Temperate Forest Methane Sink Diminished by Tree Emissions

Upland forests offset soil methane sinks by 1% to 6% through stem emissions.

The Science

Upland forest soils remove methane from the atmosphere and are represented in global budgets as net methane sinks. However, this study demonstrates that upland trees can also emit methane.

The Impact

Studies of methane fluxes in upland forests have focused on exchanges between the atmosphere and soils, but the scientists conclude that methane fluxes across tree surfaces are also potentially important for upland forest methane budgets.

Summary

Upland forests remove methane from the atmosphere and are represented in global budgets as net methane sinks. However, this view is based almost entirely on measurements of methane exchange across forest soil surfaces, with little attention to the exchange of methane across plant surfaces. Here the team report that methane is emitted from the stems of dominant tree species in a temperate upland forest. The source of the methane emitted from these trees is uncertain but may include transport in the transpiration stream from anoxic groundwater, or methane produced inside the tree itself. High-frequency measurements revealed diurnal patterns in the rate of tree-stem methane emissions that support a groundwater source. A simple scaling exercise suggested that tree emissions offset 1% to 6% of the growing season soil methane sink, and the forest may have briefly changed to a net source of methane to the atmosphere due to tree methane emissions.

Principal Investigator

Patrick Megonigal
Smithsonian Environmental Research Center
megonigalp@si.edu

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This study was supported primarily by the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research (grant DE-SC0008165) within the U.S. Department of Energy Office of Science. The components of an automated flux system was developed with funds from the National Science Foundation’s (NSF) ERC MIRTHE (EEC-0540832).

References

Pitz, S. A., and J. P. Megonigal. "Temperate forest methane sink diminished by tree emissions". New Phytologist 214 (4), 432–439  (2017). https://doi.org/10.1111/nph.14559.