Trees' Carbon Storage Less Than Feared?

New research indicates that trees might not absorb as much atmospheric carbon dioxide as previously believed. A study examining 137 sites across the United States found that tree growth often ceases months before the end of the photosynthesis period each year.

This observation challenges existing climate models, which frequently assume that photosynthesis directly translates into wood growth. Researchers noted that in eastern US forests, approximately 36% of annual carbon uptake happened after wood growth had stopped. Similarly, in California, this figure was around 26%.

Detailed measurements at four locations revealed that wood growth is particularly sensitive to aridity and temperature. As global temperatures rise, leading to more frequent heatwaves and droughts, these conditions are becoming rarer. This restricts the periods during which trees can effectively grow and store carbon.

Scientists are now investigating if this separation between photosynthesis and wood growth occurs in other tree species and regions. They emphasize that the capacity of forests to act as long-term carbon sinks depends on how much absorbed carbon is directed towards wood growth versus other uses, like foliage. If more carbon is used for transient processes, the effectiveness of forests as carbon sinks could diminish.