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Saving Michigan’s Hemlock Trees: Our Fight Against the Hemlock Woolly Adelgid

By: Logan Yonkus and Emily Rhodes - Three Shores CISMA Crew Leaders



The eastern hemlock tree is an important yet vulnerable species in the state of Michigan. It’s valuable to our Michigan ecosystems because it keeps streams cool, prevents erosion, and provides shelter to various wildlife species. In recent years, the hemlock woolly adelgid (HWA) has found its way to Michigan, threatening the hemlock tree's health. HWA crawlers are very small and often hard to see, however in the winter they can be easily identified by the white woolly masses they form on the underside of the branches by the base of the needle. HWA feeds on the sap of the eastern hemlock tree severely depleting them from vital nutrients that they need to survive.


The Three Shores Cooperative Invasive Species Management Area (CISMA) is a non-profit organization assisting in invasive species management. A large focus for the CISMA the past few winters has been stopping the spread of HWA by conducting surveys and inspecting the underside of hemlock branches in Chippewa, Mackinac, and Luce counties. Currently, HWA resides in five Michigan counties: Allegan, Ottawa, Muskegon, Oceana, and Mason. “If HWA is in one of our counties, it is our job to find it,” says Emily Rhodes, one of the Three Shores CISMA hemlock surveyors, “This is a statewide effort, CISMAS across Michigan are actively seeking and treating infestations to reduce the spread of HWA”. HWA was first brought to the states from japan around the 1950s, however, infestations have only been recorded in Michigan in the 21st century.



Underside of an eastern hemlock tree with topside in background
Underside of an Eastern hemlock tree


HWA can be dispersed in many ways. Often it is carried by birds and other forest creatures, which unfortunately we have no control over. However, much of the spread is caused by people too; by knowing the basics our community can slow the spread of HWA tremendously. Not moving firewood long distances, buying hemlock trees from responsible nurseries, and parking away from nearby hemlock branches in case of possible infestations are a few ways individuals can prevent HWA from spreading. Taking these precautions will help preserve Michigan’s hemlock trees and protect entire forest communities.



Three Shores CISMA surveying a hemlock grove near St. Ignace, Michigan


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