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Impacts of Hemlock Wooly Adelgids

Project Full Title:

Impacts of a developing Hemlock Wooly Adelgid Invasion on Understory Plant and Litter Arthropod Communities in West Michigan Dune Forests

Project Mentor(s):

Muilenburg,Vanessa; Winnett-Murray,Kathy

Project Mentor(s) EMail:;

Project Start Date:


Project End Date:


Project Description:

Ottawa County is the epicenter of a developing invasion of Hemlock Wooly Adelgid (HWA), an exotic aphid-like insect that has already decimated populations of Eastern Hemlock trees in the eastern U.S. and promises to do the same in Michigan. Introduced to the U.S. in1951, the insect was discovered in the Holland area in 2015 and at the Hope College Nature Preserve in August 2017. Heavily infested hemlocks often decline and die in 4-10 years. Because the understory beneath Eastern Hemlock canopies constitutes a distinctly different microenvironment than that beneath broadleaved trees, HWA-driven defoliation is likely to influence the recruitment and survivorship of tree seedlings on the forest floor. In addition, pronounced canopy defoliation and impacts on throughfall and leaf litter composition may affect communities of leaf litter arthropods beneath hemlock canopies. In turn, both plant species composition and litter decomposition rates may be altered in west Michigan dune forests.

We will assess hemlock condition and HWA establishment at several sites in Ottawa and Allegan County, and compare the density and composition of litter arthropod communities beneath hemlock and adjacent sugar maple canopies. We will also compare light environments, soil temperatures, seedling recruitment, and photosynthetic rates of woody seedlings beneath hemlock and sugar maple canopies throughout the entire growing season, since the effects of Eastern Hemlock on the understory light environment are most pronounced before broadleaved trees leaf out in the Spring. The proposed study will add to our understanding of how insect pests can exert major direct and indirect influences on forest ecosystems by altering the physical structure of the environment. This project is open to Hope College students only.

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