College of Life Sciences, Zhejiang University, Hangzhou, 310029, China.
College of Environmental & Resource Sciences, Zhejiang University, Hangzhou, Zhejiang, 310058, China.
Am J Bot. 2022 Jul;109(7):1097-1107. doi: 10.1002/ajb2.16023. Epub 2022 Jul 22.
Competition is an important driver of tree mortality and thus affects forest structure and dynamics. Tree architectural traits, such as height-to-diameter (H-D) and branch length-to-diameter (L-d) relationships are thought to influence species competitiveness by affecting light capture. Unfortunately, little is known about how the H vs. D and L vs. d scaling exponents are related to tree performance (defined in the context of growth vigor) in competition.
Using data from field surveys of 1547 individuals and destructive sampling of 51 trees with 1086 first-order branches from a high-density Pinus massoniana forest, we explored whether the H vs. D and the L vs. d scaling exponents respectively differed numerically across tree performance and branch vertical position in crowns.
The results indicated that (1) the H vs. D scaling exponent decreased as tree performance declined; (2) the L vs. d scaling exponent differed across tree performance classes (i.e., the scaling exponent of "inferior" trees was significantly larger than that of "moderate" and "superior" trees); (3) the L vs. d scaling exponent decreased as branch position approached ground level; and (4) overall, the branch scaling exponent decreased as tree performance improved in each crown layer, but decreased significantly in the intermediate layer.
This study highlights the variation within (and linkage among) length-to-diameter scaling relationships across tree performance at the individual and branch levels. This linkage provides new insights into potential mechanisms of tree growth variation (and even further mortality) under competition in subtropical forests.
竞争是树木死亡的一个重要驱动因素，因此会影响森林的结构和动态。树木的结构特征，如高径比（H-D）和枝长径比（L-d）关系，被认为通过影响光捕获而影响物种竞争力。然而，对于 H 与 D 的比值和 L 与 d 的比值的比例指数与竞争中树木的性能（在生长活力的背景下定义）之间的关系，人们知之甚少。
利用来自高密度马尾松林实地调查的 1547 个个体的数据和对 51 棵树的破坏性采样数据，其中 1086 个一级树枝，我们探讨了 H 与 D 的比例指数和 L 与 d 的比例指数是否分别在树冠中树木性能和树枝垂直位置上数值上有所不同。
结果表明：（1）随着树木性能的下降，H 与 D 的比例指数减小；（2）L 与 d 的比例指数在树木性能类别之间存在差异（即，“较差”树木的比例指数明显大于“中等”和“较好”树木）；（3）随着树枝位置接近地面，L 与 d 的比例指数减小；（4）总体而言，在每个树冠层中，随着树木性能的提高，树枝比例指数减小，但在中层显著减小。
本研究强调了个体和树枝水平上树木性能内（和之间）长度与直径比例关系的变化。这种联系为在亚热带森林中竞争下树木生长变化（甚至进一步死亡）的潜在机制提供了新的见解。
