Assessing the impacts of the decline of Tsuga canadensis stands on two amphibian species in a New England forest

Abstract

Citation: Siddig, A. A. H., A. M. Ellison, and B. G. Mathewson. 2016. Assessing the impacts of the decline of Tsuga canadensis stands on two amphibian species in a New England forest. Ecosphere 7(11):e01574. 10.1002/ecs2.1574Abstract. Disturbances such as outbreaks of herbivorous insects and pathogens can devastate unique habitats and directly reduce biodiversity. The foundation tree species Tsuga canadensis (eastern hemlock) is declining due to infestation by the nonnative insect Adelges tsugae (hemlock woolly adelgid). The decline and expected elimination of hemlock from northeastern U.S. forests is changing forest structure, function, and assemblages of associated species. We assessed 10 years of changes in occupancy, detection probability, and relative abundance of two species of terrestrial salamanders, Plethodon cinereus (eastern redback salamander) and Notopthalmus viridescens viridescens (eastern red-spotted newt), to the experimental removal in 2005 of T. canadensis at Harvard Forest. Salamanders were sampled under cover boards and using visual encounter surveys before (2004) and after (2005, 2013, 2014) canopy manipulations in replicate 0.81-ha plots. In 2004, occupancy of P. cinereus was 35% lower in stands dominated by T. canadensis than that in associated mixed-hardwood control stands, whereas detection probability and estimated abundance of P. cinereus were, respectively, 60% and 100% greater in T. canadensis stands. Estimated abundance of N. v. viridescens in 2004 was 50% higher in T. canadensis stands. Removal of the T. canadensis canopy increased occupancy of P. cinereus but significantly reduced its estimated detection probability and abundance. Estimated abundance of N. v. viridescens also declined dramatically after canopy manipulations. Our results suggest that ten years after T. canadensis loss due to either the adelgid or pre-emptive salvage logging, and 50-70 years later when these forests have become mid-successional mixed deciduous stands, the abundance of these salamanders likely will be <50% of their abundance in current, intact T. canadensis stands. This study adds to our understanding of how forest disturbance, directly and indirectly caused by invasive species, can contribute to declines in the relative abundance of amphibians.

Response of Red-Backed Salamanders (Plethodon Cinereus) to Changes in Hemlock Forest Soil Driven by Invasive Hemlock Woolly Adelgid (Adelges Tsugae)

“…These conclusions are timely and consistent with many recent studies in the region [36][37][38] that found a declining trend in abundance of red-backs in New England forests. Moreover, although the coverage of this study is relatively small, it confirmed our expectations regarding the contribution of invasive pests and habitat disturbances to the wide scale decline of amphibian populations.…”

Decline of a foundation tree species due to invasive insects will trigger net release of soil organic carbon

“…, Siddig et al. ). Based on our comparisons of soil organic layer mass and %C content between hemlock forest and mature birch stands, we estimate a 6.8× difference in the C pool held in the forest floor (477.4 g C/m 2 vs. 70.6 g C/m 2 ), which suggests the potential for a ~4.5 ton C release per hectare if hemlock organic layers decomposed and transitioned to a new, lower equilibrium comparable to nearby mature birch stands.…”

“…, Siddig et al. ). In addition to their influence on ecological communities and other species, foundation tree species like hemlock affect ecosystem processes such as decomposition, nutrient cycling, and carbon sequestration (Ellison et al.…”

Do Terrestrial Salamanders Indicate Ecosystem Changes in New England Forests?

“…We focus on two species of amphibians common in such New England hemlock forests: red-backed salamanders (Plethodon cinerus; hereafter "red backs") and eastern red-spotted newts (Notopthalmus viridescens viridescens; hereafter "red efts"). Both species are highly abundant in the region, and their abundances have been found to decline with the loss of hemlock forest, demonstrating their potential sensitivity to changes in such systems [11,40,41]. Data are drawn from an ongoing experiment at the Harvard Forest Long-Term Ecological Research Site (HFR); some additional comparisons are made with studies of salamanders in two other forested LTER sites, the Hubbard Brook Experimental Forest (HBR) and the Coweeta Experimental Forest (CWT).…”