Trees are biggest methane 'vents' in wetland areas – even when they're dry

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Researchers at the University of Birmingham say that most of the methane gas emitted from Amazon wetlands is vented into the atmosphere via tree root systems.

In a study published in the Philosophical Transactions of the Royal Society A, it was found that trees growing on the floodplains of the Amazon basin emit far more methane than soil or surface water.

Methane comes from wetlands and is the second most important greenhouse gas. Modelling assumes that the gas is only produced when the ground is completely flooded and underwater, but a lot of research is being carried on into that.

In wetlands where there are no trees, methane would typically be consumed by the soil on its way to the surface, but in forested wetlands, the tree roots could be acting as a transport system for the gas.

Even though methane is produced in soil and water that is several meters below ground level, it can escape via this route.

Existing models could be significantly underestimating the extent of methane emissions in the Amazon basin.

To test the theory, the team measured across three plots on the floodplains of three major rivers in the central Amazon basin. The same trees were monitored at four different times over the course of the year to see how they responded to the flood. Methane emissions were measured using a portable greenhouse gas analyser and then calculations were done to scale the findings up across the Amazon basin.

The team estimate that nearly half of global tropical wetlands methane emissions are funneled out by trees, with the unexpected result that trees are also important for emissions at times when the floodplain water table sits below the surface of the soil.

The results show that current global emissions estimates are missing a crucial piece of the picture. We need to take into account the role trees play in the emission of methane.

The team was led by the University of Birmingham and included researchers from other universities.

The non-flooded Amazon trees are a significant methane source in the region. There is a DOI: 10.1098/rsta.

The Royal Society A has a journal.

The biggest methane'vents' in wetlands are trees, even when they're dry.

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