Do Terrestrial Salamanders Indicate Ecosystem Changes in New England Forests?

Abstract

Long-term ecological research (LTER) and monitoring programs accrue invaluable ecological data that inform policy and improve decisions that enable adaptation to and mitigation of environmental changes. There is great interest in identifying ecological indicators that can be monitored easily and effectively to yield reliable data about environmental changes in forested ecosystems. However, the selection, use, and validity of ecological indicators to monitor in LTER programs remain challenging tasks for ecologists and conservation biologists. Across the eastern United States of America, the foundation tree species eastern hemlock (Tsuga canadensis (L.) Carrière) is declining and dying from irruptions of a non-native insect, the hemlock woolly adelgid (Adelges tsugae Annand). We use data from the Harvard Forest LTER site’s Hemlock Removal Experiment together with information from other eastern US LTER sites to show that plethodontid salamanders can be reliable indicators of ongoing ecological changes in forested ecosystems in the eastern USA. These salamanders are abundant, they have a history of demographic stability, are both predators and prey, and can be sampled and monitored simply and cost-effectively. At the Harvard Forest LTER, red-backed salamanders (Plethodon cinereus Green) were strong indicators of intact forests dominated by eastern hemlock (Tsuga canadensis); their high site fidelity and habitat specificity yielded an indicator value (robust Dufrêne and Legendre’s “IndVal”) for this species of 0.99. Eastern red-spotted newts (Notopthalmus viridescens viridescens Rafinesque) were better indicators of nearby stands made up of young, mixed hardwood species, such as those which replace hemlock stands following adelgid infestation. At the Hubbard Brook and Coweeta LTER sites, plethodontid salamanders were associated with intact riparian habitats, which may also be dominated by eastern hemlock. We conclude that plethodontid salamanders satisfy most criteria for reliable ecological indicators of environmental changes in eastern US forests.

Eastern red-backed salamanders: A comprehensive review of an undervalued model in evolution, ecology, & behavior

“…The pair of Burton & Likens' (1975a, 1975b studies have since been cited by hundreds of subsequent studies, some of which argue for the use of P. cinereus as an ecosystem indicator species (e.g. Welsh & Droege, 2001;Siddig, Ochs, & Ellison, 2019), or for the overall importance of plethodontids to terrestrial forest ecosystems (e.g., Davic & Welsh, 2004), and indeed have shaped the thinking of many researchers working on North American plethodontid salamanders since (but see Riedel et al, 2008 andOuellet, 2015 for caution about the use of P. cinereus as an indicator species). Thus, we found it odd that ecosystem ecology was neglected by Petranka (1998), although this seems to be the case for all species accounts throughout the book.…”

“…In New York, Beier et al (2012) found a positive relationship between P. cinereus abundance and a well-defined calcium gradient, while in Massachusetts, Ochs & Siddig (2017) found P. cinereus was more prevalent in forests with lower soil pH, lower carbon to nitrogen (C:N) ratios, and lower temperatures. The authors note that the first two characteristics, low soil pH and low C:N ratios, are characteristic of hemlock stands, which used to be much more common within the range of P. cinereus prior to the arrival of hemlock wooly adelgid (Siddig et al, 2019). The loss of hemlocks and other massive ecosystem changes as a result of invasive species who affect fundamental environmental properties relied on by forest floor inhabitants (e.g.…”

“…In the last two decades, it has been suggested that P. cinereus be considered as an indicator species for a variety of ecosystem properties (e.g., Welsh & Ollivier, 1998;Welsh & Droege, 2001). Siddig et al (2019) agreed that P. cinereus may be an indicator species used to monitor changes in eastern hemlock forest ecosystems due to their sensitivity to key stressors and changing environmental conditions. Along with several studies hypothesizing and testing the connection between a changing climate and color phenotype ratios in a population (see Systematics and Geographic Variation, above), Moore & Ouellet (2015) concluded that climate variables do not influence color phenotype ratios broadly across the range of P. cinereus.…”