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# Coast-redwood leaves crossed a photosynthetic heat threshold before air temperature told the whole story
- URL: https://intelligence.wildlandseco.com/2026-10-02-redwood-heat-photochemistry-threshold/
- Published: 2026-10-02T13:48:40.000Z
- Updated: 2026-10-02T13:48:40.000Z
- Description: Two years of leaf physiology in Mendocino County found redwood leaves could run up to 10°C warmer than air, with photosynthesis declining above about 30°C and more steeply above 35°C.
- Author: Benjamin Worlund
- Tags: coast redwood, heat stress, photosynthesis, leaf temperature, forest resilience, Land, Climate, Forestry, Physiology, #ecological-intelligence, #brief-2026-10-02, #global-radar, #peer-reviewed, #geo-north-america

Evidence

Peer-reviewed

Geography

Garcia River Forest, Mendocino County, California, USA

System

Coast redwood forest

## WHAT THE EVIDENCE SAYS

Repeated lower-canopy measurements from three young coast redwoods over two years showed leaf temperatures frequently exceeded air temperature during summer stress, with leaf-to-air differences reaching 10°C. Photosynthetic efficiency fell as leaves warmed, and controlled temperature-response curves showed net photosynthesis declining above about 30°C with steeper losses above 35°C. Internal CO₂ remained high during much of the decline, supporting a non-stomatal biochemical limitation rather than stomatal closure alone.

## WHY IT MATTERS / OUR READ

Air temperature is an incomplete exposure metric when leaves can decouple from it. For redwood monitoring, leaf thermal status and water stress may reveal physiological limits that a weather station alone misses.

## CAVEATS / UNCERTAINTY

The field physiology comes from three young trees, lower-canopy branches and one second-growth forest; temperature-response curves used detached, well-watered branches. Leaf-level responses do not directly quantify whole-tree growth, mortality or stand-level carbon sequestration.

## SOURCE

JGR: Biogeosciences — primary study  
[View original evidence ↗](https://doi.org/10.1029/2026JG010052?ref=intelligence.wildlandseco.com)

From the Morning Brief · 2026-10-02

[Read the full Morning Brief →](https://intelligence.wildlandseco.com/morning-brief-2026-10-02/)