Tropical forest fragmentation is progressing at an alarming pace

The fragmentation of tropical rainforests is progressing much more quickly than expected, and the consequences for the global carbon cycle are alarming, according to a new study from the Helmholtz Centre for Environmental Research (UFZ). 

By analyzing high-resolution satellite data, the researchers were able to accurately measure even the smallest change in tropical forest cover. The analysis has exposed a previously unknown increase in fragmentation that affects nearly one third of the world’s rainforest area. 

The experts report that as a result of increased tree mortality, large amounts of carbon are being released at the edges of fragmented forests. The only way to slow these emissions is through lower rates of deforestation.

The researchers used satellite data to pinpoint where intact tropical forests may still exist in Central and South America, Africa, and Southeast Asia. They found that the number of isolated forest areas increased by just over 20 million to 152 million between 2000 and 2010. This extent of tropical fragmentation is especially concerning because it has also increased the proportion of forest edges in the total forest area. 

“This situation has deteriorated so much that now almost one third of the world’s tropical forest areas are in edge areas. If deforestation is not stopped, this trend will continue,” said study lead author and Dr. Rico Fischer. 

The accelerated rate of fragmentation was mainly found in the tropics of Africa, where the number of forest fragments increased from 45 to 64 million within 10 years. The study is one of the most detailed of its kind to investigate the carbon balance of tropical forest edges.

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

More trees die at the forest edge because they are more stressed there than trees that are in the protected interior of a forest. “This means that large amounts of carbon are released into the atmosphere at the edges of tropical forests,” said Dr. Fischer.

The researchers estimated the carbon emissions caused by increased tree mortality for all forest edges. They determined that carbon emissions associated with forest fragmentation increased from 420 million tons in 2000 to 450 million tons in 2010. 

“In the tropics, deforestation alone releases around 1,000 to 1,500 million tonnes of carbon every year. 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,” said study co-author Dr. Andreas Huth. 

The fragmentation of tropical forests also affects biodiversity. The researchers found that the distances between the forest fragments are becoming progressively larger. 

“This makes the long-term survival of animal species such as the jaguar, which depends on large, connected forest areas, more difficult,” said study co-author Dr. Franziska Taubert.

“If the current dynamics of fragmentation continue at a constant rate, forest edges will release 530 million tons of carbon annually by 2100. Only if deforestation of the rainforest is stopped from 2050 onwards can emissions be limited to a maximum of 480 million tons of carbon,” said Dr. Fischer.

The study is published in the journal Science Advances.

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By Chrissy Sexton, Earth.com Staff Writer