More trees, less global warming? Not exactly

Trees are considered as one of our biggest natural allies in the war against global warming, but in a new twist, scientists have found that the army of green is spewing out methane.

The University of Delaware study is one of the first in the world to show that tree trunks in upland forests actually emit methane rather than store it, representing a new, previously unaccounted source of this powerful greenhouse gas.

Methane is about 25 times stronger than carbon dioxide, with some estimates as high as 33 times stronger due to its effects when it is in the atmosphere.

Because of methane's global warming potential, identifying the sources and "sinks" or storehouses of this greenhouse gas is critical for measuring and understanding its implications across ecosystems.

Upland forest soils usually take up and store methane, but this effect can be counteracted by methane emissions from tree trunks, the research team from UD's College of Agriculture and Natural Resources found.

"We believe our work can help fill in some gaps in methane budgets and environmental processes in global ecosystem models," said study leader Rodrigo Vargas.

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.

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

The study is published in the scientific journal Ecosystems.