Ants and Ecosystem Function in Hemlock Removal Experiment at Harvard Forest since 2006

Eastern hemlock (Tsuga canadensis) is a foundation species in eastern North American forests. Hemlock stands host unique assemblages of flora and fauna, and the structure of these assemblages is expected to change as hemlock declines due to infestation by the hemlock woolly adelgid (Adelges tsugae) and is removed by pre-emptive salvage logging. A 2003 survey of hemlock stands in central Connecticut and Massachusetts showed that ant species richness and abundance is substantially greater in logged and adelgid-infested hemlock stands than it is in intact hemlock stands (see HF065) and we hypothesized that we would see similar changes in ant species diversity following application of treatments in the Hemlock Removal Experiment at the Simes Tract (see HF118). We further hypothesized that because ants are known to modulate ecosystem function in other habitats that observed changes in ant species diversity would be accompanied by changes in ecosystem processes including soil respiration rate and nitrogen availability. In April 2006, we established a set of sub-plots in all eight canopy manipulation plots of the Hemlock Removal Experiment. In each canopy manipulation plot, we installed two ant exclosure plots, two disturbance control plots, and two control plots. Ant species richness and abundance, as well as effectiveness of the exclosures, is monitored with pitfall traps monthly during the summer. Soil nitrogen availability is measured using resins that are collected every three months, and soil respiration is measured bi-weekly during the growing season.东部铁杉（Tsuga canadensis）是北美东部森林的建群种（foundation species）。铁杉林孕育着独特的动植物群落，而随着铁杉因铁杉球蚜（Adelges tsugae）侵染发生衰退，且通过预防性灾后采伐（pre-emptive salvage logging）移除受灾林木后，此类群落的结构预计将发生改变。2003年对康涅狄格州中部与马萨诸塞州境内铁杉林开展的调查显示，经采伐且受球蚜侵染的铁杉林内，蚂蚁物种丰富度与个体丰度均显著高于未受干扰的原始铁杉林（详见数据集HF065），据此我们提出假设：在赛姆斯地块（Simes Tract）开展的铁杉移除实验中，施加相关处理后，蚂蚁物种多样性亦会呈现类似变化（详见数据集HF118）。我们进一步假设：鉴于蚂蚁在其他生境中可调控生态系统功能，因此观测到的蚂蚁物种多样性变化，将伴随土壤呼吸速率、氮素有效性等生态系统过程的改变。2006年4月，我们在铁杉移除实验的全部8个冠层操控样地中设立了一组副样地。在每个冠层操控样地内，我们分别布设2个蚂蚁排除样地（ant exclosure plots）、2个干扰对照样地（disturbance control plots）以及2个对照样地（control plots）。夏季每月利用陷阱诱捕器（pitfall traps）监测蚂蚁物种丰富度、个体丰度以及排除装置的有效性。土壤氮素有效性通过树脂法测定，树脂样品每3个月采集一次；土壤呼吸速率则在生长季期间每两周测定一次。