City Trees is a premier publication focused on urban + community forestry. In each issue, you’ll learn how to best manage the trees in your community and more!
Issue link: https://read.dmtmag.com/i/1537178
A Novel, Data-Driven Solution: TLS and Quantitative Structure Modeling The study focused on 24 open-grown honey locust (Gleditsia triacanthos) trees on the Michigan State University campus. The researchers used Terrestrial Laser Scanning (TLS) to create high-resolution, three-dimensional models of each tree. This technology emits millions of laser pulses that reflect off the tree surface, generating a "point cloud" that captures the size, shape, and structure of the entire above-ground portion of the tree—including small and large branches. To connect the TLS-based models to internal wood compo- sition, the team harvested a subset of trees and collected wood disks from both stems and branches. These disks were scanned and analyzed to determine the proportion of heartwood and sapwood using image analysis, with clear color differences allowing precise measurements. Based on these data, statistical models were developed to predict heartwood content from easily observable variables—pri- marily the height of a disk on the stem and the diameter of a branch. These predictive models were then applied to the TLS-derived volume data, allowing researchers to esti- mate total heartwood and sapwood volume for each tree. Several notable patterns emerged from the analysis: • Heartwood dominates the main stem, particu- larly near the base. As one moves up the tree, the heartwood volume steadily declines while sapwood becomes more prominent—consistent with what is expected based on tree physiology. • Branches, especially smaller and upper ones, are primarily sapwood, as these areas are actively conducting water and supporting foliage. However, in larger and lower branches— especially structural forks—heartwood can be substantial. • On average, branch wood volume exceeded stem wood volume, with branches containing up to 2.3 times more wood than the stem in some trees. This highlights the importance of including branches in any comprehen- sive assessment of urban tree biomass and structure. • The woody surface area (WSA) of the trees was strongly correlated with sapwood volume. Since WSA is a key factor in determining growth respiration, and sapwood volume relates to maintenance respiration, this relationship pro- vides insight into the balance of energy use within trees. Practical Implications for Urban Forestry The method developed in this study offers a reliable, and scalable way to estimate heartwood and sapwood volumes in living trees, using equipment and modeling tech- niques that are increasingly accessible to researchers and advanced forestry practi- tioners. Future research should combine increment cores and TLS to non-destruc- tively measure sapwood and heartwood. For urban foresters and arborists, this approach opens up new possibilities for: • Assessing tree health: Since sapwood is directly tied to water transport and vitality, its volume and distribution offer clues about a tree's physiological status, while heartwood distribution helps identify areas of structural weakness or decay risk. • Planning maintenance and pruning: Quantifying how wood is distributed can inform decisions about where and how to reduce crown weight safely. • Estimating carbon storage and biomass: For cities tracking carbon offset goals, more precise data on wood volume significantly improves estimates. • Urban wood utilization: When trees must be removed, knowing the pro- portion of heartwood versus sapwood helps inform potential uses for the wood, from lumber to bioenergy. Read the Full academic paper ucfsociety.org 23