Data from: Size-related scaling of tree form and function in a mixed-age forest

Many morphological, physiological, and ecological traits of trees scale with diameter, shaping the structure and function of forest ecosystems. Understanding the mechanistic basis for such scaling relationships is key to understanding forests globally and their role in Earth's changing climate system. Here, we evaluate theoretical predictions for the scaling of nine variables in a mixed-age temperate deciduous forest (CTFS-ForestGEO forest dynamics plot at the Smithsonian Conservation Biology Institute, Virginia, USA) and compare observed scaling parameters to those from other forests worldwide. We examine fifteen species and various environmental conditions. Structural, physiological, and ecological traits of trees scaled with stem diameter in a manner that was sometimes consistent with existing theoretical predictions—more commonly with those predicting a range of scaling values than a single universal scaling value. Scaling relationships were variable among species, reflecting substantive ecological differences. Scaling relationships varied considerably with environmental conditions. For instance, the scaling of sap flux density varied with atmospheric moisture demand, and herbivore browsing dramatically influenced stem abundance scaling. Thus, stand-level, time-averaged scaling relationships (e.g., the scaling of diameter growth) are underlain by a diversity of species-level scaling relationships that can vary substantially with fluctuating environmental conditions. In order to use scaling theory to accurately characterize forest ecosystems and predict their responses to global change, it will be critical to develop a more nuanced understanding of both the forces that constrain stand-level scaling and the complexity of scaling variation across species and environmental conditions.

树木的诸多形态、生理及生态性状均随茎直径呈现异速缩放规律，这直接塑造了森林生态系统的结构与功能。阐明此类尺度缩放关系的机制基础，是全球尺度解析森林及其在地球气候变化系统中作用的核心要务。本研究针对美国弗吉尼亚州史密森尼保护生物学研究所（Smithsonian Conservation Biology Institute）的CTFS-ForestGEO温带混龄落叶林森林动态样地，对9个变量的尺度缩放关系的理论预测开展验证，并将实测得到的缩放参数与全球其他森林的对应参数进行对比。研究涵盖15个树种与多种环境条件。树木的结构、生理及生态性状随茎直径的缩放模式，部分与现有理论预测相符；相较于单一普适性缩放值的预测，多数情况更符合支持缩放值存在区间的理论预测。不同树种间的尺度缩放关系存在显著差异，这反映了物种间实质性的生态分异。尺度缩放关系亦随环境条件发生显著变化。例如，树液通量密度的缩放关系随大气水汽需求发生变化，而植食性动物的啃食会显著影响茎秆丰度的缩放关系。因此，林分水平的时间平均尺度缩放关系（如直径生长的缩放关系），其底层支撑机制是多样的物种水平缩放关系，而这些关系可随环境波动发生显著改变。若要借助尺度缩放理论精准表征森林生态系统，并预测其对全球变化的响应，就必须更细致地理解约束林分水平缩放的各类因素，以及不同物种与环境条件下的尺度缩放变异复杂性。