- In addition to having severe repercussions for animals like jaguars and tigers that require vast tracts of connected habitat, forest fragmentation has a big carbon footprint.
- A new physics-based study finds fragmentation of tropical forests may be reaching a threshold past which fragmentation will shoot up sharply. At this threshold, even a relatively small amount of deforestation could lead to dramatic fragmentation – and significant habitat loss and greenhouse gas emissions.
- The team calculated that at current deforestation rates, the number of fragments will increase 33-fold in Central and South America by 2050, and their average size will drop from 17 hectares to 0.25 hectares.
Deforestation in the tropics is caused by many different human activities that vary in intensity depending on location. In South America, industrial agriculture is the big driver of deforestation while smallholder farming is pockmarking Congo rainforest and logging for high-value timber species is having devastating effects on the forests of mainland Southeast Asia.
Yet, despite the diversity of these activities, a new study published this week in Nature shows they have had a surprisingly similar overall impact on the world’s tropical forests – an impact that appears to be reaching a “critical point” past which the consequences may be catastrophic.
The issue here is fragmentation. As humans move in and cut down trees, remaining forest is fragmented into smaller and smaller chunks that are increasingly farther away from each other. In addition to having severe repercussions for animals like jaguars and tigers that require vast tracts of connected habitat, forest fragmentation has a big carbon footprint.
Research published in 2017 revealed that the world’s tropical forests are currently cut up into around 50 million fragments, and their edges add up to about 50 million kilometers – which put together would make it about a third of the way from Earth to the sun. The study found trees at these fragment edges are much more likely to die than those in the middle of forests, potentially adding 31 percent more greenhouse gas emissions to the atmosphere.
But what is the overall impact of these fragments, and what will they look like in the future? To find out, researchers at Germany’s Helmholtz Centre for Environmental Research (UFZ) used physics to mathematically describe the fragmentation of tropical forests on a global scale. The team identified fragments via high-resolution satellite data that detects gaps in tree canopies and found fragmentation patterns in the world’s thee main rainforest regions – Africa, Southeast Asia and South/Central America – fit physic’s “percolation theory.”
“[Percolation theory] states that in a certain phase of deforestation the forest landscape exhibits fractal, self-similar structures, i.e. structures that can be found again and again on different levels,” said biophysicist Andreas Huth, a coauthor of the study.
The team discovered that forest fragments had similar sizes in all three regions, despite being caused by different activities. In Central and South America, they found 11.2 percent of forest fragments are smaller than 10,000 hectares; in Africa it was 9.9 percent, and 9.2 percent in Southeast Asia.
“This is surprising because land use noticeably differs from continent to continent,” said Dr. Franziska Taubert, mathematician and lead author of the study
The team’s results suggest that forest fragmentation is close to what they call a “critical point of percolation” in all three major rainforest regions. In physics, a critical point of percolation is also called a phase transition and happens when something is at the threshold of turning from one form into another – like when liquid water boils and turns into vapor.
For forests, the critical point of percolation is the point at which the rate of fragmentation will shoot up dramatically. And the researchers found that the current number and size of fragments suggest that rainforests in all three regions are close to this critical point. They write that near this point, even “small additional amounts of forest loss in the near future would lead to a strong increase in the number of forest fragments.”
The team calculated that at current deforestation rates, the number of fragments will increase 33-fold in Central and South America by 2050, and their average size will drop from 17 hectares to 0.25 hectares.
The researchers say that in order to turn things around, fragmentation needs to slow way down and more areas need to be reforested than deforested – a tall order since data indicate forest loss continues to rise globally. However the authors offer a bit of hope, adding that “reforestation and protecting large forest areas nevertheless have potential to mitigate the consequences of fragmentation.”
Taubert, F., Fischer, R., Groeneveld, J., Lehmann, S., Müller, M. S., Rödig, E., … & Huth, A. (2018). Global patterns of tropical forest fragmentation. Nature.
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