提供荫凉的树木——针对缓和城市局地气候的树木形态类型学描述框架

Cool Tree Architecture:A Descriptive Framework for a Tree Architecture Typology to Temper Urban Microclimates

作为城市森林的基本单元,树木可通过遮荫和蒸腾,以及改变空气流动等途径来调节城市局地气候中的极端高温。然而,目前用来衡量不同树种遮荫效果的指标还很有限,因此需要开发一种新的方法来填补。本文提出了一种通过对影响太阳辐射反射率、吸收率和透射率等树木物理特性进行结构化描述来筛选树种的方法。这一描述性框架基于“树木结构”概念——树木结构已发展成为植物研究领域中一个专门研究植物的外观、形态和发育过程的方向。该框架包含了树冠、枝干和树叶三大总体特征中的多个子形态特征,可用于探究“可提供荫凉的树木形态类型学”(Cool Tree Architecture Typology,C-TAT),并将具有共同物理特征的树种进行分类。通过树木的野外对照实验观察,进一步细化了子形态特征,形成了新的描述指标,成为了C-TAT分类的关键。C-TAT适用于大西洋气候带等地区的城市中的树种形态类型划分,可对现有树木进行更快速的评估和降温绩效计算,并有助于树木管理者对城市开发项目中的树木制定更准确的热性能标准。本文也从城市局地气候的角度丰富了树木结构的研究内涵与方法。

As the elementary unit of the urban forest,trees temper thermal extremes in urban microclimates through shading and evapotranspiration,and by altering the movement of air.Metrics on shade performances of different species,however,are currently limited,which can be remedied by the development of a method to describe the range of species and cultivars via a structured overview of physical characteristics impacting radiation reflectivity,absorptivity,and transmissivity.This paper proposes a descriptive framework based on the concept of“tree architecture,”which has developed into a recognized field of plant study from the perspective of their physiognomy,morphology,and morphogenesis.The framework describes various architectural sub-traits within the overall trait categories of Crown,Wood,and Foliage.The descriptive framework can be used to develop a“Cool Tree Architecture Typology”(C-TAT),in which trees can be organized into similar types based on common physical characteristics.Further elaboration of sub-traits using observations of trees in controlled field laboratories resulted in new derivative classes for use as key in classifications for the C-TAT.The C-TAT can be used to organize the many species and cultivars occurring in,for example,Cfb Atlantic climate zone cities,to a lesser number of architectural types.This allows for more rapid evaluation and cooling performance calculations of tree inventories and can also be of value in assisting tree managers to propose more accurate thermal performance standards for trees in urban projects.The elaboration of tree architecture from an urban microclimate perspective complements existing elaborations and approaches in the field of tree architecture.