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）。铁杉林支撑着独特的动植物群落，其群落结构预计将随铁杉因铁杉毛毡蚜（Adelges tsugae）侵染发生衰退，以及受侵染个体经预防性救助采伐被移除而发生改变。2003年对康涅狄格州中部与马萨诸塞州铁杉林的调查显示，经采伐或受蚜虫侵染的铁杉林内，蚂蚁物种丰富度与个体多度均显著高于完整未受干扰的铁杉林（详见HF065）；研究团队据此提出假说：在西姆斯地块（Simes Tract）开展的铁杉移除实验（详见HF118）中，施加相关处理后，蚂蚁物种多样性也会出现类似变化。研究团队进一步提出假说：鉴于蚂蚁在其他生境中已被证实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，研究团队在铁杉移除实验的全部8个冠层操控样地内设置了一批副样地，每个冠层操控样地内均布设2个蚂蚁排除样地（ant exclosure plots）、2个干扰对照样地与2个空白对照样地。夏季每月采用陷阱诱捕器（pitfall traps）开展监测，内容包括蚂蚁物种丰富度、个体多度以及蚂蚁排除装置的有效性；土壤氮素有效性通过树脂法测定，树脂样品每3个月收集一次；土壤呼吸速率则在生长季期间每两周测定一次。