Community and Ecosystem Impacts in Hemlock Removal Experiment at Harvard Forest 2003-2020

Hemlock decline in New England is caused by direct and indirect effects of invasion of the hemlock woolly adelgid. Direct damage from the insect is causing gradual mortality of hemlock, and widespread harvesting of hemlock in advance of mortality creates a contrasting disturbance. Although both processes affect thousands of acres of forest annually, we have only a limited understanding of their effects on forest ecosystem function and productivity and the nature of the subsequent forest community. We anticipate that harvesting will yield different consequences than gradual mortality from the insect. Therefore we have designed an experiment to simulate the impact of both in order to contrast them. To simulate some of the effects of the adelgid (e.g., progressive mortality, retention of the wood on the site) we are girdling all hemlocks in a hemlock-dominated stand. In the adjacent area we are conducting a commercial harvesting of hemlock. Results from both experimental treatments will be compared to the changes observed in forests that are being infested by the adelgid, and can also be included in integrated analyses of a suite of large experiments that form a core component of the Harvard Forest LTER program.

新英格兰地区的铁杉林衰退，由铁杉球蚜（hemlock woolly adelgid）入侵带来的直接与间接效应共同引发。该昆虫造成的直接损伤正导致铁杉逐步死亡，而在树木死亡前开展的大规模铁杉采伐则带来了与之形成鲜明对比的干扰过程。尽管这两类过程每年均会波及数千英亩的森林，但目前我们对二者对森林生态系统功能、生产力以及后续森林群落特征的影响认知仍较为有限。我们推测，采伐作业与该昆虫引发的逐步死亡将带来截然不同的生态后果。因此，我们设计了一项实验以模拟这两类过程的影响，进而开展对比研究。为模拟铁杉球蚜的部分影响（例如逐步死亡、枯木留存于林地），我们对以铁杉为优势种的林分中的所有铁杉植株进行了环割处理。在相邻的林分中，我们则开展了商业化铁杉采伐作业。本研究两项实验处理的结果，既可以与受铁杉球蚜侵染的森林中观测到的变化进行对比，同时也可被纳入构成哈佛森林长期生态研究（Long-Term Ecological Research, LTER）计划核心组成部分的一系列大型实验的整合分析当中。