Deer and Moose Browsing in Hemlock Removal Experiment at Harvard Forest 2008

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. 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. Deer and moose foraging can play a key role in shaping forest regeneration after disturbance in temperate forest. In 2008, we initiated a browsing survey of woody stems in the Simes hemlock removal experiment plots. There are regular moose sightings in the study area, and moose pellets are commonly found within the plots. Also, extensive browsing of tree regeneration in the logged plots was Noted starting in 2007.新英格兰地区的铁杉林衰退，由铁杉球蚜（hemlock woolly adelgid）入侵引发的直接与间接效应共同导致。该昆虫造成的直接危害，正逐步引发铁杉植株死亡；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，会直接造成植株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，但我们对其对森林生态系统功能、生产力以及后续森林群落的特征与动态的影响仍所知有限。我们推测，采伐干扰与该昆虫引发的逐步死亡所带来的生态后果存在显著差异。因此，我们设计了一项实验，通过对铁杉林分实施采伐（logging）或环剥（girdling）来模拟这两种截然不同的干扰类型。本实验处理的结果，将与受铁杉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框架中——这些实验是哈佛森林（Harvard Forest）长期生态研究（Long-Term Ecological Research, LTER）计划的核心组成部分。在温带森林的干扰后，鹿与驼鹿的觅食行为对森林更新格局起着关键的调控作用。2008年，我们启动了针对Simes铁杉移除实验样地内木本茎秆的啃食调查。研究区域内常有驼鹿活动踪迹被观测到，且样地内也频繁发现驼鹿粪便。此外，2007年起研究人员便观测到采伐样地内的树木更新受到了严重啃食。