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 world-wide. 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直径呈现缩放关系，进而塑造森林生态系统的结构与功能。阐明此类缩放关系的机制基础，是理解全球森林及其在地球气候变化系统中作用的核心要务。本研究以美国弗吉尼亚州史密森尼保护生物学研究所的CTFS-ForestGEO温带混龄落叶林森林动态样地为研究对象，对9个变量的缩放关系开展理论预测验证，并将观测得到的缩放参数与全球其他森林的同类参数进行对比。研究涵盖15个物种与多种环境条件。树木的结构、生理与生态性状随树干直径的缩放模式，部分契合现有理论预测；相较于单一普适缩放值的理论，多数情况下更符合预测缩放值区间的理论。不同物种间的缩放关系存在显著差异，体现了实质性的生态分异。缩放关系亦随环境条件发生显著改变。例如，液流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则显著影响茎秆丰度的缩放模式。由此可见，林分水平的时间平均缩放关系（如直径生长量的缩放），其底层支撑是多样的物种水平缩放关系，而后者可随环境波动发生显著变化。若要运用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，我们亟需更精细化地理解制约林分水平缩放的各类因素，以及不同物种与环境条件下缩放变异的复杂性。