Sapwood area~DBH allometries for 14 common tree species in a successional tropical forest in Thailand

Sapwood area is an important parameter for estimating canopy transpiration in the forest water cycle. However, sapwood area highly varies across species and forest ecosystems and is difficult to measure directly. Therefore, species- and site-specific allometric equations are needed to estimate the sapwood area of all trees in a forest. Here, we conducted a comprehensive campaign to measure sapwood thickness and to estimate the sapwood area of 14 common tree species in a successional forest in Thailand. These data represent the first comprehensive measurements of sapwood area in south-east Asian successional forests growing under diverse environmental conditions in terms of soil moisture and canopy density. The results show that a power function can significantly explain the relationship between sapwood area and stem size, represented by diameter at breast height (DBH), in all species in both primary and secondary forests. Interestingly, a single equation could describe the sapwood area~DBH relationship in all species and forest stages, except for Dipterocarpus gracilis, an emergent, dominant species in the primary forest. The latter showed slower growth in sapwood area once the trees reached a DBH of ~30 cm. Overall, our results can benefit future studies that estimate canopy transpiration of tropical forests with similar conditions as in our study sites.

边材面积（sapwood area）是估算森林水循环中林冠蒸腾量的关键参数。然而，边材面积在不同物种与森林生态系统间存在显著差异，且难以直接测定。因此，需构建物种与立地特异性的异速生长方程，以估算森林内所有树木的边材面积。本研究针对泰国一处演替森林中的14个常见树种，开展了全面的边材厚度测量与边材面积估算工作。该数据集是东南亚地区首个覆盖多样土壤湿度、林冠密度环境条件的演替森林边材面积综合测量结果。研究结果表明，无论是原始林还是次生林，所有树种的边材面积与以胸径（diameter at breast height, DBH）表征的茎干尺寸之间均存在显著的幂函数相关关系。值得注意的是，除纤细龙脑香（Dipterocarpus gracilis）——一种原始林中的上层优势树种——外，单一方程即可描述所有树种及林分演替阶段的边材面积与胸径间的关联。纤细龙脑香在树木胸径达到约30厘米后，边材面积的生长速率明显放缓。总体而言，本研究结果可为未来估算与本研究站点环境相似的热带森林林冠蒸腾量的相关研究提供重要参考。