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

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衰退，由铁杉球蚜（hemlock woolly adelgid）入侵引发的直接与间接效应所导致。该昆虫造成的直接损伤会引发铁杉的渐进式死亡，而在铁杉死亡前开展的大规模采伐则会形成与之截然不同的森林干扰。尽管这两种过程每年都会影响数千英亩的森林，但目前我们对其如何作用于森林生态系统功能、生产力，以及后续森林群落的特征的认知仍十分有限。我们推测，商业化采伐带来的生态后果与该昆虫引发的渐进式死亡存在显著差异。因此，我们设计了一项实验来模拟这两种过程的影响，以对比二者的差异。为模拟铁杉球蚜的部分影响（例如渐进式死亡、木材留存于林地），我们对以铁杉为优势种的林分中的所有铁杉进行了环割处理。在相邻的林分中，我们则开展商业化铁杉采伐作业。我们会将两种实验处理的结果，与受铁杉球蚜侵染的森林中观测到的变化进行对比；同时这些结果也可纳入一系列构成哈佛森林LTER计划核心组成部分的大型实验的整合分析当中。