The complexity of tree architecture may be the reason we find trees relaxing but it is hard to account for in ecology.
Along with our colleagues from UCL and Wageningen University, we mapped the range of tree architecture using terrestrial laser scanning data. This was done by scanning trees and forests from multiple locations, fitting cylinders to the raw point cloud data and then extracting architectural metrics from those cylinder models. Overall, the results were pretty intuitive: trees from tropical forests span a wider range of architectures than those from temperate forests or open-grown, tree size was the primary axis of variation and the second axis was driven by crown shape
More interestingly, open-grown trees tended to cluster around high path fraction, which can be interpreted as a measure of hydraulic efficiency. Path fraction is defined as the ratio of the mean to maximum trunk-to-twig path length. Ideal fractal trees, the most hydraulically efficient architecture, will have a path fraction of 1, while real trees will always be below 1. The hydraulically efficient architecture evident in the open-grown trees may be due to the absence of competition for light, allowing them to grow into a more optimal shape.
This analysis was part of a recent article exploring the natural sway frequencies of trees. We found that, while conifers behave like simple beams, broadleaf tree architecture plays an important role in determining their response to wind loading.
If you’d like to see more 3D models of trees check out this and this. If you are interested in extracting tree architectural indices from terrestrial laser scanning data have a look at the TreeQSM and treestruct github pages.