PS 26-43
Effects of hemlock woolly adelgid on small mammal richness and community assemblages in eastern hemlock forests

Tuesday, August 11, 2015
Exhibit Hall, Baltimore Convention Center
Allyson Degrassi, Department of Biology, University of Vermont, Burlington, VT
Aaron Ellison, Harvard Forest, Harvard University, Petersham, MA
Nicholas J. Gotelli, Biology, University of Vermont, Burlington, VT

Eastern hemlock is declining in abundance from the effects of the invasive sap-sucking insect hemlock woolly adelgid. The loss of hemlock forests may impact community composition of associated small mammals. I censused small mammal communities in experimental plots at Harvard Forest to quantify these effects.

The Harvard Forest Long-Term Ecological Research experiment is a replicated two-block design that includes four-0.81ha canopy treatments:1) hemlock control, in which hemlocks trees are dominant, 2) hardwood control, in which young hemlocks are present, but mid-successional hardwoods are dominant, 3) girdled treatment, in which hemlock trees have been girdled and killed to simulate the effect of woolly adelgid invasion, and 4) logged treatment, in which hemlocks and commercial hardwood species have been removed to simulate the effect of pre-emptive forest management. Small mammal trapping grids spanning 0.49ha and consisting of 49 Sherman live-traps were placed within each canopy treatment. Traps baited with sunflower seed and raw cotton were set during the months of June and July 2012-2014. Multi-season occupancy modelling with spatial replication was used to examine changes in the abundance, species composition, and species richness of small mammals among the four canopy treatments.


A total of 11,403 trapping nights resulted in approximately 1,933 captures. The number of captures varied among years from a low of approximately 138 captures (2013) to a high of approximately 977 captures (2014). Species richness among all treatments did not vary (10 species per treatment). Rodents and shrews were captured at varying abundances among the four treatments. In hemlock and hardwood treatments, deer mice, white-footed mice, and southern-flying squirrels were captured more frequently than southern red-backed voles. However, in girdled and logged treatments, southern red-backed voles and eastern chipmunks were captured more frequently than mice and southern-flying squirrels.

These preliminary data suggest that hemlock woolly adelgid infestation may affect the abundance and composition of small mammal communities, but does not affect species richness. Because eastern hemlocks are not expected to recover from the adelgid invasion, there may be widespread changes in the abundance and composition of small mammal assemblages.