Exposure to smoke from megafires can significantly impact the yield of almond, walnut, and pistachio trees. Recent research indicates that the effects of smoke can diminish a tree’s energy stores long after the fire has been extinguished.
A study conducted by researchers at the University of California, Davis, reveals that prolonged exposure to smoke from large forest fires can severely reduce the energy reserves of orchard trees, potentially halving their nut production. The smoke can have lasting effects on trees for several months following a megafire, negatively impacting their flowering and subsequent harvests. This discovery highlights a previously unrecognized threat from wildfires, which may jeopardize plant health in both agricultural and natural settings.
Nature Plants has published this study as of October 2nd.
Lead author Jessica Orozco, a postdoctoral researcher in the UC Davis Department of Plant Sciences, remarked, “Much of the research has primarily focused on the effects of smoke on humans, with less emphasis on how smoke impacts plant health. Our findings indicate that trees are equally susceptible.”
Dim skies lead to reduced energy for trees
Over a period from 2018 to 2022, scientists examined almond, pistachio, and walnut trees across 467 orchard locations in California’s Central Valley. In 2020, widespread megafires burned more than 4.2 million acres in California, releasing substantial amounts of smoke and ash into the atmosphere. At that time, researchers were investigating how trees accumulate energy in the form of carbohydrates to withstand heat and drought, but they recognized an opportunity to explore the impact of smoke on these energy stores.
“Carbohydrates produced through photosynthesis are vital for a tree’s survival,” Orozco explained. “Trees rely on carbohydrates not just for growth but also for energy storage during stressful periods or when photosynthesis is not feasible.”
The process of photosynthesis is altered under smoky conditions. Smoke particles hinder some sunlight while reflecting light, resulting in diffused light. This diffused light could aid trees in generating more carbohydrates, but Orozco emphasized that the study showed that the extremely thick smoke likely hindered the benefits of reduced light exposure.
Enduring effects, reduced yields
The researchers discovered that megafire smoke decreased carbohydrate levels in trees, with negative effects persisting post-fire. Consequently, nut yields dropped by 15% to as much as 50% in certain orchards. The peak wildfire season coincides with the period when trees begin to store carbohydrates for the winter dormancy and spring growth phases.
Orozco stated, “While we anticipated some impact, especially during periods of dense smoke, we were surprised by the lasting effects and significant yield reductions.”
The research team is still in the dark regarding which specific components of megafire smoke contributed to the decline in carbohydrate levels in the trees. During the megafires of 2020, smoke not only reduced light levels but also raised ozone and particulate matter concentrations, all of which negatively influence photosynthesis. It remains unclear whether any single factor or a combination of them resulted in the decrease of carbohydrates in the trees.
Other contributors to the study include Professor Maciej A. Zwieniecki and postdoctoral researcher Paula Guzmán-Delgado from the UC Davis Department of Plant Sciences.
This research was supported by the Almond Board of California, California Pistachio Research Board, California Walnut Board, and the California Department of Food and Agriculture.
