Long-term exposure to smoke from wildfires can significantly reduce the energy reserves of orchard trees and slash nut production by up to 50%, according to researchers at the University of California, Davis. The study, published on October 2 in Nature Plants, highlights a new risk for agriculture from wildfires.
Lead author Jessica Orozco, a postdoctoral researcher in the UC Davis Department of Plant Sciences, explained that while much research has focused on the effects of smoke on humans, plants are also vulnerable. “Our study suggests that trees are just as vulnerable as humans,” Orozco said.
Researchers studied almond, pistachio, and walnut trees in California’s Central Valley from 2018 to 2022, a period that included the 2020 megafires. These fires burned over 4.2 million acres and filled the air with dense smoke and ash.
Wildfire smoke blocks sunlight, which reduces photosynthesis—trees’ ability to produce carbohydrates that are essential for energy storage and survival. The team found that while diffused light from smoke can sometimes help photosynthesis, the smoke was too thick to make up for the loss of direct sunlight. As a result, carbohydrate levels in trees dropped, leading to a reduction in nut yields.
The lingering effects of smoke persisted even after the fires, leading to harvest reductions of 15% to 50% in some orchards. Orozco noted that further research is needed to understand which components of wildfire smoke are responsible for this decline.
The study was supported by various industry groups, including the Almond Board of California and the California Pistachio Research Board.
Sabrina Halvorson
National Correspondent / AgNet Media, Inc.
Sabrina Halvorson is an award-winning journalist, broadcaster, and public speaker who specializes in agriculture. She primarily reports on legislative issues and hosts The AgNet News Hour and The AgNet Weekly podcast. Sabrina is a native of California’s agriculture-rich Central Valley.