UFZ researchers Prof. Andreas Huth and Dr. Rico Fischer led a new study in collaboration with the Helmholtz Centre for Environmental Research (UFZ) and the University of Maryland looking at the carbon output of forest fragmentation. Recently published in Nature Communications, the team found that fragmentation of formerly contiguous areas of forest raises carbon emissions by one third.
"We have known for a long time that not only the complete loss of rain forests can exacerbate climate change," explains Andreas Huth. Fragmenting a larger forest area into several smaller ones impacts the vegetation at the edges because trees are exposed to an unfavourable micro-climate. Trees on the edges (quantified as the outer 100 meters periphery) face more direct solar radiation, higher wind speeds and lower air humidities than trees on the interior of a forest. They also dry out more faster. "Large trees suffer most from this development, because they are reliant on a good supply of water," explains Huth.
This correlates to a larger output of carbon dioxide, when compared to non-fragmented areas. Responsible for this are the micro-organisms that break down dead trees, which release large amounts of CO2. The other factor is a matter of absence; there are fewer living trees that remove CO2 from the air.
The study explains their methods and results succinctly: “Here we combine high-resolution (30 m) satellite maps of forest cover with estimates of the edge effect and show that 19% of the remaining area of tropical forests lies within 100 m of a forest edge. The tropics house around 50 million forest fragments and the length of the world’s tropical forest edges sums to nearly 50 million km. Edge effects in tropical forests have caused an additional 10.3 Gt (2.1–14.4 Gt) of carbon emissions, which translates into 0.34 Gt per year and represents 31% of the currently estimated annual carbon releases due to tropical deforestation. Fragmentation substantially augments carbon emissions from tropical forests and must be taken into account when analysing the role of vegetation in the global carbon cycle.”
The team found that 19 percent of all the world's tropical forests are less than one hundred meters away from the edge of the forest, and humans are accountable for 84 percent of the total amount of tropical forest fragmentation.Clearing tropical forests gives rise to carbon emissions of around one gigatonne (1000 million tonnes) every year. Now we know that fragmentation of the remaining forests increases this amount by almost one third. Fragmentation also affects species biodiversity.
The research team hopes that future climate talks will include their results in plans to curb carbon emissions. "This effect has not been taken into consideration at all in the IPCC reports to date," complains Huth. Not only must we focus on decreasing deforestation, but also fragmentation.