Understory Removal Experiment at Harvard Forest 1956-2018

In 1956, Ernie Gould and colleagues established an experiment to test whether removing understory trees will accelerate the growth of the residual overstory. The motivation for the experiment was the suggestion that the understory uses growth materials that would otherwise be available for the main canopy crop trees, and that if the understory were removed the development of the crop trees would be accelerated. In Tom Swamp Compartment I, a 300’ by 400’ rectangular plot was established in a closed-canopy hardwood forest, and every tree >2 inches dbh was mapped, measured and assigned to the overstory or understory. In half of the plot, all understory trees and woody shrubs were cut. Wood and brush were removed from the study area. Sprouts that emerged were killed by spraying with 2-4-5-T and kerosene in 1956 and 1958. Diameter growth measurements of the remaining trees (overstory in the treated area; overstory and understory in the control) were repeated in 1960, 1966, 1969, and 1975 as part of the original experiment. The control portion of the plot was measured in 2003 and 2018. This data set contains tree measurements from the control portion of the site for 1956, 1969, 1975, 2003, and 2018. Additional measurements are available on paper data sheets in the Harvard Forest Document Archives (Research File HF 1956-03). Results of the understory removal experiment are reported in Kelty and Gould (1987).1956年，厄尼·古尔德（Ernie Gould）及其同事开展了一项实验，旨在验证移除林下树木是否会加速保留的上层林木的生长。该实验的设计初衷源于一项假说：林下植被会消耗本可供给主林冠主栽林木的生长资源，若移除林下植被，主栽林木的生长发育将得到加速。在汤姆沼泽分区I（Tom Swamp Compartment I）中，研究人员于一片郁闭阔叶林中划定一块300英尺×400英尺的矩形样地，对所有胸径（dbh）大于2英寸的树木进行测绘、测量，并划分为上层林木或下层林木。在该样地的一半区域中，所有林下树木与木本灌木均被移除，采伐所得的木材与灌丛被清离研究区域。1956年与1958年，研究人员通过喷施2-4-5-T与煤油的方式灭杀了萌生出的新芽。作为原始实验的一部分，研究人员分别于1960年、1966年、1969年及1975年对剩余树木的胸径生长量进行复测：处理组仅测量上层林木，对照组则同时测量上层与下层林木。该样地的对照组区域还分别于2003年与2018年完成了测量。本数据集包含该样地对照组在1956年、1969年、1975年、2003年及2018年的林木测量数据。额外的测量数据以纸质数据表的形式保存于哈佛森林档案库（Harvard Forest Document Archives，研究档案编号HF 1956-03）中。林下植被移除实验的相关研究结果已发表于Kelty与Gould（1987）的文献中。