Overstory Mapped Tree Plots at Harvard Forest since 1990

These plots were established and mapped in 1990 for an experiment designed to study the effects of selective overstory tree mortality. The planned manipulation was to kill and leave standing one species in each of four plots, to simulate mortality by a species-specific pathogen. This manipulation was never done, for logistical reasons and because the appearance of the hemlock woolly adelgid provided a more pressing "natural" experiment to study; however, the plots are maintained and have been used in other studies. There are four 50m x 50m plots, located in a mixed hardwood forest (red oak and maple species are major components), north of the experimental hurricane. Tree data from the control plot of the experimental hurricane study could be added to this set for some analyses, since all the plots are in the same general area and forest type, and similar types of measurements were made on all of these trees. Tree diameter and condition were re-surveyed in these plots in Autumns 2003 and 2013, and saplings growing into the "tree" size class of greater than or equal to 5cm diameter were measured, tagged and mapped.

这些样地于1990年建立并完成绘图，旨在开展一项研究选择性上层林木死亡效应的实验。原计划干预措施为：在四个样地中各杀死并保留一个树种的立木，以模拟物种特异性病原体导致的死亡事件。然而，由于后勤因素，且铁杉球蚜的出现提供了更紧迫的“自然”实验研究契机，该干预措施从未实施；但样地仍得到维护，并已用于其他研究。样地共四块，每块尺寸为50m×50m，位于实验飓风研究区域以北的混合硬木林（红橡与枫树为主要成分）中。实验飓风研究的对照样地树木数据可添加至本数据集用于部分分析——因所有样地处于同一区域、同一林型，且树木测量类型相似。2003年和2013年秋季，研究人员重新调查了这些样地的树木直径与健康状况，并对进入“树木”尺寸等级（直径≥5cm）的幼树进行了测量、标记与绘图。