The surface area of forest edges are increasing as tropical forests become increasingly fragmented. According to a new study, published Wednesday in the journal Science Advances, forest edges accelerate carbon emissions.

To better understand how fragmentation is impacting tropical forests, researchers used a complex algorithm to analyze high resolution satellite images of forests in Central and South America, Africa and Southeast Asia captured between 2000 and 2010.

The algorithm showed that, in just a decade, the number of isolated forests increased by 20 million. As a result, the size of forest edges increased by several million acres.

"This situation has deteriorated so much that now almost one third of the world's tropical forest areas are in edge areas," study lead author Rico Fischer said in a press release.

"If deforestation is not stopped, this trend will continue," said Fischer, a forest modeler at the Helmholtz Center for Environmental Research in Germany.

To measure the effects of these changes on a forest's carbon cycle, scientists designed detailed models using biomass data captured via remote sensing.

"The edge, unlike the forest interior, is subject to direct sunlight. It is more exposed to the wind," Fischer said. "Humidity also decreases in the edge areas. The altered micro-climate particularly damages the large trees that depend on a good water supply."

Remote sensing data confirmed that the loss of large trees along the edge leads to decreases in vegetation and biomass. With fewer large trees, less carbon is pulled from the atmosphere.

Additionally, an uptick in tree death leads to higher rates of decomposition. As microorganisms break down dead trees, carbon is released in the atmosphere.

Using the new model, researchers determined annual carbon emissions along forest edges increased by 30 million tons between 2000 and 2010.

"In the tropics, deforestation alone releases around 1,000 to 1,500 million tons of carbon every year," said co-author Andreas Huth, professor of biophysics at UFZ.

"If we consider the additional effect of the forest edges, this is a worrying finding because the tropical rainforest should actually be a carbon sink -- and not a carbon source," Huth said.

Further simulations showed that forest edges will continue to grow in size even if deforestation and fragmentation rates slow, diminishing the ability of tropical forests to trap carbon and slow climate change.

"If the current dynamics of fragmentation continue at a constant rate, forest edges will release 530 million tons of carbon annually by 2100," Fischer said.

"Only if deforestation of the rainforest is stopped from 2050 onwards can emissions be limited to a maximum of 480 million tons of carbon," Fischer said.

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