Salamander Abundance at Harvard Forest 2003-2004

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.

1. 东红背蝾螈相对丰度
东部铁杉（Tsuga canadensis）作为重要的晚演替树种，当前在该区域正受到铁杉球蚜（Adelges tsugae）的威胁——这是一种源自日本、类似蚜虫的小型入侵性昆虫。尽管已有诸多研究证实鸟类与哺乳类物种与东部铁杉纯林存在关联，但针对该林型下两栖动物相对丰度的调研却极为匮乏。东红背蝾螈（Plethodon cinereus）是森林生态系统的重要组成部分：在哈伯德布鲁克实验林（Hubbard Brook Experimental Forest）中，其种群丰度极高，生物量可达繁殖鸟类的两倍，与小型哺乳类相当。此外，红背蝾螈处于食物网的中间层级，既是土壤无脊椎动物的重要捕食者（可潜在影响土壤呼吸速率），同时也是鸟类、爬行类与小型哺乳类等大型脊椎动物的猎物。基于上述特征，加之相较于其他森林动物类群，其种群丰度的年际波动极低，东红背蝾螈被视作评估森林健康状况的优质指示物种。本研究的目标如下：① 采用人工覆盖物（artificial cover objects, ACOs），在马萨诸塞州皮茨汉姆的哈佛森林（Harvard Forest）中，建立东部铁杉纯林与混交落叶林内东红背蝾螈相对丰度的基准数据；② 检验不同林型下红背蝾螈相对丰度是否存在差异；③ 分析红背蝾螈相对丰度与土壤pH值及地表温度的相关性。

2. 幼年东部红斑蝾螈最小种群密度
本研究通过对哈佛森林（Harvard Forest）内Prospect Hill、Slab City、Simes及Tom Swamp片区的10个林分（5个东部铁杉纯林、5个混交落叶林）开展样带目视调查，估算了幼年东部红斑蝾螈（Notophthalmus viridescens viridescens，俗称“红鳗螈”）的最小种群密度，为该类群提供基准数据。本研究的目标包括：① 获取哈佛森林内红鳗螈最小种群密度的基准数据；② 检验不同林型下红鳗螈最小种群密度是否存在差异；③ 分析红鳗螈最小种群密度与土壤pH值及地表温度的相关性；④ 检验最小种群密度估算值是否存在季节差异。

3. 限时密集搜索法
2003年秋季与2004年春季，研究团队在哈佛森林上述片区的10个林分（5个东部铁杉纯林、5个混交落叶林）内开展了1平方米区域的2分钟密集搜索，以调查东红背蝾螈（Plethodon cinereus）与幼年东部红斑蝾螈（俗称“红鳗螈”）的种群丰度。本研究旨在补充现有调研成果：前者采用人工覆盖物（ACOs）调查东红背蝾螈相对丰度，后者则通过样带行走法估算红鳗螈的最小种群密度。

4. 人工覆盖物试验
无肺螈科（Plethodontidae）蝾螈作为森林动物群落总生物量的重要组成部分，正日益被视作森林健康状况的重要指示物种。此外，该类群处于食物网中间层级，既是土壤无脊椎动物的重要捕食者（可潜在影响土壤呼吸速率），同时也是鸟类、小型哺乳类与爬行类等高等脊椎动物的猎物。由于活动范围狭小且为陆地繁殖，无肺螈属（Plethodon）物种的丰度年际变异系数也低于其他动物类群。安装并监测人工覆盖物（artificial cover objects, ACOs）是一种相对新兴的无肺螈丰度评估技术。不同规格的木质人工覆盖物已被成功用作陆生蝾螈的监测工具，但现有研究担忧，木质覆盖物会随风化作用逐渐改变其下方生境的质量，进而无法准确反映蝾螈种群丰度的真实变化。而沥青瓦等抗腐性更强的材料，或许能在更长时间内维持生境的一致性。本研究针对同一表面积（1米×0.25米）但材质不同的人工覆盖物展开对比试验：一组为2厘米厚的粗切东部铁杉木板，另一组为沥青瓦，以比较该区域最常见的无肺螈物种——东红背蝾螈（Plethodon cinereus）在两类覆盖物下的观测率。