Updated

Updated · ScienceDaily · Jul 10

Oak Trees Keep Absorbing 36% More Annual Carbon After Growth Stops, Challenging Forest Storage Models

Updated

Updated · ScienceDaily · Jul 10

Oak Trees Keep Absorbing 36% More Annual Carbon After Growth Stops, Challenging Forest Storage Models

Q: Trees are absorbing CO2 but not growing. Where is all that 'extra' carbon actually going?

Most of that “extra” carbon is not becoming new wood. The Columbia Climate School study found that after oak growth stops, trees keep photosynthesizing and redirect much of the carbon into short-lived uses, temporary storage, roots, and the soil rather than long-term woody biomass. Researchers say the carbon is used to keep the tree functioning: maintaining living cells, fueling respiration and other metabolic processes, and helping the tree survive stress and winter. Some is stored inside the tree as non-structural carbohydrates such as sugars and starch, which can be drawn on later to support the next season’s growth. Some of the carbon also goes into tissues other than trunk wood, including leaves, fruits, and especially new roots. Under hot, dry conditions, this shift becomes more pronounced because wood growth depends on internal water pressure, which drops quickly in drought, while photosynthesis can continue at a reduced rate. Another share likely moves belowground. Trees release carbon-rich compounds through their roots that feed microbes and mycorrhizal fungi, support nutrient uptake, and help with defense against pests and disease. Some of that carbon may remain in soils for a time, but much of it cycles back to the atmosphere faster than carbon locked into trunks and branches. That is why the finding matters for climate forecasts: forests may still absorb CO2, but a smaller fraction may end up stored for decades in wood than many models assume.

3 articles · Updated · ScienceDaily · Jul 10

A Science Advances study found oak trees keep taking in CO2 for months after annual wood growth ends, weakening a core climate-model assumption that more photosynthesis directly means more long-term carbon storage.
At 137 oak forest sites, eastern oaks typically grew from May to July but photosynthesized into October, with 36% of annual carbon assimilation occurring after late-summer growth stopped; California oaks showed the same pattern at 26%.
Hot, dry conditions appear to drive the split: trunk growth depends on internal water pressure that drops quickly in arid weather, while photosynthesis continues at a reduced rate.
That extra carbon may go to leaves, roots, starch and cell maintenance rather than wood, suggesting forests could lock away less carbon than many models project in a warmer, CO2-richer world.
Researchers also found the disconnect widened in years with sharper wet-dry swings, indicating rising climate variability could make the pattern more common beyond oaks.