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Harvard Forest Symposium Abstract 2015

  • Title: Does hemlock decline affect sex and age structure of red backed salamanders’ population in Harvard forests?
  • Primary Author: Ahmed Siddig (University of Khartoum)
  • Additional Authors: Simone Johnson (Lincoln University (Missouri)); Alison Ochs (Mount Holyoke College); Claudia Villar-Leeman (Bowdoin College)
  • Abstract:

    Background: Amphibians including salamanders are abundant, ecologically important and sensitive to local habitat disturbances. As eastern hemlocks (Tsuga canadensis) stands are declining in New England region due to the infestations by the introduced hemlock wooly adelgid (HWA) (Adelges tsugae), several ecological processes and wide range of taxa including amphibians are expected to be affected. For example recent studies have already showed significant reduction in salamander’s abundance in hemlock dominated forests at central Massachusetts. However this reduction in abundance is not known whether it accompanied by changes in demographic characteristics such as sex and life stage structure or not.

    Objectives: this study aims to assess the impacts of decline in eastern hemlock stands on sex and life stage structure of eastern red back salamander (Plethodon cinereus) population in Harvard forest.

    Methodology: Study has been conducted in the Hemlock Removal Experiment (HeRE) in Harvard Forest, Petersham MA. The experiment is a replicated block design including two blocks within each three treatments that simulate the three possible scenarios associated with hemlock decline due to HWA. Each block has four plots treated with girdling (i.e. slow death by HWA), logging (i.e. preemptive response), and hardwood control (i.e. anticipated future) beside untreated hemlock stands (i.e. healthy conditions) as control. In each plot we established two 60m transects in each of which we distributed five 1×0.25-coverboards spaced 15 meters from each other. Underneath each cover board Salamanders were counted, sexed, and aged based on snout-vent length (SVL) 2013 & 2014 at Harvard Forest, Data analyzed using Chi-sq. test to assess the hypothesis that HeRE treatments has no effects on sex structure as well as life stage structure.

    Results: total number of salamanders captured in spring is significantly higher than the captures of summer as well as fall. While sex ratio (male: female) found to be 1:1 in spring and 3:1 in summer, the life stages (adults: subadults: juveniles) are significantly skewed towards subadults in both seasons. Population structure is relatively stable although the treatments have significantly affected abundance we were not able to detect any impacts on sex structure (Chi -squared = 1.8303, df = 3, p-value = 0.6084) and life stage structure (Chi -squared = 7.4286, df = 6, p-value = 0.283).

    Conclusions: Given the significant number of captures in spring we suggest that P. cinereus monitoring programs in Harvard forest should be between May and mid-June. Hemlock treatments do affect abundance but not the demographic structure. More research is needed with larger sample size and may be better methods & design.

  • Research Category: Biodiversity Studies; Conservation and Management; Physiological Ecology, Population Dynamics, and Species Interactions