Redwood Photosynthesis Declined During Heat Waves

A 2026 study linked rising temperatures to a sharp decrease in carbon intake for California's coast redwoods.

Updated on Oct. 12, 2026 in Botany

Redwood Photosynthesis Declined During Heat Waves

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Research published on September 22, 2026, revealed that photosynthesis rates in coast redwoods drop by half as temperatures climb from 30 to 40 degrees Celsius. Scientists observed this physiological stress in younger trees located within Mendocino County.

Why it matters

When coast redwoods experience intense heat and dry conditions, their stomata close to prevent moisture loss, effectively blocking the carbon dioxide intake needed for photosynthesis. This reaction limits the trees' growth potential as extreme heat events become more frequent.

Needle samples collected from the lower canopy revealed that during extreme heat, needle temperatures can climb up to 10 degrees Celsius higher than the surrounding ambient air. Researchers analyzed these samples under controlled laboratory conditions to track performance fluctuations.

The details

By measuring needle samples gathered from the lower canopy, researchers determined that younger coast redwoods are highly sensitive to thermal stress. The study utilized samples collected 5 meters high to simulate environmental stressors that inhibit gas exchange.

Between July 2022 and October 2024, researchers collected redwood needle samples in Mendocino County.
The research findings were officially published in a journal on September 22, 2026.

The Big Picture

This discovery alters the scientific understanding of forest resilience by highlighting the vulnerability of younger trees to extreme thermal stress. It challenges previous assumptions about redwood hardiness, suggesting that future research must account for leaf-level temperature spikes that occur independently of ambient air temperature.

The findings indicate that younger redwoods may struggle to maintain growth levels during prolonged heat waves, which could alter the composition of California's coastal forests over time. Understanding these physiological limits helps scientists predict how different forest sections will survive shifting climatic patterns.

The takeaway

Coast redwoods employ a survival strategy of closing stomata during extreme heat to retain vital moisture. While this protects the tree in the short term, it creates a trade-off that significantly curtails the energy production necessary for long-term health.