A new University of Michigan-led study decisively finds that large, undisturbed forests better preserve biodiversity than fragmented landscapes, ending a long-standing ecological debate and underscoring the urgent need for forest restoration.
A landmark study led by the University of Michigan (U-M) has concluded that preserving large, undisturbed forests is far more effective for maintaining biodiversity than protecting fragmented landscapes. This study, published in Nature, addresses a crucial, decades-long debate among ecologists about the best strategies for conservation.
Ecologists have universally acknowledged that habitat loss and forest fragmentation lead to a reduction in biodiversity within the remaining patches. However, opinions have differed on whether it’s more beneficial to conserve numerous small, fragmented areas or larger, continuous landscapes.
The new research sheds light on this fundamental question.
“Fragmentation is bad,” co-author Nate Sanders, a U-M professor of ecology and evolutionary biology said in a news release. “This paper clearly shows that fragmentation has negative effects on biodiversity across scales. That doesn’t mean we shouldn’t try to conserve small fragments when we can with our limited conservation dollars, but we need to be wise about conservation decisions.”
The synthesis, led by U-M ecologist Thiago Gonçalves-Souza, examined 4,006 species of vertebrates, invertebrates and plants across 37 global sites, comparing biodiversity between continuous and fragmented landscapes.
The findings reveal that fragmented areas had 13.6% fewer species at the patch scale and 12.1% fewer species at the landscape scale, emphasizing the detrimental impact of fragmentation on biodiversity.
Key to the study were measurements of alpha, beta and gamma diversity — metrics that describe species richness within patches, differences in species composition among patches and overall landscape biodiversity, respectively.
Despite claims that species turnover in fragmented habitats might enhance landscape-level biodiversity (gamma diversity), the findings indicate otherwise.
“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,” added Gonçalves-Souza, a postdoctoral fellow at U-M’s Institute for Global Change Biology. “They say the opposite for large tracts of land: because this is a continuous and homogeneous patch, the species composition is too similar.”
The study’s authors, including researchers from Michigan State University and the German Centre for Integrative Biodiversity Research, utilized advanced data and statistical tools to compare biodiversity accurately across various landscapes.
This comprehensive approach revealed that the loss in species diversity due to fragmentation wasn’t offset by increased beta diversity.
“One reason that this has been such a long-standing and unresolved debate is that we simply have not had the appropriate data and statistical tools to systematically evaluate the question at both smaller and larger scales,” added co-author Jonathan Chase, a professor at the German Centre for Integrative Biodiversity Research.
“This paper resolves a half-century old debate about how to conserve biodiversity in natural areas, one started by scientific luminaries including E.O. Wilson and Jared Diamond,” co-author Nick Haddad, a researcher at Michigan State University, added.
Beyond biodiversity, fragmented landscapes potentially compromise the landscape’s capacity to store carbon, a critical factor in climate change mitigation.
“People are also comparing these two situations and finding that we are losing the ability for landscapes to store more carbon in fragmented landscapes,” added Gonçalves-Souza. “Fragmented landscapes are not only going to affect biodiversity by decreasing alpha and gamma diversity, but it also has implications for carbon stock as well.”
Looking forward, Gonçalves-Souza hopes the study will shift the focus of the conservation community from the debate over landscape types to active restoration efforts.
“I don’t know if it’s useful to think about continuous vs. fragmented landscapes. We need to protect biodiversity and I think this debate is not helping to actually support conservation,” Gonçalves-Souza added. “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.”
The global collaboration underscores the importance of holistic approaches to environmental conservation, guided by robust scientific data, to safeguard biodiversity and ecological health effectively.
Source: University of Michigan