Abstract
Urban forests are part of the global forest network, providing important benefits to human societies. Advances in remote-sensing technology can create detailed 3D images of trees, giving novel insights into tree structure and function. We used terrestrial laser scanning and quantitative structural models to provide comprehensive characterizations of the woody surface area allometry of urban trees and relate them to urban tree anatomy, physiology, and structural complexity. Fifty-six trees of three species (Gleditsia triacanthos L., Quercus macrocarpa Michx., Metasequoia glyptostroboides Hu & W.C. Cheng) were sampled on the Michigan State University campus. Variations in surface area allocation to non-photosynthesizing components (main stem, branches) are related to the fractal dimension of tree architecture, in terms of structural complexity (box-dimension metric) and the distribution of “path” lengths from the tree base to every branch tip. The total woody surface area increased with the box-dimension metric, but it was most strongly correlated with the 25th percentile of path lengths. These urban trees mainly allocated the woody surface area to branches, which changed with branch order, branch-base diameter, and branch-base height. The branch-to-stem area ratio differed among species and increased with the box-dimension metric. Finally, the woody surface area increased with the crown surface area of the study trees across all species combined and within each species. The results of this study provide novel data and new insights into the surface area properties of urban tree species and the links with structural complexity and constraints on tree morphology.
Highlights
analysis of variance (ANOVA) showed that the mean BMS differed significantly among the three species, i.e., M. glyptostroboides (MEGL), G. triacanthos (GLTR), and Q. macrocarpa (QUMA) (p < 0.001)
We demonstrated the use of terrestrial laser scanning (TLS) technology to produce detailed data that quantify the total above-ground WSA of urban trees and we found that the study trees varied widely in their WSA
Based on TLS data we studied the allocation patterns of WSA to different components of the woody skeleton of trees, i.e., stem and branches of different order, base-diameter, and base-height classes, and we found that the urban trees allocated their WSA mainly to branches, while branch order, branch-base diameter, and branch-base height influenced the observed allocation pattern
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The fundamental physiological processes of trees, including urban ones, include rates of respiration and photosynthesis, production efficiency, water balance, energy and gaseous exchange with the atmosphere, and leaching of nutrients from bark and leaves [11,12]; all of these have long been hypothesized to relate to tree surface area [13]. The roles of leaf area and crown surface area in tree carbon balance, through photosynthesis and respiration, is well known, e.g., [11,12,14,15,16] and tree respiration rates, in particular, are closely related to their woody surface area [17,18,19,20,21].
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