Predicting the Effects of Hemlock Woolly Adelgid on Microhabitat Structure and Small Mammal Communities

Hemlock woolly adelgid (HWA) invasion and preemptive logging practices alter the habitat structure of New England forests and may indirectly affect associated small mammal communities. Microhabitat structure was measured and small mammals were censused in eight large experimental plots to quantify and predict these effects. The Harvard Forest Long-Term Ecological Research experiment is a replicated two-block design that includes four 0.81-ha canopy treatments: 1) Hemlock Control, 2) Hardwood Control, 3) Girdled Treatment, in which hemlock trees were killed by girdling in 2005 and left standing to simulate HWA invasion, and 4) Logged Treatment, in which trees were removed to simulate preemptive logging management practices. Nine microhabitat characteristics were measured from plot photos revealing differences among microhabitat structure. Small mammals were censused with arrays of 49 Sherman traps per plot and population sizes of common species were estimated with mark-recapture analysis. Between 6 and 8 mammal species were recorded in all treatments and species composition varied slightly. Populations of two common rodents ( Peromyscus spp .) were not affected by treatment, but the southern red-backed vole population was greatest in the Girdled treatment. Estimated species richness was greater in the Girdled treatment than the Hemlock control, but richness did not differ between Girdled and Logged treatments, which suggests preemptive logging is as detrimental to some small mammal species as HWA invasion. Overall, nine years post disturbance, there is little evidence of a major shift in small mammal community structure in response to woolly adelgid invasion, with only minor changes in relative abundance.