Crown dynamics and wood production of Douglas-fir trees in an old-growth forest
Crown dynamics and wood production of Douglas-fir trees in an old-growth forest
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DOI：
10.1016/j.foreco.2016.10.047
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发表时间：
2017-01
影响因子：
3.7
通讯作者：
H. Ishii;S. C. Sillett;Allyson L. Carroll
中科院分区：
文献类型：
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作者：
H. Ishii;S. C. Sillett;Allyson L. Carroll
大树是古老森林最突出的结构特征，被认为是全球重要的碳汇。由于它们的体积大，对大树的生物量和生长的估计往往是基于地面测量（例如，胸径），而对树冠内的生长动态知之甚少。随着树木的尺寸增加，树冠的生长可能不会反映在胸径测量中，从而导致地上森林生产力的不准确性。在这里，我们提出了一个10年的重新测量的树冠结构和分支/树干生长的400岁的黄杉menziesiitrees在西部华盛顿，美国古老的森林数据。在六个研究树木，40-60%的分支发生在上三分之一的活冠。10年以上的分支死亡率在树冠的下三分之一最高。活枝团（包括叶团）中，41-78%发生在活冠的中间三分之一。在研究期间，在树冠的上半部分，活枝质量增加，并且由于破碎或死亡而几乎没有损失。与此相反，活枝质量的增量可以忽略不计，活枝质量下降，在树冠的下半部分。平均而言，70-99%的每株树的活枝质量的增量发生在树冠的上半部分。从不同高度取的岩芯样品表明，树干变得不那么锥形随着年龄的增加，在最近10年的结果更大的增量上干半径。活枝质量增量分别占全株和树冠上部质量增量的42%和66%，其垂直分布与叶质量密度的垂直分布相一致。树干干重的增加量占下部树冠生长量的88%。在较低高度采集的岩心样品中，没有反映出树冠的生长增量。我们的估计的树干，分支，叶质量始终小于那些使用经验的异速生长方程的基础上胶带缠绕测量的胸径计算。此外，叶质量下降，在四棵树，而异速生长方程预测增加。我们的结果表明，大P. menziesiitrees可以维持木材的大量生产，特别是在树干和树枝的上部冠，而叶质量的变化可以更动态，这种增长动态的冠是很难通过DBH为基础的测量检测。
Large trees are the most prominent structural features of old-growth forests, which are considered to be globally important carbon sinks. Because of their large size, estimates of biomass and growth of large trees are often based on ground-level measurements (e.g., diameter at breast height, DBH) and little is known about growth dynamics within the crown. As trees increase in size, growth of the crown may not be reflected in DBH measurements contributing to inaccuracy of aboveground forest productivity. Here we present data from a 10-yr re-measurement of crown structure and branch/trunk growth of 400-year-oldPseudotsuga menziesiitrees in an old-growth forest in western Washington, USA. In six study trees, 40–60% of branches occurred in the upper third of the live crown. Branch mortality over 10 years was highest in the lower third of the crown. Of live-branch mass (including leaf mass), 41–78% occurred in the middle third of the live crown. During the study period, live-branch mass increased in the upper half of the crown and there was little loss due to fragmentation or death. In contrast, increment of live-branch mass was negligible and live-branch mass decreased in the lower half of the crown. On average, 70–99% of the increment of live-branch mass per tree occurred in the upper half of the crown. Core samples taken from various heights indicated that trunks became less tapered with increasing age as a result of greater increments of upper-trunk radius during the most recent 10 years. Increment of live-branch mass contributed 42 and 66% of the whole-tree and upper-crown increments of mass, respectively, and its vertical distribution corresponded to that of leaf mass density. Increments of trunk mass contributed 88% of the lower-crown increment. Growth increments of the crown were not reflected in core samples taken at lower heights. Our estimates of trunk, branch, and leaf mass were consistently smaller than those calculated using empirical allometric equations based on tape-wrap measurements of DBH. Moreover, leaf mass decreased in four trees, whereas allometric equations predicted increases. Our results indicate that largeP. menziesiitrees can sustain wood mass production, especially in trunk and branches of the upper crown, while leaf mass change can be more dynamic, and that such growth dynamics of the crown are difficult to detect via DBH-based measurements.