Soil Arthropods in Hemlock Removal Experiment at Harvard Forest 2008

In eastern North American forests, eastern hemlock (Tsuga canadensis) is a foundation species. As hemlock is lost from forests due to the invasive hemlock woolly adelgid (Adelges tsugae) and pre-emptive salvage logging, the structure of assemblages of species associated with hemlock is expected to change. We manipulated hemlock canopy structure at hectare scales to investigate the effects of hemlock death on assemblages of ants, beetles, and spiders in a New England forest. Relative to reference hemlock stands, both in situ death of hemlock and logging and removal of hemlock altered composition and diversity of beetles and spiders, and logging increased the species richness and evenness of ant assemblages. Species composition of ant assemblages in disturbed habitats was non-random relative to the regional species pool, but we found no evidence that interspecific competition shaped the structure of ant, beetle or spider assemblages, in either manipulated or intact forest stands. Environmental filtering by hemlock appears to maintain low levels of species richness and evenness in forest stands, suggesting that the loss of hemlock due to the hemlock woolly adelgid or human activities will not likely lead to extirpations of ant, beetle, or spider species at local scales.

北美东部森林中，东部铁杉（Tsuga canadensis）为基础物种。受入侵害虫铁杉球蚜（Adelges tsugae）侵害以及预防性采伐伐除受侵林木的影响，森林中原生铁杉种群持续丧失，与之伴生的物种群落结构预计将发生显著改变。本研究在公顷尺度上对铁杉林冠结构进行人工调控，以探究铁杉死亡对新英格兰森林内蚂蚁、甲虫与蜘蛛群落的影响。相较于对照铁杉林分，铁杉原位死亡与采伐移除铁杉两种干扰方式均改变了甲虫和蜘蛛群落的物种组成与多样性，而采伐操作还显著提升了蚂蚁群落的物种丰富度与均匀度。相较于区域物种库，受干扰生境中的蚂蚁群落物种组成并非随机分布，但无论在调控处理林分还是未受干扰的原始林分中，均未发现种间竞争对蚂蚁、甲虫或蜘蛛群落结构存在塑造作用的证据。铁杉介导的环境过滤似乎维持了林分较低的物种丰富度与均匀度水平，这表明由铁杉球蚜或人类活动导致的铁杉丧失，大概率不会引发局地尺度下蚂蚁、甲虫或蜘蛛物种的局部灭绝。