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

Alison Ochs,Ahmed Siddig

doi:10.3390/environments4010008

Abstract

Hemlock forests of the northeastern United States are declining due to the invasive hemlock woolly adelgid (HWA) (Adelges tsugae). Hardwood species replace these forests, which affects soil properties that may influence other communities, such as red-backed salamanders (red-backs) (Plethodon cinereus). This study examined the effects of HWA invasion on soil properties and how this affects red-backs at the Hemlock Removal Experiment at Harvard Forest, which consists of eight 0.8 ha plots treated with girdling to simulate HWA invasion, logging to simulate common management practices, or hemlock- or hardwood-dominated controls. Coverboard surveys were used to determine the relative abundance of red-backs between plots during June and July 2014 and soil cores were collected from which the bulk density, moisture, pH, temperature, leaf litter, and carbon-nitrogen ratio were measured. Ordination provided a soil quality index based on temperature, pH, and carbon-to-nitrogen ratio, which was significantly different between plot treatments (p < 0.05) and showed a significant negative correlation with the red-back relative abundance (p < 0.05). The findings support the hypothesis that red-backs are affected by soil quality, which is affected by plot treatment and thus HWA invasion. Further studies should explore how salamanders react in the long term towards changing environments and consider the use of red-backs as indicator species.

Highlights

The hemlock forests of the northeastern United States are currently declining due to an invasive insect, the hemlock woolly adelgid, Adelges tsugae Annand, which attaches to the base of eastern hemlock (Tsuga canadensis) needles and causes a slow death of the tree over several years [1,2].With the decline of the hemlock, the characteristic heavy canopy and cool, dark microclimate give way to hardwood species such as oak, birch, and maple [2,3,4,5]
Our data show a distinct difference in principle component 2 (PC2) between plot treatments, and a noticeable correlation between PC2 and salamander relative abundance
As the plots reflected forest changes due to hemlock woolly adelgid (HWA) invasion, our data support that invasion by HWA affects the forest and causes changes in some soil characteristics, which affects red-backs

Summary

Introduction

With the decline of the hemlock, the characteristic heavy canopy and cool, dark microclimate give way to hardwood species such as oak, birch, and maple [2,3,4,5]. This transition from hemlock to hardwood forest is expected to bring changes to the microclimate, including changes in the soil properties [4,6]. Many aspects of the soil are affected by vegetation. Variables such as pH can be affected by changes in leaf litter inputs and cation uptake [7]. Soil moisture can be affected by canopy cover and has been shown to decrease in areas

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