Root biomass carbon and nitrogen: Old-Field Chronosequence: Plant Productivity

The goal of this research is to study the change in plant growth and species distribution during succession. Annual plant growth above ground is annually sampled in more than 20 fields from 4 permanently marked 3m x 4m plots in each field. 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. The fields included in this study are 4, 5, 10, 24, 26, 28, 35, 39, 41, 45, 53, 70, 72, 77 and the Lawrence strip that was abandoned in 1988. This experiment was started in 1987 by lead investigators David Tilman and Johannes Knops. In 2001 new sampling was started in positions similar to the E054 plots in these E014 fields: 21, 27, 32, 40, 44, 47, 76.

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.

本研究旨在探究群落演替（succession）过程中植物生长与物种分布的变化规律。研究人员每年对20余块样地开展采样，调查每块样地内4个永久标记的3m×4m样方中的地上一年生植物生长情况。这些样地此前均为耕地，后于不同历史时期被弃耕，并保持无干扰状态，以供土壤中留存的种子，或是经风力、动物携带进入样地的外来种子萌发并完成定居。
本研究涵盖的样地编号为4、5、10、24、26、28、35、39、41、45、53、70、72、77，以及1988年弃耕的Lawrence样带（Lawrence strip）。该实验于1987年由首席研究员David Tilman与Johannes Knops发起。2001年，研究人员在编号为21、27、32、40、44、47、76的E014类样地中，参照E054样方的设置方式启动了新的采样工作。
此前在CDR及其他区域的研究已证实，火频度在维持稀树草原（prairie）开阔生境与栎树稀树草原（oak savanna）于稀树草原-森林交界带的过程中起到决定性作用。火干扰制度（fire regimes）会对部分物种产生抑制作用，同时促进另一部分物种的生存，并调控光照与养分动态，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等因素相互作用，共同决定树-草互作的结局，以及明尼苏达州稀树草原-森林交界带等生态交错带（ecotones）的植被动态。
2006年，每块样地均被均分为两个区域，并随机选取其中一半进行周期性计划火烧（prescribed burning，每两年火烧一次）。研究团队预计，火烧区域将继续演替为稀树草原草本群落；未火烧区域若周边存在种子种源，则会逐步形成白松林，否则将以极慢的速率演替为栎树林。