• 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.

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