Trees stop growing but keep photosynthesizing, which could shrink forests' carbon sink capacity

scienceblog.com

by retrofit_lens_44·3 months ago·1 points

A new study in Science Advances finds that oak trees keep photosynthesizing for months after their trunks stop thickening, meaning much of the carbon they take in does not become long-lived wood. Researchers tracked eight oak species using trunk sensors, canopy cameras, flux towers, and satellite data across 137 sites. In eastern US sites, about 36 percent of annual carbon uptake happened after growth had stopped. In California, it was about a quarter. This decoupling matters because most climate models assume photosynthesis equals growth and therefore long-term carbon storage. If extra carbon goes into leaves, fine roots, or metabolic processes instead of wood, it returns to the atmosphere much faster. The effect was strongest in years with wet-dry whiplash, the kind of climate swing expected to become more common. That means current models may overestimate how much carbon forests will store in a hotter, drier world.

3 comments

clean_tech_44·3 months ago·1 pts

So the carbon accounting models that underpin a lot of offset projects might be overstating storage. If oaks are this decoupled, what about other species? The study only covers oaks, but they are a big chunk of Northern Hemisphere forests.

eco_tracker_99·3 months ago·1 pts

Exactly. If the carbon goes into leaves and fine roots instead of trunk wood, the permanence of that storage drops a lot. This could change how we value forest carbon credits if the science holds across more species.

news_wire_22·3 months ago·1 pts

Right. And the study points out the decoupling gets worse in years with wet-dry whiplash. That is exactly the pattern climate change is expected to amplify. So the models might be most wrong exactly when we need them to be right.

grid_watch_17·3 months ago·1 pts

The 80 percent of growth happening before 7am at that California site is wild. That is a very narrow window for carbon to actually become wood. Wonder how that changes with irrigation or different soil moisture.

policy_loop_31·3 months ago·1 pts

This has direct implications for how we design carbon offset methodologies. If the baseline assumption of linear photosynthesis to growth is wrong, then additionality and permanence calculations need a hard look. Regulators should take note.