Oak trees continue absorbing carbon dioxide through photosynthesis well after they stop adding new growth rings each year, according to research that upends long-held assumptions about how trees store carbon.
Scientists previously believed that once a tree's annual growth ceased, its photosynthetic carbon uptake dropped sharply too. The new work demonstrates these processes operate independently. Trees keep fixing CO2 from the atmosphere even when wood production halts for the season, meaning they accumulate more carbon than growth rings alone would suggest.
This distinction matters for climate modeling. Current forest carbon projections rely heavily on measurements of tree ring width as a proxy for carbon sequestration. If trees absorb significantly more CO2 than their rings indicate, existing estimates of forest carbon storage capacity may be substantially underestimated.
The finding also carries implications for understanding how forests respond to climate change. As warming alters growing seasons and stress patterns, the decoupling of photosynthesis from wood formation could shift where and how much carbon forests store. Warmer conditions might suppress growth while leaving photosynthetic activity intact, or vice versa. This creates uncertainty about whether forests will continue functioning as reliable carbon sinks in future climates.
The research focused on oak trees specifically, though researchers suggest the mechanism likely applies to other tree species. The study reveals that tree physiology is more complex than traditional dendrochronology, the field that uses growth rings to reconstruct past climates and carbon cycles, assumes.
Scientists now face the task of refining forest carbon models to account for this decoupling. Monitoring only growth rings provides an incomplete picture of atmospheric carbon uptake. Methods that directly measure photosynthetic rates or track stable isotopes in wood may offer better accuracy. The work underscores how foundational assumptions in climate science sometimes need revision as new evidence emerges from closer examination of natural systems.