Coniferous conservation supporting a plethora of plethodontids: Implications of conserving eastern hemlock (Tsuga canadensis) on southern Appalachian montane salamanders

Abstract

Hemlock woolly adelgid (Adelges tsugae; HWA), an invasive aphid-like insect, was first documented on the East Coast of the United States in the 1950 s. Hemlock woolly adelgid is an herbivore which primarily feeds at the needle base of hemlock tree species (Pinaceae: Tsuga). With no evolutionary defenses and few biotic controls, the eastern and Carolina hemlock (Tsuga canadensis and Tsuga carolinensis) serve as the primary diet of HWA in eastern North America. The invasive pest began to spread rapidly throughout the hemlock’s range causing defoliation and death of the trees within 4 – 10 years. With the loss of the foundational species, Tsuga canadensis, several microenvironmental changes were documented. Microenvironmental changes in response to biological invasions and anthropogenic forestry practices can lead to shifts in populations of physiologically sensitive taxa such as salamanders and their prey, terrestrial arthropods.National Park Service (NPS) staff at Great Smoky Mountains National Park manage HWA by treating eastern hemlocks with the neonicotinoid pesticides, imidacloprid and dinotefuran. To measure indirect effects of eastern hemlock mortality, and HWA management, this study collected data on several parameters in hemlock-dominated stands that have been repeatedly managed by the NPS and stands which were un-managed and where HWA has reduced the hemlock canopy. Our major objectives were to assess microenvironmental, vegetative, and arthropod community differences between managed and un-managed eastern hemlock stands and analyze those differences with respect to woodland salamander abundance. Answering these questions should provide insight into indirect impacts of the invasive species, HWA, on indicator species, terrestrial salamanders, through changes in prey availability and microenvironmental parameters. A mixed effects linear model using elevation range as a random effect or block was used to model salamander abundance with prey availability, microenvironmental parameters, and HWA management as a factor. Our results indicate that HWA management was the strongest predictor of total salamander abundance and for Plethodon jordani and Desmognathus wrighti abundance individually. We found over five times the relative salamander abundance in sites which had been managed for HWA compared to sites which had been left un-managed.Funding: This work was supported by the University of Tennessee, Knoxville Department of Earth and Planetary Sciences, Knoxville, TN.