Mark-Recapture of Rodent and Shrew Populations in a Declining Hemlock Stand at Harvard Forest 2012

Eastern Hemlocks (Tsuga canadensis) are foundation species, which are known to have a large influence on the species composition and ecosystem dynamics. The purpose of this study was to understand how rodent species richness and composition differed among different hemlock treatments consisting of intact forest, logged forest, and invaded hemlock stands in the Harvard Forest of Petersham, MA. Sherman live traps were arranged on 7x7m grids covering 0.49ha in four different hemlock treatments that were established in 2003: 1) the logged treatment, where commercial trees were removed 2) the girdled treatment, where the hemlocks were girdled using a chainsaw, thus killing the trees, and mimicking the effects of the woolly adelgid, an invasive insect 3) the hemlock control which is where hardwoods are at least 70% hemlocks, and 4) the hardwood control, where other hardwood species are dominate. Animals were marked and recaptured from June-July. Using Schnabel methods for population estimate, there appeared to be a shift in the population from more abundant Gapper’s Red-backed vole, Clethrionomys gapperi in the logged and girdled treatments to white-footed and deer mice (Peromyscus spp) in the hemlock and hardwood control plots. This shift in population may indicate that hemlocks support Peromyscus spp over voles. The species richness and overall population dynamic of these rodents surveyed may lead to a greater understanding as to the potential affect they may have on the seed dispersal in these plots and could account for many interactions between the vegetation and the animals also present.

加拿大铁杉（Tsuga canadensis）是一类基础建群种，其对群落物种组成与生态系统动态具有显著调控作用。本研究旨在探究美国马萨诸塞州皮茨汉姆市哈佛大学森林保护区内，不同铁杉处理样地间啮齿动物的物种丰富度与群落组成差异。实验于2003年设置4组铁杉处理样地，在覆盖总面积达0.49公顷的7×7米样方网格中布设谢尔曼活捕笼（Sherman live traps），具体处理如下：1. 采伐处理样地：移除商品用材树种；2. 环割处理样地：使用链锯对铁杉进行环割以杀死植株，模拟入侵昆虫铁杉球蚜（woolly adelgid）的危害效应；3. 铁杉对照样地：样地内铁杉占比不低于70%；4. 硬阔对照样地：以其他阔叶树种为优势种。研究于6-7月间对捕获的啮齿动物进行标记并重捕。采用施纳贝尔种群估计法（Schnabel methods）进行种群分析的结果显示，种群结构发生显著转变：采伐与环割处理样地中占优势的加普红背䶄（Clethrionomys gapperi），在铁杉对照与硬阔对照样地中被白足鼠及鹿鼠（Peromyscus spp.）替代。这种种群结构转变表明，铁杉生境更有利于鹿鼠属（Peromyscus spp.）种群存续，而非红背䶄。本次调查揭示的啮齿动物物种丰富度与整体种群动态，有助于深入理解此类啮齿动物对样地内种子传播的潜在影响，并可为阐释样地内植被与伴生动物间的多种互作关系提供科学依据。