UC Davis study reveals wildfire smoke cuts nut yields by 50%

Orchard trees in California are at risk from long-term smoke exposure due to massive wildfires, which can reduce nut production by up to 50%, according to a new study from the University of California, Davis.

The research highlighted how wildfire smoke can impact tree health for months after the fires, leading to reduced bloom and harvest in subsequent seasons.

Published in Nature Plants, the study “Megafire smoke exposure jeopardizes tree carbohydrate reserves and yield” analyzed the effects of smoke on almond, pistachio and walnut trees at 467 orchard sites in California’s Central Valley from 2018 to 2022. The findings revealed that smoke can lower trees’ carbohydrate reserves, which are essential for their growth and survival, especially during times of stress.

“A lot of research focuses on the impact of smoke on humans, but there is less study on the effects of smoke on plant health,” said lead author Jessica Orozco, a postdoctoral researcher at UC Davis. “Our study suggests that trees are just as vulnerable as humans.”

The study found that wildfire smoke — particularly from the 2020 fires, which burned over 4.2 million acres in California — reduced the amount of sunlight available for photosynthesis, leading to a significant drop in the trees’ carbohydrate levels. This deficiency affected the trees’ ability to store energy for dormancy and spring growth, contributing to yield losses.

Nut yield declines following wildfires

Growers saw production declines of 15% to 50% due to the lingering effects of smoke, which persisted even after the fires subsided.

“We weren’t expecting the smoke to have such a lingering effect and result in a significant drop in yield,” Orozco noted.

Additional authors on the study included Maciej A. Zwieniecki, professor, and Paula Guzmán-Delgado, postdoctoral researcher, of the UC Davis Department of Plant Sciences.

The Almond Board of California, the California Pistachio Research Board, the California Walnut Board and the California Department of Food and Agriculture supported the research.