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Tree trunks emit methane, study says


Trees help us tackle greenhouse gas emissions, but it turns out that these trees may also be involved in contributing to global warming by adding methane to the environment.

This is the finding of a new study published by scientists at University of Delaware who have for the first time shown that tree trunks in upland forests are actually emitting methane rather than storing it.

Methane is a potent greenhouse gas – 25 times stronger than carbon dioxide – and that’s one of the reasons why scientists are trying to figure out all the sources of methane and ‘sinks’ where this greenhouse gas is stored. There have been studies that have established Upland forest soils has sink of methane, but it turns out that tree trunks in the forests are counteracting this effect says the new study published in the scientific journal Ecosystems.

The study and findings will be vital in filling up the gaps in methane budgets and environmental processes in global ecosystem models.

For the study researchers tested a cluster of trees, soil and coarse woody debris (CWD)–dead wood lying on the forest floor in various stages of decomposition–to measure fluxes of methane and carbon dioxide in a 30-acre area of upland forest at Fair Hill Natural Resources Management Area in nearby Cecil County, Maryland.

The researchers used a state-of-the-art greenhouse gas analyzer based on laser absorption technology, called Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS), which looks similar to a proton pack from the movie “Ghostbusters.”

In terms of carbon dioxide, research on the fluxes of tree trunks, known as stem respiration, and soil, known as soil respiration, has been done for decades, but research to determine the importance of carbon fluxes with regard to CWD still lags behind.

For methane, however, it’s a different story. While studies have been done on methane fluxes in connection to soils, which usually consume the methane and are considered methane sinks, there are very few that deal with CWD and tree trunks in upland soils.

Tree trunks and methane fluxes

While tree trunks have been known to release carbon dioxide, this research showed that they were also releasing methane.

Overall, the tree trunks acted as a source of carbon dioxide and as a small source of methane, but the magnitude of gases emitted varied with the species.

Tulip poplar was one species that released a lot of methane and carbon dioxide, whereas beech trees released the most methane within the forest but emitted very little carbon dioxide.

Temperature threshold

Temperature also played a key role in regulating the magnitude of the fluxes.

Researchers said it’s hard to develop a temperature relationship with methane because there are two processes that oppose each other.

They found that beyond a threshold of 17 degrees Celsius for soil temperature, the variability of methane consumption expands dramatically.

Soil hot spots

As for where the methane originated, Warner said it’s still a science frontier, but this study provides enough clues to give the researchers some theories.

The first one is that methane is produced in hot spots in the soil.

Scientists explain hot spot as a place where conditions are conducive to methane production and then that methane is sucked up by the tree roots, transported through its vascular system and released out of its trunk.

The other mechanism that could be causing methane fluxes from trunks is internal rotting or infection inside the tree, which produces an environment where methanogenic bacteria can survive and then methane diffuses out of the tree.