Salamander Abundance at Harvard Forest

• Investigators: Elizabeth Colburn, David Foster, Brooks Mathewson
• Contact: Brooks Mathewson
• Start date: 2003-08-14
• End date: 2004-10-29
• Location: Harvard Forest
• Latitude: +42.45 to +42.54
• Longitude: -72.22 to -72.17
• Elevation: 230 to 340 meters
• Taxa: Adelges tsugae (hemlock woolly adelgid), Ambystoma maculatum (spotted salamander), Notophthalmus viridescens (eastern red-spotted newt), Plethodon cinereus (eastern redback salamander), Tsuga canadensis (eastern hemlock)
• Keywords: artificial cover object, eastern redback salamander, hemlock, hemlock wooly adelgid, red eft, spotted salamander
• Abstract:

  1. Eastern redback salamander relative abundance

  Eastern hemlock (Tsuga canadensis), an important late successional tree species, is currently threatened in this region by the hemlock woolly adelgid (Adelges tsugae), a small aphid-like invasive insect from Japan. While many species of birds and mammals have found to be associated with eastern hemlock dominated stands, there have been very few studies examining amphibian relative abundance in this forest type. Eastern redback salamanders (Plethodon cinereus) are important components of the forest ecosystem as they are extremely abundant with a biomass found to be twice that of breeding birds and equal to small mammals in the Hubbard Brook Experimental Forest. In addition, redbacks are positioned in the middle of the food web where they are important predators of soil invertebrates, potentially impacting soil respiration rates, and prey for larger vertebrates such as birds, reptiles, and small mammals. Redbacks have been cited as excellent indicators of forest health due to these characteristics as well as their low annual variation in abundance compared to other forest fauna. The objectives of this study was to 1) establish baseline data on eastern redback salamander relative abundance in eastern hemlock dominated stands and mixed deciduous stands in the Harvard Forest in Petersham, MA using artificial cover objects (ACOs) 2) test for differences in redback relative abundance based on forest type, 3) test for correlations between redback relative abundance and soil pH and forest floor temperature.

  2. Juvenile eastern red-spotted newt minimum density

  This study provides baseline estimates of juvenile eastern red-spotted newt (Notophthalmus viridescens viridescens) or "red eft" minimum density through visual surveys of transects in ten forest stands, five eastern hemlock (Tsuga canadensis) dominated and five mixed deciduous, located in the Prospect Hill, Slab City, Simes, and Tom Swamp tracts of Harvard Forest. The objectives of this study were to 1) acquire baseline minimum red eft density data at Harvard Forest, 2) test for potential differences in minimum density based on forest type, 3) test for correlations between minimum density and soil pH and forest floor temperature, 4) test for seasonal differences in minimum density estimates.

  3. Time-constrained intensive searches

  Intensive two minute searches of 1-m2 were conducted to measure eastern redback salamander (Plethodon cinereus) abundance and juvenile eastern red-spotted newt (Notophthalmus viridescens viridescens) or "red eft" abundance at ten stands, five eastern hemlock (Tsuga canadensis) dominated and five mixed deciduous stands, in the Prospect Hill, Slab City, Simes, and Tom Swamp tracts of Harvard Forest in fall 2003 and spring 2004. The objective of this study was to supplement other studies using artificial cover objects (ACOs) to measure eastern redback salamander relative abundance and transect walks to measure minimum density of red efts at Harvard Forest.

  4. Artificial cover objects

  Plethodontid salamanders are increasingly being cited as important indicators of forest health as they are major contributors to the overall faunal biomass in a forest. In addition, they are positioned in the middle of the food web where they are important predators of soil invertebrates, potentially impacting soil respiration rates, as well as prey for higher vertebrates such as birds, small mammals, and reptiles. Plethodon species also have lower annual coefficients of variation than other animals due to their small home ranges and terrestrial breeding habits. A relatively new technique used in assessing plethodontid abundance is the installation and monitoring of artificial cover objects (ACOs). Wood ACOs of different sizes have been effectively used as terrestrial salamander monitoring tools. However, there is a concern that the quality of habitat under wooden cover objects may change over time as they weather thus altering their ability to track real changes in salamander abundance. More rot-resistant materials such as asphalt shingles may provide more consistent habitat over time. This study compared the observation rates of the most common plethodontid species in this region, the eastern redback salamander (Plethodon cinereus) under artificial cover objects (ACOs) of the same surface area - 1m x 0.25m - but different materials - 2cm thick rough-cut eastern hemlock boards and asphalt shingles.

• Methods:

  1. Eastern redback salamander relative abundance

  ACO stations were set up at 50m intervals along transects in the Prospect Hill, Slab City, Simes, and Tom Swamp tracts of Harvard Forest. Each ACO station consisted of one 2cm thick rough-cut eastern hemlock board (1m x 0.25m) and one asphalt shingle (1m x 0.25m) located 3m apart and parallel to the transect. Each of the ten stands in this study contained between four and twelve ACO stations. ACOs were monitored between one and six times per season. Temperature measurements were obtained through the installation of one remote temperature sensor (iButton) placed in the center of each transect and set to record temperature every half hour in spring 2004 (4/22/04 - 6/7/04) and every hour in fall 2004 (9/22/04 - 11/12/04). In early winter 2003 five soil samples were taken from random points just below the leaf litter in each transect and left to dry for two weeks and then soil pH was measured in the lab.

  2. Juvenile eastern red-spotted newt minimum density

  Minimum red eft density estimates were obtained by counting the number of red efts encountered within 0.5m of both sides of a transect. Between two and six transects were established in each stand. Transect lengths were between 73m and 107m, with the majority (20 of 31 transects) 90m long. Only red efts entirely within the surveyed area were counted. All searches were conducted by the same observer. The number of surveys per season in each stand varied from one to eight. The highest density value obtained for a stand in a season was used as the minimum density of red efts in that stand. This value was used as opposed to the average, because it is assumed that values lower than the maximum were a result of conditions that were not optimal for red efts to be on the surface of the forest floor. Both seasonal averages and maximums are reported in the data set. Temperature measurements were obtained through the installation of one remote temperature sensor (iButton) placed in the center of each transect and set to record temperature every half hour in spring 2004 (4/22/04 - 6/7/04) and every hour in fall 2004 (9/22/04 - 11/12/04). In early winter 2003 five soil samples were taken from random points just below the leaf litter in each transect and left to dry for two weeks and then soil pH was measured in the lab.

  3. Time-constrained intensive searches

  Twenty 1-m2 quadrats were searched in each of the ten stands both fall 2003 and spring 2004. Quadrats were selected randomly along transects established in each stand for a companion study examining red eft density using transect walks. Searches were conducted in the last week of September 2003 and the first week of October 2003. In the spring, intensive searches were conducted on eight separate dates between mid-April 2004 and mid-June 2004. On all sampling days an equal number of quadrats were searched in eastern hemlock and mixed deciduous stands, except at one site in the fall in which different forest types were searched on successive days. I searched for redbacks and red efts on the surface of the forest floor, within the leaf litter, and under natural cover objects such as stones and decaying logs. After each search cover objects were restored to as close to their original position as possible.

  4. Artificial cover objects

  ACO stations were set up at 50m intervals along transects established for a separate study of red eft minimum density in the Prospect Hill, Slab City, Simes, and Tom Swamp tracts of Harvard Forest. Each ACO station consisted of one 2cm thick rough-cut eastern hemlock board (1m x 0.25m) and one asphalt shingle (1m x 0.25m) located 3m apart and parallel to the transect. Each of the ten stands in this study contained between four and twelve ACO stations. ACOs were monitored between one and six times per season. Temperature measurements were obtained through the installation of one remote temperature sensor (iButton) placed in the center of each transect and set to record temperature every half hour in spring 2004 (4/22/04 - 6/7/04) and every hour in fall 2004 (9/22/04 - 11/12/04). In early winter 2003 five soil samples were taken from random points just below the leaf litter in each transect and left to dry for two week and then soil pH was measured in the lab.

• Related datasets: HF038