The bigger role of trees in global carbon cycling

Forests play a crucial role in absorbing not only CO2 but also methane, according to a new study in Nature. Field studies reveal that the woody surfaces of upland trees are a substantial global sink for methane, a potent greenhouse gas.

Trees influence soil methane flux through its influence on soil properties and hydrology and have been shown to emit methane from the lower part of their trunks, but the new study suggest that methane is being absorbed higher up on the stem, possibly due to methane absorbing bacteria. A key limitation of the new study studies is that the methane measurements were taken mainly below 2 m, when it is highly likely that the uptake is different farther up the tree trunks.

Future research should focus on measuring methane uptake higher up the trees, from trunks, smaller branches, shoots, and leaves, and in various environments. Long-term, high-frequency measurements will help reveal patterns in tree methane flux and enhance our understanding of trees' role in the global methane budget.

This discovery of stems taking up methane, could help resolve the discrepancy in global methane emission estimates. In such estimates, results are about 30% higher in bottom-up models based on data driven modelling, compared to top-down models based on atmospheric measurements and inverse modelling. This suggests either an overestimation of emissions or an underestimation of sinks in the bottom-up estimates, argues Patrik Vestin.

This text is a review from the news and views article “Forests don’t just absorb CO2 — they also take up methane” by Patrik Vestin. Read the full article in Nature

Nature 631, 744-745 (2024)

doi: https://doi.org/10.1038/d41586-024-02270-3