Wildfires can destroy large tracts of vegetation. But their smoke plumes may help crops and other plants use sunlight more efficiently.

In summer 2018, severe wildfires ravaged California. Fires broke out across the state beginning in July, including California’s largest wildfire on record. The fires’ impacts reached well beyond their devastating footprints as millions of people across the country inhaled particulate matter from the smoke.

Huge plumes of smoke also drifted through California’s typically sunny Central Valley during peak growing season in 2018, blanketing several kinds of crops and ecosystems. In new research, Hemes et al. turned their attention to the ecological effects of the smoke-smudged sky, studying how wildfire-induced haze in the air affects photosynthesis and productivity in different restored and cultivated ecosystems.

The researchers’ measurements showed that the total amount of sunlight available to plants for photosynthesis decreased only slightly—by about 4%—compared to the previous summer. In other words, the smoke didn’t block the light; it scattered it, increasing the amount of diffuse light by about a third. Whereas direct sunlight might fall mainly on upper foliage, leaving the rest of a plant in shade, diffuse light can reach a greater number of photosynthesizing leaves throughout the vegetation canopy. Because of the haze, plants used the available light nearly twice as efficiently, the team reported.

Wildfires contribute to the production of ozone, which negatively affects plant growth, but in this case, the benefits of diffuse light outweighed any detriment from ozone. The researchers also found that crops benefited more than the restored wetland ecosystems they studied, and the diffuse light increased photosynthetic efficiency more for plants with taller canopies, like corn, or those with a lot of leaf area, like mature alfalfa.

As climate change makes parts of the world warmer and drier, these results will help researchers understand how more frequent and longer-lasting wildfires affect downwind ecosystems and agriculture. Similar studies have also considered the positive and negative ramifications for ecosystems of injecting aerosols into the air to counter effects of climate change or of highly polluting cities in developing countries. Finally, further studies could use crop production and harvest as a measure of productivity as scientists continue to parse the nuances of wildfires and their effects on cultivated and wild plants. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2019JG005380, 2020)

—Elizabeth Thompson, Science Writer