We have all seen trees swaying in the wind, but did you know that tree motion can teach us about ecology? Researchers have monitored tree motion for different purposes, from assessing wind damage risk to monitoring drought stress. Our new paper brings all this data together to study the differences between types of trees and test whether previous results generalize across a range of data sets.
We computed a set of descriptive features from the tree motion time-series data and found that the conifers clustered into a relatively tight group. This shows that trees in conifer forests move in similar ways in response to wind, presumably due to their relatively simple shapes. Conversely, there was a wide variation in the motion of open-grown trees and broadleaf trees. Data availability followed the opposite pattern, with most of the high quality (long-term, well calibrated) data collected in conifer forests. Long-term tree motion data for open grown trees and broadleaf trees were particularly rare, so future research should fill this data gap to help us understand their risk of wind damage.
Measuring the motion of a 65 m tall Coastal Redwood tree in the wind. Photo by Anthony Ambrose.
Previous studies have suggested that additional damping or amplification mechanisms become important at high wind speeds. If true, this would be a key factor in modelling wind damage, which is a driver of forest disturbance (the largest in Europe). We calculated the slope of the power spectrum for each hour of tree motion data and found that it plateaued between medium and high wind speeds. This suggests that no substantial changes in tree motion characteristics occurs across this range. Unfortunately (from a scientific point of view) none of the data sets in this study captured high enough wind speeds to cause tree damage, so we cannot rule out additional effects at higher wind speeds. However, we found no evidence for these effects in the available data.
As you can see from the large author list, this was a collaborative project involving many researchers who made their data openly available and contributed to discussions about the science. All the data we collated for this project are freely available online https://zenodo.org/record/4915883#.YO6phOhKhnJ and we encourage others to download and use it.