The motion of trees in the wind: a data synthesis
The motion of trees in the wind: a data synthesis
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DOI：
10.5194/bg-18-4059-2021
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发表时间：
2021-07-06
期刊：
影响因子：
4.9
通讯作者：
Gardiner, Barry
中科院分区：
文献类型：
--
作者：
Jackson, Toby D.;Sethi, Sarab;Gardiner, Barry
风和树木之间的相互作用控制着大气和森林树冠之间的能量交换。这种能量交换可能导致树木大面积受损，而风是世界上许多森林的主要干扰因素。然而，关于这一主题的大多数研究都集中在风险管理在经济上很重要的针叶林，而不是主导森林碳循环的阔叶林。本研究收集了树木运动时间序列数据，系统地评估了影响树木对风荷载响应的因素，包括森林和开阔环境中阔叶树和针叶树的数据。我们发现树木运动的两个最具描述性的特征是：(a)基频，这是树木摇摆速度的度量，与树的高度密切相关；(b)功率谱的斜率，这与从风到树的能量传递效率有关。有趣的是，在这项研究中，所有树木的功率谱斜率从中等到高风速都保持不变。这表明，与某些预测相反，阻尼或放大机制在高风速下不会发生显著变化，因此风害风险与风速的关系相对简单。针叶树对风荷载的响应不同于阔叶树。其中，针叶树的基频与大小有关，采用悬臂梁模型（即质量垂直分布），而阔叶树的基频更适合采用单摆模型（即以树冠为主）。针叶林的功率谱斜率也更陡。我们将这些发现解释为与树形结构密切相关；也就是说，针叶树由于其顶端优势，通常具有简单的形状，而阔叶则表现出更广泛的结构范围和更多的优势冠。
Interactions between wind and trees control energy exchanges between the atmosphere and forest canopies. This energy exchange can lead to the widespread damage of trees, and wind is a key disturbance agent in many of the world's forests. However, most research on this topic has focused on conifer plantations, where risk management is economically important, rather than broadleaf forests, which dominate the forest carbon cycle. This study brings together tree motion time-series data to systematically evaluate the factors influencing tree responses to wind loading, including data from both broadleaf and coniferous trees in forests and open environments.We found that the two most descriptive features of tree motion were (a) the fundamental frequency, which is a measure of the speed at which a tree sways and is strongly related to tree height, and (b) the slope of the power spectrum, which is related to the efficiency of energy transfer from wind to trees. Intriguingly, the slope of the power spectrum was found to remain constant from medium to high wind speeds for all trees in this study. This suggests that, contrary to some predictions, damping or amplification mechanisms do not change dramatically at high wind speeds, and therefore wind damage risk is related, relatively simply, to wind speed.Conifers from forests were distinct from broadleaves in terms of their response to wind loading. Specifically, the fundamental frequency of forest conifers was related to their size according to the cantilever beam model (i.e. vertically distributed mass), whereas broadleaves were better approximated by the simple pendulum model (i.e. dominated by the crown). Forest conifers also had a steeper slope of the power spectrum. We interpret these finding as being strongly related to tree architecture; i.e. conifers generally have a simple shape due to their apical dominance, whereas broadleaves exhibit a much wider range of architectures with more dominant crowns.