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）是北美东部森林中的建群种（foundation species）。铁杉林孕育着独特的动植物类群，随着铁杉因铁杉球蚜（Adelges tsugae）侵染而衰退，加之通过预防性抢救性采伐移除受侵染植株，此类群的群落结构预计将发生改变。2003年针对康涅狄格州中部与马萨诸塞州铁杉林开展的调查显示，经采伐且受球蚜侵染的铁杉林内，蚂蚁的物种丰富度与个体丰度均显著高于未受干扰的完整铁杉林（详见HF065）；据此我们提出假说：在西姆斯地块的铁杉移除实验（Hemlock Removal Experiment）中，施加处理后蚂蚁物种多样性也会出现类似变化（详见HF118）。我们进一步提出假说：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，我们在该铁杉移除实验的全部8个冠层调控样地中设置了系列副样地；每个冠层调控样地内均布设2个蚂蚁排除样地、2个干扰对照样地及2个对照样地。夏季每月通过陷阱诱捕器（pitfall traps）开展监测，以统计蚂蚁物种丰富度与个体丰度，并验证蚂蚁排除装置的有效性。土壤氮素有效性采用树脂法测定，每3个月回收一次树脂；生长季期间每两周测定一次土壤呼吸速率。