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）是建群种。由于入侵物种铁杉球蚜（Adelges tsugae）的危害以及预防性抢救性采伐，森林中的铁杉逐渐消失，与之相伴的物种组合结构预计将发生改变。我们在新英格兰的一处森林中以公顷尺度操控铁杉林冠结构，旨在探究铁杉死亡对蚂蚁、甲虫及蜘蛛类群组合的影响。相较于参照铁杉林分，铁杉原位死亡以及采伐移除铁杉均改变了甲虫和蜘蛛的群落组成与多样性，而采伐提升了蚂蚁类群组合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类群组成并非随机，但我们未发现证据表明，无论在操控处理林分还是未受干扰的林分中，种间竞争均塑造了蚂蚁、甲虫或蜘蛛的类群结构。铁杉介导的环境过滤似乎维持了林分中较低的物种丰富度与均匀度水平，这表明因铁杉球蚜或人类活动导致的铁杉丧失，不太可能在局域尺度上造成蚂蚁、甲虫或蜘蛛物种的局部灭绝。