For years, climate scientists and forest ecologists have operated under a straightforward assumption: trees absorb carbon dioxide through photosynthesis, and that carbon gets stored in wood as the tree grows. When growth stops, so should carbon uptake. A new study published in Science Advances by researchers at the Columbia Climate School has overturned this neat picture. Using satellite imagery and ground-based instruments, the team tracked oak trees over multiple growing seasons and found that photosynthesis continued pumping carbon into the trees long after annual wood production had ceased.
The researchers focused on temperate oak forests in the northeastern United States, measuring both photosynthesis rates and wood growth at high temporal resolution. What they found was a significant temporal decoupling: the trees absorbed carbon dioxide for weeks beyond the point where new wood cells stopped forming. During this extended period, the carbon appeared to be allocated to non-structural carbohydrate reserves — essentially stored sugars and starches that the tree can draw on later for maintenance, defense, or growth in the following season.
This finding has important implications for how scientists model the global carbon cycle. Most current climate models assume a tight coupling between photosynthesis and tree growth, meaning they may be underestimating how much carbon forests actually capture over a full year. If trees across different species and ecosystems show similar decoupling patterns, the world's forests could be a larger carbon sink than currently calculated — a potentially significant factor in climate projections.
The study also raises questions about forest management strategies. If carbon storage in non-structural reserves is substantial, then harvesting trees at the end of the growing season could release more carbon than expected, as those reserves decompose or burn. Conversely, allowing forests to mature and accumulate carbon in both wood and reserves could enhance their climate mitigation value beyond what growth-based models predict.
Knowledge takeaway: Oak trees continue absorbing carbon dioxide for weeks after annual wood growth stops, decoupling photosynthesis from growth; the extra carbon goes into non-structural carbohydrate reserves rather than wood; current climate models may underestimate forest carbon uptake by assuming tight photosynthesis-growth coupling; this finding affects forest management and carbon accounting strategies.