Accelerometers Track Urban Tree Phenology.

• Position: ARBORISM

Low-cost "tree titbits" can pinpoint the precise timing of tree activities, like spring bloom or autumn leaf change, according to a University of Colorado study. Researchers outfitted two East Boulder ash trees with high-resolution accelerometers, efficiently tracking how the trees responded to changing seasons-and, in the coming years, arborists efficiently could monitor trees by the thousands with this technology--ultimately giving researchers insight into how tree phenology is changing with a warming climate.

"Accelerometers are in cars, smartphones, and fitbits--they track movement in real time. When we put them on trees, accelerometers detect vibrations on the trunk as the tree sways in the wind," says Deidre Jaeger of the Cooperative Institute for Research in Environmental Sciences and lead author of the study published in Agricultural and Forest Meteorology. "That sway corresponds to the tree's mass, which tells us what the tree is doing."

A tree's mass all depends on its water uptake throughout the seasons, creating the structural differences that determine how it dances in the wind. In the winter, trees are dry and brittle. 'Think of the quick, shaky rattling sound of leafless trees in the dead of winter," Jaeger says. "Now think of spring: the trees are lush with leaves, full of water, and sway with flexibility."

A previous accelerometer study was able to detect when trees' leaf buds opened or when leaves dried and fell off, but Jaeger's team proved how much more detailed data such tree titbits can collect. The team picked up the precise moment when white ash trees flowered, catching the subtle change in movement that corresponded to the trees blossoming and pollen release.

Jaeger and her team outfitted two white ash trees on the east campus in 2018, working with arborist Vince Aquino to strap equipment...