The effects of the invasive sap-sucking insect, hemlock woolly adelgid, are causing a decline in eastern hemlock forest abundance. The loss of these foundation species, due to hemlock woolly adelgid and forest management practices such as logging, may impact small mammal distribution. I censused small mammal communities in experimental plots at Harvard Forest to quantify the impacts of forest disturbance caused by hemlock woolly adelgid and preemptive logging practices.
The Harvard Forest Long-Term Ecological Research experiment (LTER) 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 preemptive 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. Occupancy modelling was used to examine changes in site occupancy and probability of detection 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 138 captures (2013) to a high of 977 captures (2014). Species richness among all treatments did not vary (10 species), but shifts in community assembly did occur. Rodents and shrews were captured at varying abundances among the four treatments. Deer mice and southern-flying squirrels were captured more frequently in hemlock and hardwood controls than southern red-backed voles. However, southern red-backed voles were captured more frequently in girdled and logged treatments than mice and southern-flying squirrels.
These data suggest that disturbance caused by girdling and logging impacts site occupancy, estimated abundance, and composition of small mammal communities, but does not affect species richness. The effects on small mammal distribution did not differ significantly between the girdled and logged treatments, which suggests that preemptive logging is as detrimental to small mammal distribution as tree girdling caused by hemlock woolly adelgid. 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.