Heat Waves Reduced Redwood Photosynthesis, Study Found
New research shows California redwoods restrict carbon intake during extreme heat to conserve water.
Updated on Oct. 6, 2026 in Botany
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University of California Davis researchers observed that coast redwoods close their stomata during extreme heat to survive, which halts photosynthesis. This behavioral adjustment during heat stress represents a first-of-its-kind observation for the species.
Why it matters
As coastal fog declines by 30 to 40 percent in Northern California, coast redwoods face increased temperature stress outside their optimal range of 8 to 27 degrees Celsius. This shift threatens the long-term carbon sequestration capacity and growth rates of these forests.
Coast redwoods function within a specific thermal window of 8 to 27 degrees Celsius. When temperatures exceed this range, the trees seal their stomata to prevent excessive water loss, effectively pausing carbon dioxide intake.
The players
University of California Davis
A public research university recognized for its extensive agricultural and environmental science programs.
The details
To regulate gas exchange, redwoods utilize stomata, which are microscopic pores on the surface of leaves that control both water vapor loss and carbon dioxide intake. During extreme heat, the trees undergo a trade-off: they prioritize water conservation through transpiration—the process where plants release water vapor to cool their leaves—over photosynthesis. While researchers confirmed that the trees did not lose the permanent capacity to photosynthesize after heat waves subsided, the reduced carbon intake may lead to diminished tree height.
Timeline
1974: A tree-trimmer located a marbled murrelet nest 150 feet above the ground.
Two-year study period: Researchers monitored leaf photosynthesis in Mendocino County.
In 5 or 10 years: The projected timeframe for increased heat wave frequency and intensity.
The Tech Race
This study provides a new empirical baseline for how coast redwoods respond to climate-driven heat stress. It marks a departure from historical forest monitoring by documenting real-time physiological responses rather than just long-term growth patterns.
The findings suggest that California's forest-based carbon sequestration could decrease as heat waves impact redwood development. Residents in forested areas can monitor future reports on how these climate-induced growth changes influence local ecosystem health.
The takeaway
Redwoods are adapting to extreme heat by sacrificing photosynthesis for water preservation, a move that likely hampers their long-term growth. Observers should track climate models regarding the frequency of heat waves in Mendocino County over the next decade to gauge the cumulative impact on forest size.
Further reading
For more on plant physiology in the state, visit Botany.
Source note: This article includes information reported by Vox.
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