New study refutes habitat fragmentation claim

The findings, published in "Nature", strike at the heart of a decades-long debate: Ecologists agree that habitat loss and the fragmentation of forests reduce biodiversity in the remaining fragments. However, ecologists disagree on whether it is better to focus on preserving many smaller, fragmented tracts of land or larger, continuous landscapes. 

"We find that habitat patches distributed across fragmented landscapes have fewer species in total than in more continuous landscapes", says Professor Jon Chase, co-author, iDiv group leader, and MLU professor. "Not just at the small scale, but also when patches across the whole landscape are combined. It’s this latter question, about what’s happening at the landscape scale, that has been the big topic of debate in recent years. We have provided clear evidence from many different forested landscapes that fragmentation is indeed bad for biodiversity, from smaller to larger scales."

Rigorously testing a controversial view
The study examined 4,006 species of vertebrates, invertebrates, and plants sampled at 37 sites around the world to provide a global synthesis comparing biodiversity differences between continuous and fragmented landscapes. They found that, on average, fragmented landscapes had 13.6 per cent fewer species at the patch scale and 12.1per cent fewer species at the landscape scale. 

Additionally, the findings suggest that primarily generalist species-species that are good at surviving in various environments-live in fragmented areas. 

The scientists investigated what is called alpha, beta and gamma diversity at these sites. Alpha diversity refers to the number of species in a patch, while beta diversity refers to how species composition - the variety and abundance of species within a particular area or ecosystem - differs between two areas. Gamma diversity refers to biodiversity over a whole landscape.

"The heart of the debate is that people who argue that fragmentation isn’t so bad say that because you have isolated habitats, you have different species composition, which means at a large scale, it’s good: if they are different, we can assume that the gamma diversity is going to be higher," says Thiago Gonçalves-Souza, first author and research scientist at U-M. "They say the opposite for large tracts of land: because this is a continuous and homogeneous patch, the species composition is too similar."

However, previous research didn’t properly compare fragmented landscapes to large, continuous forests, Gonçalves-Souza explains. For example, prior research may have looked at only one component of diversity or may have compared a few continuous forests to dozens of fragmented patches.

Instead, the ecologists constructed an analysis that corrected for differences in sampling across different landscapes. The group discovered that fragmentation decreased the number of species across all taxonomic groups but that the increase in beta diversity in fragmented landscapes did not compensate for species diversity loss at the landscape level.

What does this mean for minimising biodiversity loss?
Gonçalves-Souza hopes the study can move the conservation community past the debate over continuous versus fragmented landscapes and focus on the restoration of forests.

"I don’t know if it’s useful to think about continuous versus fragmented landscapes. We need to protect biodiversity and I think this debate is not helping to actually support conservation," he says. "In many, many countries, there aren’t many large, intact forests remaining. Therefore, our focus should be on planting new forests and restoring increasingly degraded habitats. Restoration is crucial for the future, more so than debating whether it’s better to have one large forest or many smaller fragments."

Study: Gonçalves-Souza T. et al. Species turnover does not rescue biodiversity in fragmented landscapes. Nature (2025). doi: 10.1038/s41586-025-08688-7

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