PS 25-89
Effects of hemlock logging on ant biodiversity patterns in northern hemlock-hardwood forests
Eastern hemlock, Tsuga canadensis, is a foundation tree species that creates unique aesthetics and microclimates due to shading and longevity. Hemlock Woolly Adelgid (HWA; Adelges tsugae) is infesting and killing hemlock trees throughout their eastern range but has only recently been found in parts of Maine. Biodiversity patterns and ecosystem processes of hemlock forests are not well characterized in Maine and the goal of this study is to characterize the structure and function of these forests prior to HWA infestation and in response to salvage logging for eastern hemlock. Specifically, we investigated the relationships between ant community composition and microclimate variables. The influential role of ants as ecosystem engineers, their rapid response to environmental changes, and their large biomass makes ant biodiversity a good indicator of ecosystem integrity. Through pitfall trapping we examined ant species diversity in 25 logged and 25 unlogged 100 m2 plots from three uninfested hemlock stands. To determine how ant abundance was influenced by environmental variables we also collected data about leaf litter depth, photosynthetically active radiation (PAR, μmol/m2) as measured by Li-Cor sensors, % soil moisture determined by time domain reflectometry, and air temperature recorded with mini dataloggers.
Results/Conclusions
We found that that there were significantly higher light levels (p < 0.001) and thicker leaf litter (p < 0.0001) in the logged plots. Plots had been logged 1-2 years prior to the beginning of the experiment. On average, 32% soil moisture was recorded in the middle of the growing season in both logged and unlogged plots. Annual average temperature did not differ significantly between treatments in 2011, but was significantly higher in logged plots for 2012 (p = 0.026). Ant species composition appeared to respond to logging-induced changes in environmental variables. The dominant ant genera in both logged and unlogged plots included Aphaenogaster, Camponotus, Formica, Myrmica, and Lasius. However in logged plots two additional genera were recorded, Tapinoma and Temnothorax. In the logged plots the proportion of Aphaenogaster, Myrmica, and Lasius decreased over time while Camponotus and Formica increased over time. In unlogged plots the proportion of Aphaenogaster, Camponotus, and Formica increased over time while Myrmica and Lasius decreased. These changes in ant species abundance may lead to changes in ecosystem functions due to the different functional roles of each ant genera.