Heat stress cuts coast redwood photosynthesis, threatens carbon storage in California forests
aol.comA new study from UC Davis shows that coast redwood leaves lose photosynthetic efficiency when they get too hot, even when water and CO2 are available. During heatwaves in 2022 and 2024, leaves in Mendocino County ran up to 10°C warmer than air, and photosynthetic performance dropped sharply. Lab tests confirmed the decline is tied to heat affecting leaf machinery, not just closed stomata. This matters because redwoods store huge amounts of carbon, and slower photosynthesis could weaken their role as a natural carbon sink as heatwaves become more common. Researchers measured 1,527 leaves on three young trees and found that even a 2°C leaf-to-air temperature difference can halve Photosystem II efficiency. The study doesn't yet pin down permanent damage thresholds, but it makes clear that extra water alone won't protect redwoods from extreme heat. That has implications for forest management and carbon accounting in California, where redwood ecosystems are a major carbon reserve. Understanding these limits will be key to predicting how these forests will fare under a warming climate.