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Impacts of Hemlock Woolly Adelgids

Project Full Title:

Impacts of a developing Hemlock Woolly Adelgid Invasion on West Michigan Forests

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Project Description:

Ottawa County is the epicenter of a developing invasion of Hemlock Woolly 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 (HCNP) in August 2017. Heavily infested hemlocks often decline and die in 4-10 years, and the demise of hemlocks (which are evergreens) will fundamentally alter the species composition of forest understories by allowing more light to penetrate to the forest floor. Even before the invasion by HWA, Eastern Hemlock showed signs of declining in much of the upper Midwest. The reasons for that decline are unclear, but herbivory on seedlings by deer and climate change are likely candidates. Censuses at four sites in Ottawa and Allegan Counties indicate the same decline, and field experiments since 2013 suggest that both factors may be important locally as well. We will continue our demographic studies and assess HWA establishment at several sites in Ottawa and Allegan County to determine: a) whether hemlock was declining in our area even before the arrival of HWA, and if so what the major drivers of that decline were, b) how fast the HWA infestation is spreading at the HCNP, and how fast and how severely it is likely to affect hemlock populations in our area. This work will provide critical baseline data with which the HWA infestation in West Michigan can be monitored into the future, as it continues to spread within and among sites. Students involved in this project will spend a lot of time in the field, and will become familiar with both field instrumentation such as GPS and analytical tools like geographic information systems and statistical analysis with SPSS and the R programming environment. This project is open only to Hope College students.

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