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Winter Survival of the Invasive Hemlock Woolly Adelgid

Eastern Hemlock (Tsuga canadensis) is a foundation species distributed throughout New England forests. It is commonly found in the understory and provides a unique habitat for a wide variety of vertebrate and arthropod species that rely on the tree for food, shelter, and reproduction. Eastern Hemlock is in decline due to two non-native pests, the Hemlock Woolly Adelgid (HWA, Adelges tsugae), and the Elongated Hemlock Scale (EHS, Fiorinia externa). Both HWA and EHS cause defoliation of the hemlock’s needles. These two pests are currently limited by minimum cold temperatures and are unable to sustain a population in the northern part of the Eastern Hemlocks range. The last 100 years have been the warmest in recorded history and temperatures are expected to continue to rise, this creates a general northward shift in species preferred habitat and has caused the spread of species that are limited by cold temperatures. In order to see the impacts of the two pests in western Massachusetts, 40 sites were sampled in the fall of 2008 and revisited in the fall of 2022. Observations of an altitudinal range expansion for both pests were noted. The 2008 infestation saw HWA at elevations of 135 meters, the current infestation saw both HWA and EHS at elevations up to 530 meters before a sharp decline in infestation. To better understand the potential range expansion of the pests in western Massachusetts, temperature loggers were deployed at 10 representative sites to record over-winter temperatures from December through February. The 2022-23 temperatures were compared to the 2008 temperatures to see the impact of warming. The 10 sites were revisited in March and samples were collected to determine the mortality rate of HWA and EHS. Using a combination of statistical methods and field sampling I am analyzing the range expansion of HWA and EHS.

Jacob Towsley '23 
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