outings?
Please contact the New York State Hemlock Initiative: NYShemlockinitiative@cornell.edu
How do I identify HWA?
First, take a few moments to look through our Volunteer Training Slideshow. This is a .pdf of a presentation, and there are “Comments” to help interpret the slides.
HWA can be detected any time of year, but it is easiest to look for egg sacs from winter through to early summer. Egg masses are typically found on twigs at the base of where the needles attach, and look like small woolly lumps. The most common items mistaken for HWA are spider egg sacs and spittlebugs. View lookalikes here.
If you are not sure whether you have found HWA, please take several good quality photos and send them to us at NYShemlockinitiative@cornell.edu.
How do I report HWA?
Please visit our Report HWA Finding page to learn about how to report HWA.
Where can I learn more about HWA?
Visit our Hemlock Woolly Adelgid page for links to more information.
Check our Events Calendar for upcoming public education events in your area.