The way trees sway may communicate water stress

Water stress in trees, as evidenced by their sway, could offer a new way to monitor drought conditions across the Western U.S. Joe Ammatelli, an assistant research scientist, is developing a method that utilizes existing traffic camera networks to analyze tree sway frequency and potentially detect water stress. This innovative approach could help assess wildfire risk and power line disruptions.

The researchers are studying how water availability affects tree movement and stability, with the goal of using video-processing algorithms to remotely evaluate water stress. The Harvard Forest Climate Interactions with Forest Fragmentation (CLIFF) site in Massachusetts serves as an ideal experimental site, equipped with a system to control water availability and natural stands for comparison.

As trees sway in the wind, their trunk angles shift, creating periodic motion, which can be measured using contact sensors and sap flow sensors. Dendrometers also track tree growth and water loss. The researchers' hypothesis is that drier trees sway at slower frequencies, and by measuring sway frequency over time, they can identify water stress.

Ammatelli's algorithms have shown promise for tall, slender trees but face challenges with trees that have many limbs. The method could potentially be used to identify trees at risk of falling and sparking wildfires, as well as to monitor urban trees for heat stress. The researchers plan to validate their findings using tilt, sap-flow, growth, precipitation, and soil-moisture data, and aim to commercialize the method with support from the Governor's Office of Economic Development.