Trees may store less carbon than climate models suggest
Top line
Trees store less carbon than climate models suggest because photosynthesis does not always lead to sustained wood growth, particularly under heat and drought conditions.
Summary
Research conducted at 137 sites across the United States challenges the common assumption in climate modeling that photosynthesis directly equates to long-term carbon sequestration through wood growth. Scientists discovered that trees often stop producing wood months before they stop photosynthesizing, a phenomenon particularly evident in regions experiencing heat and drought. Because current models often rely on photosynthesis rates to estimate carbon storage, they may be overestimating the ability of forests to act as a long-term carbon sink in a warming world, especially as environmental stressors continue to exacerbate the decoupling of these biological processes.
Highlights
- A study of 137 sites across the United States reveals that trees often stop growing wood months before they cease photosynthesis.
- Current climate models predominantly rely on the assumption that photosynthesis is directly proportional to wood growth, which leads to potential overestimation of long-term carbon storage.
- In the eastern United States, researchers found that approximately 36% of annual carbon uptake occurred after wood growth had already ceased in late summer.
- In California, approximately 26% of annual carbon uptake occurred after wood growth had stopped.
- Wood growth is highly sensitive to heat and aridity; growth activities stop almost immediately under stressful environmental conditions, whereas photosynthesis continues at a reduced rate.
- As global temperatures rise and extreme weather events like heatwaves and droughts become more frequent, the decoupling of photosynthesis and wood production is expected to intensify.
- Forests currently represent the vast majority of human efforts to remove carbon dioxide from the atmosphere, as technological carbon removal methods account for only 0.1% of global sequestration.
- The findings suggest that Earth system models must be recalibrated to account for the actual allocation of carbon toward woody tissue versus transient foliage to accurately forecast future carbon sequestration capacity.
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