1 Environmental Change Institute, School of Geography and the Environment, University of Oxford , Oxford OX1 3QY , UK.
2 Scion , 49 Sala Street, Rotorua 3010 , New Zealand.
J R Soc Interface. 2019 Jun 28;16(155):20190116. doi: 10.1098/rsif.2019.0116. Epub 2019 Jun 5.
The relationship between form and function in trees is the subject of a longstanding debate in forest ecology and provides the basis for theories concerning forest ecosystem structure and metabolism. Trees interact with the wind in a dynamic manner and exhibit natural sway frequencies and damping processes that are important in understanding wind damage. Tree-wind dynamics are related to tree architecture, but this relationship is not well understood. We present a comprehensive view of natural sway frequencies in trees by compiling a dataset of field measurement spanning conifers and broadleaves, tropical and temperate forests. The field data show that a cantilever beam approximation adequately predicts the fundamental frequency of conifers, but not that of broadleaf trees. We also use structurally detailed tree dynamics simulations to test fundamental assumptions underpinning models of natural frequencies in trees. We model the dynamic properties of greater than 1000 trees using a finite-element approach based on accurate three-dimensional model trees derived from terrestrial laser scanning data. We show that (1) residual variation, the variation not explained by the cantilever beam approximation, in fundamental frequencies of broadleaf trees is driven by their architecture; (2) slender trees behave like a simple pendulum, with a single natural frequency dominating their motion, which makes them vulnerable to wind damage and (3) the presence of leaves decreases both the fundamental frequency and the damping ratio. These findings demonstrate the value of new three-dimensional measurements for understanding wind impacts on trees and suggest new directions for improving our understanding of tree dynamics from conifer plantations to natural forests.
树木的形态与功能之间的关系是森林生态学中一个长期存在的争论主题，为有关森林生态系统结构和代谢的理论提供了基础。树木与风以动态的方式相互作用，表现出自然摆动频率和阻尼过程，这对于理解风害很重要。树木与风的相互作用与树木的结构有关，但这种关系尚未得到很好的理解。我们通过编译一个涵盖针叶树和阔叶树、热带和温带森林的野外测量数据集，提供了树木自然摆动频率的综合观点。现场数据表明，悬臂梁近似可以很好地预测针叶树的基频，但不能很好地预测阔叶树的基频。我们还使用结构详细的树木动力学模拟来测试树木自然频率模型的基本假设。我们使用基于地面激光扫描数据的精确三维模型树的有限元方法对 1000 多棵树的动态特性进行建模。我们表明：（1）阔叶树基频的剩余变化（不能用悬臂梁近似解释的变化）是由其结构驱动的；（2）细长的树木表现得像一个简单的摆，只有一个主导其运动的固有频率，这使它们容易受到风害的影响；（3）叶片的存在降低了基频和阻尼比。这些发现证明了新的三维测量对于理解风对树木的影响的价值，并为从针叶树种植园到天然林，提高我们对树木动力学的理解提供了新的方向。
