Mapped Trees in CRUI Land Use Project at Harvard Forest 1996-2006

Numerous variables related to land use disturbance and recovery processes influence forest composition, structure, and growth. We measured forest communities in six sites that were formerly plowed, pastured, or continuously forested woodlots in Prospect Hill to test predictions about species composition, stand structure, and productivity in response to agricultural land use legacies. A permanent 30 x 50 m plot gridded in 5 x 5 m sub-plots was established in each of the 6 sites. All trees at least 2.5 cm DBH (diameter at breast height, 1.3 m) were mapped visually in the field, marked with an aluminum tag, and their DBH recorded in summer 1996. Individual boles of multi-stemmed trees were measured separately and a composite single DBH was calculated. Standing dead trees were also mapped and their DBH recorded as well. The 1996 data were used to determine above ground woody biomass using allometric equations for individual trees. The permanent plots were re-surveyed ten years later in fall 2006. The status of each tree mapped in 1996 was recorded (alive, dead standing, dead fallen, forked) and DBH’s were re-measured. Additional trees that grew across the 2.5 cm DBH threshold during the ten-year period were mapped and their DBH’s measured. Composite diameters and above ground woody biomass were determined for forked trees as in 1996. The 2006 re-measurements were used to analyze changes in species composition, stand structure (density, diameter distribution), and mortality patterns among species and size classes, and to calculate net changes in above ground woody biomass across the ten-year period.诸多与土地利用干扰及恢复过程相关的变量，会影响森林的群落组成、结构与生长动态。我们于展望山（Prospect Hill）的6处样地开展森林群落调查，这些样地此前分别为翻耕农田、放牧草场或持续保留的原生小片林地，旨在验证关于农业土地利用遗留效应下物种组成、林分结构与生产力的预测假说。在这6处样地中各设立一块尺寸为30×50米的永久样地，并以5×5米为间隔划分为若干子样方。1996年夏季，我们对所有胸径（DBH, Diameter at Breast Height，即1.3米高度处直径）不小于2.5厘米的林木开展野外目视定位，并用铝制标签进行标记，同时记录其胸径数据。对于多茎干林木，我们分别测量其每根茎干的直径，并计算得到复合单株胸径。同时对枯立木开展定位并记录其胸径。基于1996年的调查数据，结合单株林木的异速生长方程，计算得到地上木本生物量。研究团队于十年后的2006年秋季对这些永久样地开展了重测调查。记录1996年已定位的每株林木的存活状态（存活、枯立、枯倒、分叉），并重新测量其胸径。对这十年间胸径增长至2.5厘米阈值以上的新增林木开展定位并测量其胸径。与1996年的处理方式一致，对分叉林木计算其复合直径与地上木本生物量。利用2006年的重测数据，我们分析了物种组成、林分结构（密度、径级分布）的变化，以及不同物种与径级组的死亡模式，并计算了十年间地上木本生物量的净变化量。