Key message

Spruce trunk tapering corresponds closely to tapering required to resist bending forces caused by wind and gravity.

Abstract

Understanding why trunks (tree stems) are the size that they are is important. However, this understanding is fragmented into isolated schools of thought and has been far from complete. Realistic calculations on minimum trunk diameters needed to resist bending moments caused by wind and gravity would be a significant step forward. However, advancements using this biomechanical approach have been delayed by difficulties in modelling bending of trunks and wind gusts. We felled and measured five Norway spruces (Picea abies) in an unthinned monoculture in southeastern Finland planted 67 years earlier. We then focused on forces working on storm-bent (maximally bent) trees caused by gravity and the strongest gust in a 1-h simulation with a large-eddy simulation model. The weakest points along the trunks of the three largest trees resisted mean above-canopy wind speeds ranging from 10.2 to 12.7 m s⁻¹ (3.3-fold in the strongest gust), but the two smallest were well protected by a dense layer of leaves from the bending tops of larger trees, and could have resisted stronger winds. Gravity caused approximately one quarter of the critical bending moments. The wind that breaks the trunks in their weakest points is close to breaking them in other points, supporting the importance of bending moments caused by wind and gravity in the evolution of trunk taper.

中文翻译：

---

风和重力作用塑造云杉皮树干

关键信息

云杉树干逐渐变细与抵抗风和重力引起的弯曲力所需的逐渐变细。

抽象的

了解树干（树的茎）为何如此重要的大小很重要。但是，这种理解被分散为孤立的思想流派，并且距离完成还很遥远。抵抗风和重力引起的弯矩所需的最小躯干直径的现实计算将是向前迈出的重要一步。然而，由于难以模拟树干弯曲和阵风，使用这种生物力学方法的进展已被延迟。我们砍伐并测量了五种挪威云杉（云杉云杉））是在芬兰东南部67年前种植的未稀疏的单一栽培种中。然后，我们在大涡流模拟模型的1小时模拟中，重点研究了重力和最强阵风引起的在弯曲弯曲（最大弯曲）的树木上作用的力。沿三棵大树的树干的最弱点抵抗的平均冠层风速范围为10.2至12.7 m s ^-1（最强阵风的3.3倍），但最小的两个阵风则受到较大树木弯曲顶部的密密麻麻的叶子保护，可以抵御更强的风。重力造成了临界弯矩的大约四分之一。在树干的最薄弱点折断的风接近在其他点折断风，这支持了风和重力引起的弯矩在树干锥度演变中的重要性。