Small mammal abundance: Successional Dynamics on a Resampled Chronosequence

The purpose of this observational study is to describe the dynamics of ecosystem succession. The change in the number, type, and amount of plant and grazing animal species is monitored in more than 20 fields. These fields were previously cultivated, but then abandoned from agriculture at various times in the past. The fields were left undisturbed for plants to develop from seeds within the soil or brought into the fields by wind or animals. Permanent transects have been established in these abandoned fields for purposes of sampling in a consistent location from year to year. Permanent plots along these transects have been used to sample soil nutrients, (in particular, nitrogen) abundance of vegetation, species composition and herbivore populations. The sampling occurs approximately every 6 years. In the initial survey, 100 quadrats of size 1 by 0.5 m were sampled per field in 23 different fields. Abandoned fields included in E014 are 4, 5, 10, 21, 24, 26, 27, 28, 32, 35, 39, 40, 41, 44, 45, 47, 53, 70, 72, 76, 77. Fields 22(B), 29(A), and 69(C) were originally included in E014 but used for other purposes shortly after the start of the study. This experiment was established in 1983 and 1989 by principal investigators Johannes Knops and David Tilman.

Past work at CDR and elsewhere has demonstrated an overriding influence of fire frequency in maintaining prairie openings and oak savanna at the prairie-forest border. Fire regimes harm some types of species while favoring others and drive light and nutrient dynamics, which in turn drive community functional attributes and diversity levels. Ultimately, fire frequency interacts with climate, N deposition, land use, and biotic invasion to determine the outcomes of tree-grass interactions and the dynamics of vegetation at ecotones such as the prairie-forest border in Minnesota.

In 2006 each field was divided in half, and one half randomly chosen for periodic prescribed burning (a fire every other year). We anticipate that the burned half will continue succession to prairie grassland while the unburned half will become white pine stands if seed sources are nearby, or will otherwise undergo extremely slow succession to oaks.

本项观察性研究旨在阐明生态系统演替的动态过程。研究人员对20余块弃耕地内植物与放牧动物物种的数量、类群及丰度变化进行监测。这些样地此前均为农用耕地，后于不同历史时期被弃耕，期间未受人为干扰，任由植物通过土壤种子库萌发，或借助风力、动物携带的种子完成自然定植。为实现年度间定点一致性采样，研究者在各弃耕样地内设立了永久样带；沿这些样带设置的永久样地用于采集土壤养分（尤其是氮素）、植被丰度、物种组成以及草食动物种群数据。采样周期约为每6年一次。初始调查阶段，研究人员在23块样地中各采集了100个规格为1×0.5米的样方。纳入E014数据集的弃耕样地包括4、5、10、21、24、26、27、28、32、35、39、40、41、44、45、47、53、70、72、76、77号样地。22(B)、29(A)与69(C)号样地最初也被纳入E014数据集，但在研究启动后不久便被挪作其他用途。本实验于1983年与1989年由首席研究员约翰内斯·克诺普斯（Johannes Knops）与戴维·蒂尔曼（David Tilman）牵头建立。此前在CDR及其他区域开展的相关研究已证实，火频度在维持草原开阔地与草原-森林交界带的栎树稀树草原群落结构方面发挥着决定性作用。火制度会对部分物种产生抑制作用，同时惠及另一部分物种，并驱动光照与养分的动态变化，进而调控群落的功能属性与多样性水平。最终，火频度会与气候、氮沉降、土地利用以及生物入侵等因素共同作用，决定乔草相互作用的结果，以及明尼苏达州草原-森林交界带这类生态交错带的植被动态。2006年，各弃耕样地被均分为两个半区，其中一半被随机选取进行周期性计划火烧（每两年实施一次火烧）。我们推测，火烧半区将持续向草原群落演替；而未火烧半区若周边存在白松种源，则会发展为白松林；若无适宜种源，则会以极慢的速率向栎树林演替。