Megafire Smoke Endangers Orchard Trees, Reducing Nut Yields

Researchers at the University of California, Davis, discovered that prolonged smoke exposure from large wildfires depletes orchard trees’ energy reserves and can slash nut production by 50%. The smoke impacts trees for months following a megafire, reducing their bloom and next season’s yield. This highlights a new wildfire-related threat to plant health in both agricultural and natural ecosystems.

The study was published in Nature Plants on October 2.

Smoke’s Overlooked Impact on Plant Health

“While much research examines the effects of smoke on humans, there has been less focus on its impact on plant health,” said lead author Jessica Orozco, a postdoctoral researcher at UC Davis Department of Plant Sciences. “Our findings indicate that trees are just as susceptible as humans.”

From 2018 to 2022, scientists studied almond, pistachio, and walnut trees at 467 orchard sites across California’s Central Valley.

In 2020, megafires burned over 4.2 million acres in California, filling the skies with smoke and ash. During that time, researchers were investigating how trees store energy, in the form of carbohydrates, to cope with heat and drought. Orozco explained that this presented an opportunity to examine how smoke influences carbohydrate levels.

“Photosynthesis generates carbohydrates, which are vital for tree survival,” said Orozco. “Trees need carbohydrates not only for growth but also to store energy for times of stress or when photosynthesis is reduced.”

How Smoke Disrupts Photosynthesis

Smoke alters photosynthesis by blocking some sunlight and reflecting it, which creates more diffused light. While diffused light can help trees produce more carbohydrates, the study found that the smoke was so thick it likely didn’t make up for the loss of direct light.

The team discovered that megafire smoke not only reduced trees’ carbohydrate levels but also caused continued losses even after the fires had ended. This led to nut yield reductions ranging from 15% to as much as 50% in some orchards. The peak wildfire season also overlaps with the period when trees begin storing carbohydrates to sustain them through winter dormancy and spring growth.

“We expected some impact, especially during the months of dense smoke, but we didn’t anticipate such a prolonged effect leading to a significant drop in yield,” said Orozco.

Researchers are still unsure which elements of megafire smoke caused the decrease in tree carbohydrates. During the 2020 fires, smoke reduced light and increased ozone and particulate matter levels, all of which influence photosynthesis. Any one or a combination of these factors may have contributed to the carbohydrate decline.

Read the original article on: Phys Org

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