Species Abundance Distributions (SADs) for local tree communities in 1-ha forest plots on 20 tropical islands in the Indo-Pacific region

Tree species abundance data (i.e., the number of individuals for each tree species within a community), was obtained for 51 1-ha plots in humid tropical forests on 20 islands (13 archipelagos) in the Indo-Pacific region. Only plots without any evidence of recent natural or anthropogenic disturbances were conisidred (e.g., secondary forest plots, as defined by the author of source data, were removed). In each plot, all trees with a stem diameter ≥ 10 cm at c. 1.3 m above the base (DBH, diameter at breast height) were identified. All plots were located in lowland forests on islands larger than 1 km2. For each plot the number of trees (N), the number of tree species (R), and the shape parameter α of the gambin model (which characterize the shape of species abundance distributions, SADs) were computed. Standaridized R (Rstand) and α (αstand) were also computed by randomly subsampling 400 trees per plot before counting the number of species and fitting gambin models. This process was repeated 100 times for each plot before estimating Rstand and αstand as the mean value of Ri and αi from all iterations. Island area (Area) and isolation (Dist) were extracted from the Island Directory (http://islands.unep.ch), mean annual temperature (MAT) and mean annual precipitation (MAP) were extracted for each plot location from CHELSA (http://chelsa-climate.org/) and a power dissipation index (PDI), a proxy of the energy released by cyclones, was computed using the IBTrACs database (https://www.ncdc.noaa.gov/ibtracs/, see Knapp, Kruk, Levinson).

本数据集涵盖印太地区20个岛屿（隶属于13个群岛）的湿润热带森林中51块1公顷样地的乔木树种多度数据（即群落内各乔木树种的个体数量）。仅纳入无近期自然或人为干扰迹象的样地，例如源数据作者定义的次生林样地已被排除。在每块样地中，所有基干以上约1.3米处茎直径≥10厘米的乔木（即胸径DBH，Diameter at Breast Height）均完成物种鉴定。所有样地均位于面积大于1平方千米的岛屿的低地森林中。针对每块样地，计算了乔木总个体数（N）、乔木物种数（R）以及描述物种多度分布（Species Abundance Distributions，简称SADs）形态的gambin模型（gambin model）形状参数α。此外，通过对每块样地随机抽取400株乔木，随后统计物种数并拟合gambin模型，计算得到标准化物种数（Rstand）与标准化形状参数（αstand）。该过程对每块样地重复100次后，以所有迭代得到的物种数Ri与参数αi的均值作为最终的Rstand与αstand。岛屿面积（Area）与隔离度（Dist）数据取自《岛屿名录》（http://islands.unep.ch）；样地所在区域的年平均气温（MAT，Mean Annual Temperature）与年平均降水量（MAP，Mean Annual Precipitation）数据取自CHELSA气候数据集（http://chelsa-climate.org/）；同时以IBTrACS数据库（https://www.ncdc.noaa.gov/ibtracs/, 参见Knapp、Kruk与Levinson的研究）为数据源，计算得到气旋释放能量的替代指标——功率耗散指数（PDI，Power Dissipation Index）。