Monitoring Tree Sway as an Indicator of Interception Dynamics Before, During, and Following a Storm

Understanding the role of trees in attenuating the timing and magnitude of effective precipitation reaching the land surface requires improved monitoring of interception dynamics. We developed a new field monitoring approach to leverage continuous monitoring of tree sway motion in quantifying continuous, dynamic time series of canopy water storage during storms. Using this approach, we additionally observed a hysteretic interception response in tree canopies, which indicates that interpreting interception processes through tree sway signals requires the consideration of changing water (i.e., mass) distribution during and following storms. These findings suggest that continuously monitoring tree sway motions offers a new technique to quantify interception processes. This advancement in whole tree interception may help improve our understanding of how interception affects ecosystem water availability/productivity and runoff dynamics that are important for both natural ecosystems and stormwater management in cities. Plain Language Summary In our work, we are trying to learn about how much water a tree stores in its canopy during storms by tracking changes in tree sway movements. During a storm, we found that the motion of a tree swaying back and forth becomes slower when a tree gets very wet. We also found that a tree's swaying motions became faster as a tree dried out. We also learned that a tree's swaying motions also change depending on where that rainwater is in the canopy. A tree will sway slower if rainwater is closer to the top of the canopy and a tree will sway faster if rainwater is closer to the bottom of the canopy. Overall, this research suggests that if we carefully watch and track changes in the ways a tree sways we can also understand and estimate how much rainwater a tree has captured, and where that rainwater is within the canopy, during a storm. Key Points Monitoring tree sway period provides an aggregated signal of interception dynamics during and following a storm Tree sway monitoring offers a novel, inexpensive approach for quantifying whole canopy interception through time Trees accumulate rainwater and dry from the top down, which causes hysteretic changes in tree sway during wetting and drying cycles

Automated summary

Understanding the role of trees in intercepting and storing rainwater requires improved monitoring techniques. This study found that monitoring tree sway can help quantify interception dynamics, especially during and after storms. The research also revealed that trees accumulate rainwater from top to bottom and experience hysteretic changes in sway during wetting and drying cycles.