More carbon is being drawn from the atmosphere by city trees and soil

Although they do not have lungs like us, the soil and trees constantly breathe in and out. Trees absorb CO2, release oxygen through photosynthesis, and store carbon in their trunks. When the leaves fall to the ground, soil microbes decompose them and other organic matter, releasing carbon dioxide.

Forests store more carbon dioxide than they emit, which is excellent news for us: forests absorb approximately 30% of the carbon emissions from burning fossil fuels, a phenomenon is known as the terrestrial carbon sink.

"That's CO2 that isn't in the atmosphere," says Lucy Hutyra, a biogeochemist and ecologist at Boston University. "Because of the terrestrial climate sink, we are not feeling the full effects of climate change. These forests provide invaluable services to our planet."

Hutyra has been studying what happens to the planet's "lungs" when extensive forests are cut down into smaller patches, a process known as forest fragmentation.

"We think of forests as big landscapes, but they're cut up into all these little details because of the human world," tell Hutyra, a BU College of Arts & Sciences Earth and environment professor. 

Forests are being cut into smaller parcels to make way for roads, buildings, agriculture, and solar farms, one of the leading causes of forest loss in Massachusetts. These forest changes result in more areas known as forest edges, literally, the trees at the forest's outermost edge.

It has long been assumed that forest edges release and store carbon at the same rates as forest interiors, but Hutyra and her colleagues at BU have discovered that this is not the case. Instead, soils and trees near the edges of temperate forests in the Northeast United States are behaving differently than those further away.