Worldwide carbon emissions due to fragmentation of tropical forests. (a) Colours represent the estimated carbon losses for each fragment, setting edge depth d to 100 m and relative carbon losses in forest edges e to 50%. Insets illustrate exemplary regional carbon emissions for (b) tropical America (89.752 W, 13.515 N), (c) tropical Africa (17.206 E, 4.499 S) and (d) tropical South-East Asia (103.898 E, 3.091 S). Graphic: Brinck, et al., 2017 / Nature Communications

By Morgan Erickson-Davis
31 March 2017

(Mongabay) – The earth’s forests have been broken into around 50 million fragments, the edges of which add up to a length that would make it a third of the way to the sun and which increase annual tropical deforestation carbon emissions by 31 percent. This, according to a new study published recently in Nature Communications that reveals forest fragmentation may be much more destructive than previously thought.

A few hundred years ago, most large tropical forests stood vast and largely undisturbed. But since then, agriculture and extractive industries have moved in, whittling away forests to make room for cattle pasture and soy fields, palm oil plantations and acacia concessions.

Today, owing primarily to human pressures, many of the world’s tropical forests exist as a collection of remnants. The Atlantic Forest is one of these. Once covering a huge swath of the eastern coast of Brazil and into Paraguay, Uruguay, and Argentina, the Atlantic Forest (called Mata Atlântica in Portuguese) has largely disappeared, and some researchers estimate just 3.5 percent may still remain – mostly as fragments interspersed in an expanse of pasture and cropland.

Research has shown that forest fragmentation can have dire effects on wildlife, leading to higher extinction rates than if a forest is simply reduced in size while remaining in one piece. But how fragmentation affects carbon emissions is something that scientists haven’t been able to grasp – until now.

Enter researchers with the Helmholtz Center for Environmental Research and the University of Maryland. They drew on previous studies that showed tree mortality in tropical forests was affected significantly by where they trees were, with trees on the edges of forests having double the chances of dying in a given year. This is because vegetation at edges is exposed to harsher conditions like stronger wind, more intense solar radiation, and lower humidity than trees in the interior of forests. The research showed that this wasn’t only affecting periphery trees, but also tree as far as a hundred meters into forests.

“Large trees suffer most from this development, because they are reliant on a good supply of water,” said Andreas Huth of the Hemholtz Center, coauthor of the study released this week. [more]

Forest fragmentation may be releasing much more carbon than we think


ABSTRACT: Deforestation in the tropics is not only responsible for direct carbon emissions but also extends the forest edge wherein trees suffer increased mortality. 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.

High resolution analysis of tropical forest fragmentation and its impact on the global carbon cycle

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