# Heat is breaking redwoods' ancient spell > Coast redwoods shut down photosynthesis in extreme heat, threatening the creatures and ecosystems that depend on them. - Title: Heat is breaking redwoods' ancient spell · Vox | Shortify - Summary: Coast redwoods shut down photosynthesis in extreme heat, threatening the creatures and ecosystems that depend on them. A UC Davis study found coast redwoods… - Keywords: coast redwoods, photosynthesis, climate change, heat stress, uc davis, carbon starvation, forest ecosystems, california, news, culture, Heat, breaking - Source: Vox — https://vox.com/climate/504991/redwood-tree-california-heat-photosynthesis - Author: Neel Dhanesha - Published: 2026-10-06T10:00:00+00:00 - Read time: 3 min - Topics: coast redwoods, photosynthesis, climate change, heat stress, uc davis, carbon starvation, forest ecosystems, california, news, culture ## Redwoods are forests within forests Coast redwood groves host entire ecosystems hundreds of feet above ground. Wandering salamanders spend their whole lives on single trees, and the marbled murrelet nests high in the canopy. ## Trees grow other trees in their branches Stray seeds of sitka spruce, oak, or even other redwoods find their way up massive redwoods and grow into trees nestled among the branches of giants. ## Redwoods anchor stable ecosystems For millennia, redwoods have anchored incredibly stable ecosystems and survived wildfires that devastate other species. They drive millions of dollars to California's tourist economy. ## Heat makes redwoods stop eating A UC Davis study found coast redwood leaves dial down photosynthesis during extreme heat. Trees slow their breathing and eating because they cannot cool down fast enough when temperatures rise. ## How trees breathe and drink Trees use stomata, pores in their leaves, to take in carbon dioxide and let water out. Open stomata mean photosynthesis happens but water escapes. Closed stomata conserve water but stop photosynthesis. ## Leaves heat up like asphalt Leaves are light-absorbing objects that heat up faster than surrounding air. Trees cool themselves by opening stomata and letting water transpire, like humans sweating, but only if they have enough water. > Because leaves are a physical, light-absorbing object, they heat up just like asphalt would in the sun. ## Redwoods studied in Mendocino County Researchers measured coast redwoods in Mendocino County, near the southern part of their range. During heat waves, trees cannot cool down fast enough and keep stomata closed, stopping carbon intake. ## Carbon starvation threatens survival Trees without enough stored carbon cannot replenish leaves efficiently, slowing photosynthesis further and starving them more. This vicious cycle could eventually kill trees, though tropical trees show this behavior first. > The term people use is carbon starvation. Leaves can be expensive to build for a plant. ## New-growth forests are hungrier Most California and Pacific Northwest redwoods are new-growth forests planted in the last couple of centuries. These relatively young trees need to absorb lots of carbon dioxide to grow taller than old-growth cousins. ## Redwoods store more carbon than any forest Redwoods store more carbon dioxide per acre than any other forest in the world. Less carbon sequestration means trees grow smaller, leaving less space for ferns, soil mats, and the creatures living there. ## Fog is disappearing from the coast Coast redwoods sip water directly from fog layers their canopies reach into. Fog also shades trees and helps create cooler microclimates. But warmer oceans and drier air make fog more sporadic. ## Trees face double stress from heat and drought Redwoods live in a narrow temperature range of eight to twenty-seven degrees Celsius, about forty-six to eighty degrees Fahrenheit. Fog, which acts like an air conditioner, has declined between thirty and forty percent. > It's kind of a double whammy. They're running out of water and also getting this heat stress. ## Heat threatens the creatures above Excessive summer heat dries out soil mats and ferns high in redwood canopies. Salamanders and birds may not survive there, causing cascading effects through the entire ecosystem living in the trees. ## Recovery depends on future temperatures Leaves studied over two years did not lose photosynthesis capacity after heat passed, offering some hope. But if temperatures rise further and heat waves become more frequent in five or ten years, recovery may not happen. > Right now the temperatures are coming back to normal in the fall and winter and letting the trees recover. But in five or ten years, if temperatures are even hotter and heat waves are even more frequent, we don't really know if there would be a recovery. ## Key takeaway A UC Davis study found coast redwoods close their leaf pores during heat waves to conserve water, stopping photosynthesis and risking carbon starvation as climate change intensifies.