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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Environmental Conservation

Year Degree Awarded

2015

Month Degree Awarded

May

First Advisor

Aaron M. Ellison

Second Advisor

Curt R. Griffin

Third Advisor

Scott Jackson

Fourth Advisor

Bethany Bradley

Subject Categories

Biodiversity | Population Biology | Terrestrial and Aquatic Ecology

Abstract

The objective of this study is to assess the potential of two amphibians species, Eastern Red-backed Salamander (Plethodon cinereus (Green)) and Eastern Red-spotted Newt (Notopthalmus viridescens viridescens Rafinesque), as indicator species of forest disturbances at Harvard Forest, located in Petersham, Massachusetts, United States. Specifically, I 1) assess the impacts of these focal species to decline of hemlock forests in Harvard Forest; 2) calibrate abundance indices of P. cinereus based on artificial and natural objects surveys with a population size estimator based on depletion sampling; and 3) assess the potential of these salamanders as indicator species by developing an objective and multimetric method.

My results showed that decline of Eastern Hemlock (Tsuga canadensis) forests due to invasive insects has increased the occupancy of P. cinereus but significantly reduced its estimated abundance and detection probability. Similarly, the estimated abundance of N. v. viridescens also declined dramatically after hemlock decline. The anticipated transition from forests dominated by T. canadensis to mixed-hardwood may alter the abundance and detection probability of both salamander species by up to 50%. Abundance indices based on both cover board and natural object surveys were able to be calibrated using density estimates of P. cinereus derived from depletion (removal) surveys. The cover-board abundance index was eight times higher than the estimated density of P. cinereus, whereas the natural object survey was half the size of the density estimator. I introduced the Indicator Species Potential (ISP) index – a multi-metric method to quantify the efficacy of indicator species in classifying sites, monitoring ecological changes, and assessing desired management conditions. When applied to salamanders as potential indicators of changes in forests in Massachusetts, the ISP suggests that P. cinereus is a reasonable indicator for ecological change in hemlock stands whereas N. viridescens is a potential IS in mixed hardwoods. Overall, the ISP shows promise as a method for summarizing ecological and statistical information about potential IS in a single value.

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