California's coast redwoods are iconic anchors of their ecosystem and a draw for millions of tourists, but new research indicates they are vulnerable to extreme heat in ways not previously documented. A study led by UC Davis researchers measured photosynthesis in redwoods in Mendocino County and found that during heat waves, the trees' leaves stop taking in carbon dioxide because they cannot cool down fast enough. That means the trees conserve water but also stop "eating," potentially starving themselves over time.
Because redwoods store more carbon per acre than any other forest in the world, reduced photosynthesis could also weaken their role as a natural climate buffer. According to researchers cited in the WIRED article, less carbon uptake means slower growth and fewer resources to maintain their canopies, which support soil mats, ferns, and animals such as wandering salamanders and marbled murrelets. Even if the trees survive, they may not grow as tall or host as much life as they once did.
The threat is compounded by changing fog patterns. Coast redwoods draw water directly from fog and benefit from its cooling shade, but warmer oceans and drier air are making fog more sporadic. Researchers describe the combination of heat stress and fog loss as a "double whammy." The findings raise urgent questions about the future of these trees and the economic and ecological benefits they provide, though the study is one snapshot of a slow-moving process that will require continued observation.