Thu. Dec 7th, 2023
Woolly Hemlock Adelgid: The Tree Killer

Have you ever walked along a sunny forest trail and found yourself in a shady grove of trees? One of those special places where the noise of the world is silenced?

You have entered an Eastern Hemlocks outpost.

Eastern hemlock bark.Bark of an older tree, with thickened scales divided into ridges.

Our tall, graceful hemlock trees are quite different from the poisonous plant species Socrates made famous.

Rather than being a symbol of death, eastern hemlocks better embody the resilience of life: while they grow slowly, eastern hemlocks can survive for 200 years in the shade of their shorter-lived tree cousins, waiting for an opportunity under the sun.

If they reach adulthood, eastern hemlocks can live more than 600 years. There are trees in our parks that still contain carbon in the rings of trees grown before 1615, when Samuel de Champlain arrived at Lake Huron with the help of the Wendat and Algonquin peoples.

Under threat, again

Slow-growing eastern hemlocks have been recovering in our forests for several decades, but sadly they are once again threatened. These trees may not represent death, but they risk suffering from it.

He Hemlock woolly adelgid is an invasive insect that is killing eastern hemlock trees in Nova Scotia and the eastern United States. It has been found in the Niagara region of Ontario.

The Canadian Food Inspection Agency recently identified an area in Grafton and is working to delineate the current finding and will work to improve survey efforts in 2023.

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So far, the outbreaks in Ontario have been successfully controlled, but If left untreated, woolly hemlock Adelgid kills most, if not all, of the trees it infests.

The underside of an eastern hemlock branch.Photo: Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station, To see if a tree is infested with Woolly Hemlock Adelgid, examine the undersides of Eastern Hemlock branches.

Why are eastern hemlocks important?

Ample habitat for everyone

Sucker holes in an eastern hemlock trunk.Sucker holes in an eastern hemlock trunk. Saapsuckers drill holes in distinctive horizontal rows

Eastern hemlock forests are islands of habitat for the black-headed warbler and hermit thrush. Hemlock trunks are a favorite sap source for yellow-bellied sapsuckers and ruby-throated hummingbirds that pass by to feed on sap from pre-drilled holes.

Dense branches provide shelter to white-tailed deer, which often choose these areas as a roosting spot, and hemlock bark is a favorite of the porcupine.

Many fungi form associations with the roots of eastern hemlock, exchanging sugars for soil nutrients.

The presence of eastern hemlock makes the entire forest stronger and more resilient.

Eastern Hemlock Tree Shelter.Dense branches protect from wind and snow.

Important for our history.

These trees are also culturally important.

The leaves, branches and bark have long provided medicine to indigenous people.

The distribution of hemlock forests influenced the settlement of settlers in areas east of Georgian Bay; Bracebridge and Parry Sound were historically tannery towns, relying heavily on tannin-rich hemlock bark.

More recently, large quantities of Ontario spruce were used to build the Toronto subway tunnels in the 1950s and 1960s.

Take Steps to Protect Eastern Hemlocks

Ecologists and foresters are working to limit the spread of this tree killer, but they don’t have a complete map of where eastern hemlocks live in Ontario.

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Eastern Hemlock Needles.From above, the needles are bright green. From below, they look whitish, with two distinct white lines on each needle.

You can help by adding eastern hemlock sightings to iNaturalist. Look for trees that have:

  • flat evergreen needles that are dark green on top with two white lines below
  • scaly bark when young, becoming deeply furrowed and dark brown with age
  • small cones (1.5-2 cm) that grow downward and remain on the branches until spring
  • drooping branch tips and an overall feathery appearance

Eastern hemlock cones.Look for trees that have small cones that grow toward the ground.

You can find more photos here and more information about the Hemlock Woolly Adelgid from the Invasive Species Center. If you think you have found a tree infected with adelgids, report it on EDDMaps so invasive species experts can take action.

The next time you find yourself in a shady stand of eastern hemlock, thank them for their service to both humans and the ecological integrity of Ontario. Take a photo for iNaturalist and help protect our forests for many years to come.