The world’s oldest trees, California redwoods, are feeling the heat. And warming temperatures are hindering their ability to perform essential functions.
In the hot seat
Redwood leaves “exhibit significant decreases in photosynthesis and carbon uptake” at higher temperatures, said a study published in the journal JGR Biogeosciences. Leaves contain pores called stomata, which take carbon dioxide in and let water out. When open, the tree is “breathing” and photosynthesizing. When closed, the tree is conserving water but not photosynthesizing. In heat, stomata tend to open to release water, essentially sweating.
However, during heat waves, “coast redwoods hit a point where they can’t cool down fast enough, and they just keep their stomata closed,” said Vox. It saves water, but it also means the “tree isn’t taking in more carbon,” therefore not “‘eating’ or building up energy stores it can use to keep growing.” These trees are accustomed to temperatures of 59 degrees Fahrenheit, but when temperatures topped 86 degrees, the “temperatures of some leaves were nearly 20 degrees higher than the temperature of the air,” said a release about the study from the University of California, Davis.
Getting warmer
Slowed photosynthesis could have a “big impact” on redwood forests, “creating a vicious cycle where trees don’t have enough carbon stored to replenish their leaves in the future,” which will “starve them even further.” said Vox. There could be larger environmental implications to this, as redwood forests “store more carbon dioxide per acre than any other forest in the world.”
Heat waves “also burn off the coastal fog that redwoods depend on for much of their water,” exacerbating the stress further, said the release. “We don’t know what the upper temperature thresholds are for redwood photosynthesis and mortality,” study lead author Lily Klinek, a Ph.D. candidate at UC Davis, said in the release. This research is an “important start” for figuring out “what parts of the redwood range are at risk, knowing what to expect and trying to intervene for the health of redwood ecosystems.”