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衰退，由铁杉球蚜（hemlock woolly adelgid）入侵带来的直接与间接效应所引发。该昆虫造成的直接损伤会引发铁杉的渐进式死亡；与之相对，在树木死亡前开展的大规模铁杉采伐，则会导致立木快速死亡，并将生物量从样地中移除。尽管这两种过程每年都会影响数千英亩的森林，但我们对其如何影响森林生态系统功能与生产力，以及后续森林群落的特征，仍所知有限。我们推测采伐与该昆虫引发的渐进式死亡会带来截然不同的后果，因此设计了一项实验，通过对铁杉林分进行环割（girdling）或采伐来模拟这两种相反的干扰效应。本实验的处理结果，将与受铁杉球蚜侵染的森林中观测到的变化进行对比，同时也可纳入一系列大型实验的整合分析中——这些实验是哈佛森林长期生态研究（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会对森林更新过程起到关键塑造作用。2008年，我们在赛姆斯（Simes）铁杉移除实验样地中启动了木本茎秆的啃食调查。研究区域内常有驼鹿活动踪迹被记录，且样地内也频繁发现驼鹿粪粒。此外，2007年起研究人员便观察到采伐样地内的树木更新受到了广泛的啃食干扰。