New perspectives on the ecology of tree structure and tree communities through terrestrial laser scanning

Abstract

Terrestrial laser scanning (TLS) opens up the possibility of describing the three-dimensional structures of trees in natural environments with unprecedented detail and accuracy. It is already being extensively applied to describe how ecosystem biomass and structure vary between sites, but can also facilitate major advances in developing and testing mechanistic theories of tree form and forest structure, thereby enabling us to understand why trees and forests have the biomass and three-dimensional structure they do. Here we focus on the ecological challenges and benefits of understanding tree form, and highlight some advances related to capturing and describing tree shape that are becoming possible with the advent of TLS. We present examples of ongoing work that applies, or could potentially apply, new TLS measurements to better understand the constraints on optimization of tree form. Theories of resource distribution networks, such as metabolic scaling theory, can be tested and further refined. TLS can also provide new approaches to the scaling of woody surface area and crown area, and thereby better quantify the metabolism of trees. Finally, we demonstrate how we can develop a more mechanistic understanding of the effects of avoidance of wind risk on tree form and maximum size. Over the next few years, TLS promises to deliver both major empirical and conceptual advances in the quantitative understanding of trees and tree-dominated ecosystems, leading to advances in understanding the ecology of why trees and ecosystems look and grow the way they do.

Large‐Scale Geographical Variations and Climatic Controls on Crown Architecture Traits

“…The lack of efficient and accurate methods to obtain repeatable crown architecture observations has long been a bottleneck in the field of crown architecture studies (Malhi et al, ). The rich and accurate three‐dimensional information provided by TLS data has made the estimation of crown architecture traits in a repeatable and accurate manner become possible over large spatial scales in this study.…”

“…For example, it was found that taller trees incline to occur at places with higher water availability (Tao et al, ) and show higher vulnerability to droughts (Bennett et al, ), while at a given latitude of temperate biomes, larger and thinner leaves are easier to be found in a wetter environment (Lusk et al, ; Wright et al, ). However, crown architecture traits, as an essential link between trunk and leaf traits (Savage et al, ), are still much less studied in the fields of ecology and plant physiology (Escudero et al, ; Malhi et al, ). Although there have been theories predicting that in a light‐driven environment, shade‐tolerance trees may develop wider crowns and solider branches, and heliophile trees may have narrower crowns under the canopy and develop larger crowns once reaching open spaces to maximize light capture (Davies & Ashton, ; Sterck et al, ; Wright et al, ), most of these studies are still based on empirical descriptions or model simulations at a local scale (Chave et al, ; Escudero et al, ; Ishii & Asano, ; Malhi et al, ; Pearcy et al, ; Valladares & Pugnaire, ).…”

“…For example, Jackson et al () modeled the motion of tree crowns in the wind from TLS data; Puttonen et al () found that TLS could be used to monitor overnight sleep movements of tree branches and argued that TLS could be used to support chronobiology studies; Magney et al () proved that TLS could be used to investigate canopy light regime and reveal patterns of photosynthetic partitioning; Lau et al () used TLS technique to validate the crown architecture‐based metabolic scaling exponents of tropical trees. It is believed that TLS can lead the advances in understanding how tree architectures are influenced by environmental stresses (Malhi et al, ).…”

“…However, crown architecture traits, as an essential link between trunk and leaf traits (Savage et al, 2010), are still much less studied in the fields of ecology and plant physiology (Escudero et al, 2017;Malhi et al, 2018). Although there have been theories predicting that in a light-driven environment, shade-tolerance trees may develop wider crowns and solider branches, and heliophile trees may have narrower crowns under the canopy and develop larger crowns once reaching open spaces to maximize light capture (Davies & Ashton, 1999;Sterck et al, 2001;Wright et al, 2005), most of these studies are still based on empirical descriptions or model simulations at a local scale (Chave et al, 2005;Escudero et al, 2017;Ishii & Asano, 2010;Malhi et al, 2018;Pearcy et al, 2005;Valladares & Pugnaire, 1999). How crown architecture traits acclimate to the climate variability over large spatial scales and whether there are coordinated relationships among trunk, leaf, and crown architecture traits remain important unknown questions in the field.…”

“…photosynthetic partitioning; Lau et al (2019) used TLS technique to validate the crown architecture-based metabolic scaling exponents of tropical trees. It is believed that TLS can lead the advances in understanding how tree architectures are influenced by environmental stresses (Malhi et al, 2018).…”