Skink trapping: Interactive Effects of Deer, Fire and Nitrogen

In 2000 we began to examine impacts of three anthropogenic effects on successional grasslands in an area with rapid woody encroachment toward white pine forest. We established a factorial experiment that manipulates N (0 or 3 g m-2 yr-1), fire (none or every 2nd year), and deer (fenced or open to deer), with a total of 32 plots, each 20 x 20 m. We hypothesized that the response of this ecosystem to the combined effects of fire, N, and herbivory would depend on the ability of pine and other species to invade and the magnitude of their response to the different disturbance factors: warm-season grasses increase with and encourage fire, resist herbivores, and inhibit woody plant invasion (Davis et al. 1998, Inouye et al. 1994); cool-season plants are favored by N deposition (Tilman 1987) but are fire-intolerant and palatable to herbivores; legumes tolerate fire but decrease with herbivory and N deposition; and finally, woody plants are fire-intolerant and may be more susceptible to herbivory. We are measuring treatment effects on composition and diversity of plants and consumers (insects, small mammals, lizards) as well as plant and soil C and N.2000年，我们开展了一项研究，旨在探究三种人为干扰因素对一片正快速发生木本入侵、正向白松林演替的草本群落的影响。我们设置了一项析因实验，对氮素添加量（0或3 g·m⁻²·yr⁻¹）、火烧处理（无火烧或每两年一次）以及鹿类活动（围栏隔离鹿类或鹿类可自由进入）进行操控，共设置32个样地，每个样地面积为20×20米。我们提出如下假说：该生态系统对火烧、氮素与植食作用的复合干扰的响应，将取决于松树及其他物种的入侵能力，以及它们对不同干扰因子的响应强度：暖季型草本植物可随氮素输入增加而扩张，且能促进火烧发生、抵御植食作用并抑制木本植物入侵（Davis等，1998；Inouye等，1994）；冷季型植物得益于氮沉降（Tilman，1987），但不耐火烧且对植食动物具有适口性；豆科植物可耐受火烧，但会随植食作用和氮沉降而丰度下降；最后，木本植物不耐火烧，且可能更易受到植食动物的取食影响。本研究正在测定各处理对植物与消费者（昆虫、小型哺乳动物、蜥蜴）的群落组成与多样性，以及植物与土壤的碳（C）、氮（N）含量的影响。