New research from UC Davis shows that coast redwoods significantly reduce photosynthesis when temperatures exceed 86 degrees Fahrenheit. The study, published in JGR Biogeosciences, measured leaf temperatures and lab responses over three summers in Mendocino County. Leaves ran nearly 20 degrees hotter than the air, indicating the trees were closing stomata to conserve water, even when water was available. The findings raise concerns about the resilience of redwood forests as heatwaves become more frequent. If these iconic trees cannot cool themselves effectively, their carbon uptake and growth will decline, affecting both ecosystem health and carbon accounting. The study also highlights the need to better understand temperature thresholds for redwood survival. For those tracking climate impacts on forests, this paper provides the first direct evidence of heat-related photosynthesis decline in coast redwoods. It underscores how warming can undermine natural carbon sinks, even in relatively cool coastal habitats.
