Data from: Tropical tree species diversity in a mountain system in southern Mexico: local and regional patterns and determinant factors

Mechanisms explaining patterns of biodiversity along elevation gradients in tropical mountain systems remain controversial. We use a set of climatic, topographic and soil variables encompassing regional, landscape and local-level spatial scales to explain the spatial variation of tree species diversity in the Sierra Madre of Chiapas, Mexico. We sampled 128 circular plots (0.1-ha each) in four elevational bands along four elevation gradients or transects encompassing 100-2200 m. A total of 12,533 trees belonging to 444 species were recorded. Diversity patterns along the elevation gradient and the explanatory power of independent variables were dependent on spatial scale (regional vs transect) and functional group (total vs late-successional or pioneer species). Diversity of all species and late-successional species (1 - proportion of pioneer species) showed a constant pattern at the regional and transect scales, with low predictive power of climatic variables and/or elevation. A linear decrease of either number or proportion of pioneer species diversity was observed with increasing elevation, which was correlated with temperature, rainfall, and human disturbance trends. Total species diversity showed an increase with rainfall of the warmest quarter, indicating a regional-level limiting effect of seasonality (drought duration). Yet the explanatory power of climatic and topographic variables was higher at the individual transect level than at the regional scale, suggesting the parallel but differential influence of evolutionary and geological history factors on diversification not so far studied to explain elevation patterns of species diversity in tropical mountain systems.

热带山地系统沿海拔梯度（elevation gradients）的生物多样性分布格局背后的解释机制仍存在争议。本研究采用涵盖区域、景观与局地三级空间尺度（spatial scales）的气候、地形及土壤变量，旨在解析墨西哥恰帕斯州马德雷山脉内树木物种多样性的空间变异规律。我们沿四条覆盖100至2200米海拔梯度的样带（transects），在四个海拔带内布设了128个圆形样地（单个样地面积为0.1公顷）。本次调查共记录到12533株树木，隶属于444个物种。沿海拔梯度的多样性分布格局以及自变量的解释能力，取决于空间尺度与功能群类型：前者分为区域尺度与样带尺度，后者分为全部物种、后期演替物种（late-successional species）或先锋物种（pioneer species）。在区域与样带尺度下，全部物种与后期演替物种（即1减去先锋物种占比）的多样性均呈现稳定的分布格局，气候变量及/或海拔的预测能力较低。先锋物种多样性的数量或占比随海拔升高呈线性下降趋势，且该趋势与气温、降水及人为干扰强度相关联。全部物种多样性随最暖季度降水量的增加而升高，这表明季节动态（干旱持续时长）在区域尺度上存在限制效应。但气候与地形变量在单个样带尺度上的解释能力高于区域尺度，这表明演化与地质历史因素对物种分化存在平行但差异化的影响——这类影响目前尚未被充分研究，以用于解释热带山地系统中物种多样性沿海拔梯度的分布格局。