Maximum plant height along transects: 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.

本观测性研究（observational study）旨在阐明生态系统演替（ecosystem succession）的动态过程。研究团队对20余块弃耕农田中植物与植食性动物物种的数量、类群及丰度变化进行了长期监测。这些农田此前均经耕作，后于历史不同时期弃耕。弃耕后农田不再受人为干扰，以供土壤种子库中的种子，或经风力、动物传播至农田的外来种子萌发并发育为植被。研究人员在这些弃耕农田中布设了永久样带（permanent transects），以确保每年均可在同一固定点位开展采样工作。沿样带布设的永久样方（permanent plots）则用于采集土壤养分（尤其针对氮素）、植被丰度、物种组成以及植食动物种群相关数据。采样工作每约6年开展一次。初始调查阶段，研究人员对23块农田各布设100个尺寸为1m×0.5m的样方（quadrats）进行采样。纳入E014数据集的弃耕农田编号为4、5、10、21、24、26、27、28、32、35、39、40、41、44、45、47、53、70、72、76、77。编号为22(B)、29(A)与69(C)的农田最初也被纳入E014数据集，但在研究启动后不久便被挪作他用。本实验由首席研究员约翰内斯·克诺普斯（Johannes Knops）与戴维·蒂尔曼（David Tilman）分别于1983年和1989年搭建完成。
CDR及其他地区的既往研究表明，火频度在维持林草交错带的草原开阔地与栎树稀树草原（oak savanna）中发挥着决定性作用。火制度（fire regimes）会对部分物种种群产生抑制作用，同时促进另一部分物种繁衍，并驱动光照与养分动态变化，进而影响群落功能特征与物种多样性水平。最终，火频度会与气候、氮沉降（N deposition）、土地利用及生物入侵（biotic invasion）共同作用，决定林木-草本植物互作的结果，以及明尼苏达州林草交错带等区域的植被动态。
2006年，研究团队将每块农田均分为两半，随机选取其中一半开展周期性控制性火烧（prescribed burning，每两年火烧一次）。研究预计，经火烧处理的一半农田将继续演替为草原草本群落；而未火烧的一半若周边存在白皮松种源，则会发展为白皮松林，否则将以极慢的速度演替为栎树群落。