California’s coast redwoods are some of the tallest living things on Earth, and they have spent millions of years growing in a narrow strip along the state’s foggy shores. Their comfort zone is cool and damp, with average temperatures around 59 degrees Fahrenheit, or about 15 degrees Celsius. But the climate is changing faster than anyone expected, and the trees are now doing something remarkable: they are slowing down their basic functions when the heat spikes.
A new study from the University of California, Davis found that as average yearly temperatures rise and heat waves push past 100 degrees Fahrenheit — about 38 degrees Celsius — the redwoods are responding by slowing their “breathing” and “eating.” The trees are reducing their photosynthesis and slowing their absorption of nitrogen and other essential elements from the soil.
The findings come at a moment when the world’s forests are being watched closely as natural sponges for atmospheric carbon. Redwoods are particularly important because they can live for thousands of years and grow to massive sizes, making them among the best carbon-storing plants on the planet. If they stop growing, the global carbon budget gets smaller.
What the Study Found
The Davis researchers measured how redwoods respond to heat waves by looking at their gas exchange and nutrient uptake. When temperatures climb above the threshold, the trees reduce their photosynthesis, the process by which they convert sunlight into energy. They also slow their absorption of nitrogen and other essential elements from the soil.
The effect is not permanent. Once the heat subsides, the trees recover. But repeated exposure to extreme conditions could push them beyond their recovery capacity, and the study suggests that the warming trend is already testing the limits of these ancient giants.
Coast redwoods are adapted to mild, foggy climates. Their stomata — the tiny pores on leaves that let in carbon dioxide — evolved for air that is humid and cool. When temperatures rise, those pores close slightly to protect the tree from losing too much water through evaporation. That closure slows photosynthesis, and the tree produces less energy.
The slowdown in nutrient uptake is harder to explain directly, but it likely follows the same logic. Heat stress diverts energy away from growth and toward basic survival functions. The tree invests less in roots and leaves and more in protecting itself from damage.
Why This Matters for Carbon Storage
Forests remove carbon dioxide from the air through photosynthesis and store it in wood, leaves, and soil. Scientists call this “carbon sequestration,” and it is one of the few natural processes that can offset human emissions.
Redwoods are especially effective at this. A mature redwood can hold substantial amounts of carbon in its trunk, branches, and roots. A single acre of redwood forest can store significant carbon compared to other land uses. When the trees slow their growth, they store less carbon per year, which reduces their role as a natural carbon sink.
The Davis study does not measure the total carbon impact of the slowdown. It documents the mechanism: the tree slows its breathing and its eating when it gets too hot. The full accounting of how much carbon storage declines would require longer-term measurements of tree growth and biomass.
What the study does establish is a clear link between rising temperatures and reduced metabolic activity in these trees. That link matters for the broader question of how forests will respond to climate change, because redwoods are not the only species showing this pattern.
How Redwoods Are Different From Other Trees
Not all trees respond to heat the same way. Some species are adapted to hotter environments and thrive in warmer conditions. But coast redwoods are not built for heat. Their range hugs the Pacific coast, where fog provides moisture and shade, and they have never faced sustained temperatures above 100 degrees Fahrenheit.
The study focuses specifically on coast redwoods, which grow in the narrow coastal strip from southern Oregon to central California. These trees are distinct from inland redwoods, which grow in the Sierra Nevada mountains and have somewhat different tolerances. The Davis research does not cover inland redwoods, so it is not possible to say whether they show the same response.
What the study does show is that even within one species, there is a thermal ceiling. The redwoods can handle brief heat waves, but prolonged exposure changes their behavior.
The Climate Context
The Davis study comes at a moment when climate data is becoming increasingly alarming. Heat waves are becoming more frequent and more intense globally, and scientists expect this trend to continue as greenhouse gas concentrations rise.
For coast redwoods, the stakes are high. These trees define the landscape of Northern California, and they provide habitat for countless species of plants and animals. A decline in their health could ripple through the entire ecosystem.
The study does not predict how far the trees will slide. It simply documents what happens when the temperature crosses the threshold. That documentation matters because it provides a baseline for future research. If temperatures keep climbing, scientists can return to these trees and measure whether the slowdown accelerates.
What Happens Next
The Davis study is descriptive, not predictive. It tells us what the trees are doing now, not what they will do in 20 years. But the trajectory is clear: as temperatures rise, redwoods breathe and eat less.
The study’s authors have not yet published a detailed analysis of the potential consequences for the forest ecosystem. Such an analysis would require tracking multiple variables over a longer period. The current findings are a snapshot, and snapshots often raise more questions than they answer.
One obvious question is whether the trees can adapt. Evolution takes time, and redwoods have been around for tens of millions of years. They have survived previous warm periods, but the current rate of change is faster than anything they have faced in recorded history.
A Sign of Stress
The Davis study offers a sobering look at how a keystone species responds to a warming world. Coast redwoods are not the only trees showing signs of stress, but they are among the most visible. Their massive trunks and towering heights make them easy to love, and their ecological role makes them essential.
The trees are not dying en masse. They are not falling over or turning brown. But they are changing, and the change is happening at the cellular level. Slower growth means less carbon storage, which means the forest contributes less to the global climate balance.
The study is a reminder that climate change is not abstract. It is not just a distant threat. It is a force that alters the behavior of living things in ways that are difficult to see from the ground but impossible to ignore.
| Comparison | Coast Redwoods Today | Expected Under Continued Warming |
|---|---|---|
| Average Temperature | Around 59°F (15°C) | Rising |
| Heat Wave Threshold | Above 100°F (38°C) | More frequent |
| Photosynthesis Rate | Slows during heat waves | Further reduction possible |
| Nutrient Uptake | Slows during heat waves | Further reduction possible |
| Carbon Sequestration | Reduced per year | Likely declines further |
The comparison shows the direction of travel. The redwoods are already operating outside their historical comfort zone, and the study suggests that the warming trend is pushing them toward a new normal that is less productive.
What We Make of It
The Davis study is a warning, not a verdict. It documents a mechanism — the tree slows its breathing and its eating when it gets too hot — and it connects that mechanism to a broader trend. The trees are stressed, and the stress is measurable.
The study does not say what happens if the warming continues. It does not say the trees will die. It does not say the forest will collapse. But it does say that the trees are changing, and that change has consequences for the carbon cycle.
The redwoods have survived everything nature has thrown at them. Whether they survive this is not yet known. What is known is that they are already changing, and the change is happening now.
The study’s findings are a call to action. The trees are telling us something about the world, and the message is simple: the climate is changing, and the living things in it are responding. The question is whether we will listen.
Source material: “Coast redwoods slow their 'breathing' and 'eating' when temperatures spike,” Phys.org.
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