18 Dec 2012

Tropical trees are largest emitter of methane in their ecosystem

Researchers at The Open University have found that trees in Bornean rainforests emit more methane than any other element of the ecosystem, which provides a new understanding about sources of this powerful greenhouse gas from tropical ecosystems.

In a paper titled Trees are major conduits for methane egress from tropical forested wetlands by Dr Vincent Gauci and Sunitha Pangala, published in New Phytologist on 18 December, the researchers announced new findings which show that trees in tropical peat forests of Southeast Asia release more methane through their stems than is emitted from the soil surface.

Sunitha Pangala, final year PhD student at The Open University’s Centre for Earth, Planetary Space and Astronomical Research, and lead author on the paper said: "This is the first study to measure methane release from tree stems in tropical peat swamps and evaluate its importance at an ecosystem level. Our research establishes that trees in tropical peat swamps are the largest emission pathway of methane in that ecosystem."

Previously it was thought that methane was only emitted via diffusion and bubbles at the wetland surface. The team measured methane emissions from healthy tree stems in a tropical forested peatland in the upper Sebangau River catchment in Borneo. They found significant quantities of methane being released from the stems of seven of the eight tree species studied. They estimated up to 87% of the methane are released from tree stems, highlighting that the previous methane emission inventories of this ecosystem may have been severely underestimated.

"This work challenges our previous understanding of how these ecosystems exchange methane with the atmosphere and adds another piece to the tropical methane emission puzzle,” said Dr Vincent Gauci, Senior Lecturer, Earth Systems, and the project’s leader. "It further shows that for wet tropical forested ecosystems, the like of which span south America, Africa and southeast Asia, researchers may have been missing most of the methane emitted from these ecosystems if they neglected to measure tree stem emissions.”

According to Dr Gauci, since satellite images showed that there was more methane emitted from tropical ecosystems than measurements at the wetland surface would suggest, researchers have been trying to resolve the puzzle and identify causes behind this apparent discrepancy.

A pdf of the paper, Trees are major conduits for methane egress from tropical forested wetlands is available from the Media Relations team.

Editor's notes
The work involved Dr Vincent Gauci and Sunitha Pangala of The Open University; Dr Sam Moore of Oxford University; and Dr Ed Hornibrook of Bristol University.

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