Litterfall in Hemlock Removal Experiment at Harvard Forest since 2005

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, in contrast, causes immediate mortality and removal of biomass from the site. 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 designed an experiment to simulate these contrasting impacts, by logging or girdling hemlock stands. Results from the 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）入侵所引发的直接与间接效应共同导致。该昆虫造成的直接损害会引发铁杉的渐进式死亡；与之形成鲜明对比的是，在铁杉自然死亡前开展的大规模采伐，会导致林木即时死亡并将样地内的生物量移除。尽管这两种干扰过程每年都会影响数千英亩的森林，但我们对其在森林生态系统功能、生产力以及后续森林群落特征方面的影响，仍仅有有限的认知。我们推测，采伐所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，通过对铁杉林分实施采伐或环剥（girdling）处理，来模拟这两种截然不同的干扰影响。本实验的处理结果，将与受该球蚜侵染的森林中观测到的动态变化进行对比，同时也可纳入一系列大型实验的整合分析当中——这些实验是哈佛森林长期生态研究（Long-Term Ecological Research, LTER）项目的核心组成部分。