Mid-Holocene Hemlock Decline in Eastern North America Linked with Phytophagous Insect Activity

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Abstract
Macrofossil evidence indicates that the mid-Holocene hemlock [Tsuga canadensis L. (Carr.)] decline that occurred over a wide area in eastern North America was associated with phytophagous insect activity. In situ hemlock macrofossils and insect remains found in a paludified dunefield at the northern limit of hemlock testify that two defoliation events occurred at 4910 ± 90 and 4200 ± 100 yr B.P., respectively. The sharp coincidence of remains from hemlock needles with chewing damage typical of hemlock looper feeding, head capsules from the hemlock looper (Lambdina fiscellaria) and the spruce budworm (Choristoneura fumiferana), absence of hemlock fruiting remains, and tree-ring anomalies in fossil hemlocks that died prematurely (<165 yr) suggest that defoliation affected hemlock reproductive capacity and pollen productivity, or more likely caused mass mortality. Our findings indicate that defoliation can affect ecosystems for centuries, especially when long-lived tree species are involved.

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