Shown are forest fragments of the Brazilian Atlantic Forest in the North-East of Brazil, surrounded by sugar cane plantations.Mateus de Dantas de Paula

Degradation and fragmentation along the edges of tropical forests worldwide results in an increased 0.2 billion tonnes of carbon released into the atmosphere every year, says a new study.

Rainforests act as natural carbon molecule storage systems (carbon sinks) thanks to the photosynthesis process of trees and plants. The healthier and more vast a forest, the more carbon it can absorb from Earth's atmosphere and store. Because atmospheric carbon is a major contributor to the greenhouse effect, and subsuquently climate change, the health of the planet's forests is critical.

Fragmentation of the forest exposes a greater peripheral area of forest edges to tough climate conditions, causing plants to release more carbon into the atmosphere as they work to survive or decompose after death.

According to scientists of the Hemholtz Centre for Environmental Research (UFZ):

  • More than a fifth of the carbon released from deforestation has been missing from calculations of the IPCC (Intergovernmental Panel on Climate Change) due to forest fragmentation in Brazil.
  • Due to peripheral fragmentation effects, almost 600 million additional tonnes of carbon are lost into the atmosphere from the Amazon rainforest over ten years.
  • In the heavily fragmented north-eastern Brazilian coastal tropical forest Mata Atlântica (Brazilian Atlantic Forest), 68 million tonnes of carbon are lost due to forest fragmentation.

The scientists looked initially at the percentage loss of carbon in Brazil's forest borders after the deforestation of the surrounding area. The losses of the differently fragmented and differently sized forest areas were determined in comparison to large, unchanged tracts in the tropical rainforests in the Amazon and in the Mata Atlântica.

For their study they defined a strip of 100 metres that runs from the edge of the forest into the inner forest as the peripheral area.

Climate Stress

Trees at the newly created edges of the forest receive strong sunlight that leads to temperature increase and are also subject to the wind. The stress becomes large and the larger specimens die off. The study thus found that these trees can't store as much carbon as healthy trees in the centre of the forest.

The team next determined the percentage loss of carbon in forest fragments of different sizes.
The UFZ scientists used high-resolution satellite images to analyse how the tropical rainforest is spatially distributed in the Amazon region and the coastal tropical forest.

According to the records, the coastal tropical forest with a total of 11% of its original surface area only takes up 157,000 square kilometres and is split into 245,173 fragments. Around 90% of the forest remains are smaller than 100 hectares, which means that they have many edges.

The 3.1 million sq km of the Brazilian part of the rainforest in the Amazon consists of over 300,000 forest fragments. However, the peripheral areas only amount to about 7% of the entire area. This means that the additional loss of carbon in the entire rainforest of the Amazon due to the peripheral effects amounts to approximately 600 million tonnes in ten years.

Global Scene

Looking at the global scenario, there are currently 830 billion tonnes of carbon in the atmosphere, which is set to increase by four billion tonnes every year. A quarter of this increase is attirbuted to deforestation around the globe.

The UFZ model indicates that 10% of the forest areas in the tropics worldwide lie at the edges of forests and hence, the degradation here results in an increase of up to 0.2 billion tonnes of carbon getting into the atmosphere per year.

Deforestation in Brazil has been in the spotlight recently with reports showing a 29% degradation of forests in a single year. Illegal logging has been the main cause.

Atmospheric CO2 was at 396 parts per million (ppm) in 2013, recording a 142% rise over the levels in 1750, before the start of the industrial revolution. Between 1990 and 2013 there has been a 34% increase in emissions.