Smoke from wildfires poses serious threat to agriculture: Study

Long-term exposure to wildfire smoke can significantly reduce orchard trees’ energy reserves and cut nut production by 50%, according to a University of California, Davis study. The research highlights a previously underexplored consequence of wildfires that could impact agriculture and plant health.

Wildfire smoke reduces tree energy

The October 2 Nature Plants study focuses on the lasting effects of wildfire smoke on almond, pistachio, and walnut trees in California’s Central Valley, a major U.S. nut production hub. Researchers found the smoke can affect the trees for months after a wildfire, reducing their bloom and significantly lowering the harvest in the following season.

Jessica Orozco, the study's lead author and a postdoctoral researcher at UC Davis's Department of Plant Sciences, emphasized the research's importance. "A lot of attention is given to wildfire smoke's impact on human health, but little is known about its effect on plants," Orozco said. "Our findings suggest trees are as vulnerable as humans to smoke exposure."

Between 2018 and 2022, scientists studied orchard trees at 467 sites across California's Central Valley. The research included the 2020 wildfire season, which saw over 4.2 million acres burn, filling the skies with smoke and ash. While the team aimed to study how trees store energy as carbohydrates to cope with heat and drought stress, the wildfires provided a unique opportunity to assess the impact of smoke on tree health.

Carbohydrates are critical for tree survival, storing energy from photosynthesis. Trees use this energy for growth and to survive stressful conditions, including reduced or stopped photosynthesis during smoke-filled skies.

Thick smoke blocks tree sunlight

Wildfire smoke blocks sunlight, which trees need for photosynthesis. While smoke particles can scatter sunlight and create more diffused light to enhance carbohydrate production, Orozco’s study found that during megafires, the smoke is often so thick that it blocks too much direct sunlight for trees to compensate.

This disruption in photosynthesis depletes the trees' energy reserves, reducing their ability to store carbohydrates. The long-lasting effect continues after the fires are extinguished, impacting the trees' ability to bloom and produce nuts for the next season's harvest.

The research revealed orchards saw a 15% to 50% reduction in nut yield after exposure to wildfire smoke. This decline is concerning because wildfires often overlap with a critical period when trees store carbohydrates to survive winter dormancy and support spring growth.

Orozco said, "We anticipated some negative effects during the months of dense smoke, but we were surprised by the lasting impact on tree health and the significant decline in yield."

Smoke reduces tree energy reserves

The study shows smoke impacts trees, but the exact components of wildfire smoke causing the carbohydrate reduction remain unclear. During the 2020 fires, smoke reduced sunlight and increased ozone and particulate matter levels, affecting photosynthesis. Researchers believe one or a combination of these factors could be responsible for the decrease in tree energy reserves.

Orozco emphasized that more research is needed to identify the smoke elements that harm plant health.

The study highlights the growing threat of climate change and increased wildfire activity to agriculture, particularly in California, where wildfires are becoming more frequent and severe. Long-term smoke exposure could impact crop yields, affecting food supply and prices.

The findings have implications beyond orchards. Wildfire smoke may affect trees and plants in natural ecosystems, disrupting habitats and food chains. "We need to consider wildfire smoke as an environmental hazard not just for humans, but for the entire ecosystem," Orozco said.

Professor Maciej A. Zwieniecki and postdoctoral researcher Paula Guzmán-Delgado from UC Davis co-authored a study that calls for more investigation into the long-term effects of wildfire smoke on plant health. Identifying the most harmful smoke components could help develop strategies to mitigate the impact on agriculture and the environment.

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