Near-Complete Mammal Extinctions Occur in Fragmented Forests

Deforestation can be devastating for ecosystems. Even when steps are taken to preserve patches of forest, the fragmentation can wreak havoc on populations of animals that live there. Now, scientists have discovered that these small, fragmented forests can actually hasten the extinction of the mammals dwelling there, revealing how important it is to keep large stretches of forest intact.

In order to examine how fragmentation might impact species, the researchers journeyed to the Chiew Larn Reservoir in Thailand. They used the area as a natural laboratory, since the region was flooded from 1986 to 1987 to create more than 100 islands of tropical forests. This created the perfect type of fragmentation that the scientists wanted to study.

During their time at the site, the researchers performed surveys of the small mammals living in 16 of these fragmented patches of forest five to seven years after the floodwaters formed the islands. They then followed up this survey with another one 25 to 26 years afterward.

So what did they find? It turns out that within about five years, almost all small, native mammals had gone extinct in patches of forest that were less than 10 hectares. In addition, they found that small mammals had disappeared from larger 10- to 56-hectare forest fragments within 25 years.

"Our study focused on small mammals but what we did not report was a similar near-complete extinction of medium to large-sized mammals, such as elephants, tigers and tapirs, which are now completely absent from these islands in the reservoir," said Luke Gibson, co-author of the new study, in an interview with BBC News. "All of these animals were in the forest landscape before the creation of the reservoir."

The findings have serious implications for fragmented forests. Not only do they show the devastation that can be caused, they also show that species may be in real danger as humans continue to encroach on their habitat.

"It was like ecological Armageddon," said Gibson in an interview with Phys.org. "Nobody imagined we'd see such catastrophic local extinctions. The bottom line is that we must conserve large, intact habitats for nature. That's the only way we can ensure biodiversity will survive."

The findings are published in the journal Science.