A new study of oak trees in the eastern US and California found that trees continue absorbing carbon well after they stop growing. Growth stops in mid-summer due to hot and dry conditions, but photosynthesis keeps running into autumn. In eastern sites, 36% of annual carbon uptake happened after growth ended. In California, it was 26%. The carbon absorbed after growth stops mostly does not become durable woody biomass. Instead, it goes into starch, leaves, roots, or is released through respiration. This means forests may store less carbon long-term than current climate models assume. The gap between photosynthesis and growth widens in years with extreme wet-dry swings, which are becoming more common with climate change. The research used satellite data, CO2 sensors, growth monitors, and tree ring records across 137 sites. The lead author said most models assume photosynthesis equals growth, but the data shows that is not the case. The team is now studying whether the pattern holds in other tree species and regions.
