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Evaluating the role of insects in the middle-Holocene Tsuga decline1

Oswald, W. Wyatt, Doughty, Elaine D., Foster, David R., Shuman, Bryan N., Wagner, David L.
The journal of the Torrey Botanical Society 2017 v.144 no.1 pp. 35-39
Chironomidae, Coleoptera, Lambdina fiscellaria fiscellaria, Tsuga canadensis, basins, climate, drought, forests, insect pests, sediments, Massachusetts
The middle-Holocene decline of Tsuga canadensis (L.) Carrière (eastern hemlock) across eastern North America has been attributed to various causes, including the widespread outbreak of an insect pest, such as Lambdina fiscellaria (hemlock looper). We tested this hypothesis by searching for insect remains in sediment cores from Hemlock Hollow, a small basin in north-central Massachusetts. Previous analyses of this site demonstrated that it has been surrounded by Tsuga forest for the past 10,000 yr. We found the remains of chironomids and beetles in the cores but not in sediments dating to the interval of low Tsuga abundance; remains of Lambdina fiscellaria were not encountered. These results are consistent with the interpretation that the decline of Tsuga at Hemlock Hollow was not caused solely by an insect outbreak. The presence of Lambdina fiscellaria remains in middle-Holocene sediments at other sites in the region may reflect local outbreaks, perhaps facilitated by drought or other changes in climate that stressed Tsuga populations.