Seed Bank in Hemlock Removal Experiment at Harvard Forest 2004-2010

The impending loss of hemlock trees due to hemlock woolly adelgid (Adelges tsugae) infestation prompted the need to identify species of plants able to colonize areas where hemlock has been removed. We investigated species present in the seed bank (in 2004 and 2010), the seedling bank (in 2004 and 2010), and seed rain (from 2005-2010) in the Harvard Forest Hemlock Removal Experiment. In 2004, Kelley Sullivan and Aaron Ellison determined the distribution of seeds buried in the soil in the six hemlock and two hardwood stands, before canopy treatments were applied (data files hf105-01, hf105-02). In 2010, Elizabeth Farnsworth and Aaron Ellison examined the distribution of plant species present five years after the simulated hemlock removal experiment was performed and six years after the baseline, pre-treatment study of the seedbank (data files hf105-03, hf105-04, hf105-05). In the 2010 study, we hypothesized that the composition of the seed and seedling banks and seed rain would diverge among the two treatments and the controls, based on the differential impacts of harvesting versus adelgid attack on the standing vegetation. We further hypothesized that the older (deeper) strata of the seedbanks of the treatment plots would have been exhausted over time, thus yielding poor germination relative to the top strata that continually receive seed rain. Identical methods of characterizing the composition of the seedbank and the aboveground vegetation at seedbank core locations were applied in both 2004 and 2010. Additional comparisons were made with long-term data collected on overall plant species composition in the Simes plots (datasets HF 106, HF126), and with data on seed rain (data file hf105-05). This study provides a unique temporal documentation of changes in the seedbank, seed rain, and vegetation under conditions of a changing overstory.

受铁杉球蚜（Adelges tsugae）侵染，铁杉林正濒临消亡，这使得学界亟需筛选可在铁杉被移除的区域成功定植的植物物种。本研究依托哈佛森林铁杉移除实验（Harvard Forest Hemlock Removal Experiment），对2004年与2010年的种子库（seed bank）、幼苗库（seedling bank），以及2005至2010年的种子雨（seed rain）中的植物物种展开了调查。2004年，Kelley Sullivan与Aaron Ellison在林冠处理实施前，对6个铁杉林样地与2个硬木林样地内土壤埋藏种子的分布情况开展了测定，对应数据集文件为hf105-01、hf105-02。2010年，Elizabeth Farnsworth与Aaron Ellison对模拟铁杉移除实验开展5年后、种子库基线预处理研究6年后的植物物种分布情况进行了调查，对应数据集文件为hf105-03、hf105-04、hf105-05。在2010年的研究中，基于采伐与球蚜侵染对现存植被的差异化影响，我们提出两项核心假设：其一，种子库、幼苗库与种子雨的群落组成会在两种处理组与对照组间出现显著分化；其二，随着时间推移，处理样地种子库中较老（深层）的土层会逐渐耗尽，因此相较于持续接收种子雨的表层土层，其萌发率会相对更低。2004年与2010年的研究均采用了相同的方法，对种子库核心样点处的种子库组成与地上植被特征进行表征。本研究还额外与两项长期数据集开展了对比：一是Simes样地内的植物物种组成整体长期监测数据（数据集编号：HF 106、HF126），二是种子雨监测数据（数据集文件：hf105-05）。本研究针对林冠层动态变化下的种子库、种子雨与植被变化情况，提供了独特的时间序列记录。