According to research from the University of Michigan, extensive, untainted forests are superior for nurturing biodiversity compared to fragmented environments.
Ecologists concur that the loss of habitat and forest fragmentation diminishes biodiversity in the remaining patches. Nevertheless, there is contention among ecologists regarding whether to prioritize the preservation of numerous small, fragmented areas or larger, uninterrupted landscapes. The investigation, published in Nature and led by U-M ecologist Thiago Gonçalves-Souza, provides a resolution to this long-standing controversy.
“Fragmentation is detrimental,” stated study author Nate Sanders, a professor of ecology and evolutionary biology at U-M. “This research clearly demonstrates that fragmentation adversely impacts biodiversity across various scales. This doesn’t imply we should neglect conserving smaller fragments when we can, with our limited conservation resources, but we must make prudent conservation choices.”
The research, executed by scholars from U-M, Michigan State University, and the German Centre for Integrative Biodiversity Research, among others, evaluated 4,006 species of vertebrates, invertebrates, and plants collected from 37 locations worldwide. This provided a comprehensive analysis comparing biodiversity variations between continuous and fragmented environments. The findings revealed that, on average, fragmented areas showed a 13.6% reduction in species richness at the patch scale and 12.1% fewer species at the landscape scale.
Moreover, the results imply that generalist species—those adept at thriving in diverse habitats—are predominantly found in fragmented zones.
The researchers assessed what is termed alpha, beta, and gamma diversity at these locations. Alpha diversity refers to the quantity of species within a patch, while beta diversity pertains to the variations in species composition between two regions. Gamma diversity encompasses the overall biodiversity across a complete landscape.
Consider traversing Ohio’s agricultural fields and encountering patches of forest nestled between them, suggests Sanders. Each forest patch might have a limited number of bird species (alpha diversity), yet each patch will feature different bird species compared to the previous one (beta diversity). The overall biodiversity across the entire landscape containing these fragmented patches—or a continuous forest—is described as gamma diversity.
“The crux of the argument lies in the fact that proponents of fragmentation not being as harmful assert that isolated habitats lead to different species compositions, which in turn implies that at a broader scale, it’s beneficial. If variations exist, we can infer that gamma diversity will be higher,” said Gonçalves-Souza, a postdoctoral fellow at U-M’s Institute for Global Change Biology. “Conversely, they argue that large land parcels suffer because of their continuous and uniform nature, leading to excessively similar species compositions.”
However, prior studies didn’t adequately compare fragmented landscapes with extensive, continuous forests, Gonçalves-Souza remarked. For instance, earlier work might have examined only one aspect of diversity, or compared a small number of continuous forests with numerous fragmented patches.
“The reason for this prolonged and unresolved debate is the lack of suitable data and statistical methods to comprehensively analyze the issue across different scales,” explained co-author Jonathan Chase, a professor at the German Centre for Integrative Biodiversity Research.
Gonçalves-Souza and his colleagues devised an analysis that adjusted for variances in sampling across disparate landscapes. Their findings revealed that fragmentation diminished species numbers among all taxonomic categories, yet the rise in beta diversity within fragmented areas did not offset the loss of species diversity at the landscape level.
“This paper resolves a decades-long debate on how best to conserve biodiversity in natural environments, initiated by esteemed scientists like E.O. Wilson and Jared Diamond,” stated co-author Nick Haddad, a researcher at Michigan State University.
Gonçalves-Souza noted that biodiversity is not the only element compromised when landscapes fragment: the capacity of these landscapes to sequester carbon is also affected.
“Studying these two scenarios reveals a decline in landscapes’ capacity to store carbon in fragmented regions,” Gonçalves-Souza commented. “Fragmented landscapes not only diminish biodiversity by lowering alpha and gamma diversity but also have repercussions for carbon storage.”
Gonçalves-Souza aspires for this study to guide the conservation community away from the ongoing discourse surrounding continuous versus fragmented landscapes and redirect attention towards forest restoration efforts.
“I question the usefulness of contemplating continuous versus fragmented landscapes. Our priority should be safeguarding biodiversity, and I believe this debate hinders effective conservation efforts,” he stated. “In numerous countries, there are few intact, large forests left. Thus, our emphasis should be on creating new forests and rehabilitating increasingly degraded habitats. Restoration is vital for the future, more so than deliberating the merits of having one vast forest versus several smaller patches.”
This research stemmed from a global collaboration of ecologists, supported by the University of Michigan, according to Sanders, who also serves as the chair of the U-M Department of Ecology and Evolutionary Biology.