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Conserving biodiversity requires large forest areas and continuous landscapes
An article published in Nature compared biodiversity across different landscapes and revealed a decline in species within small forest fragments
Process of habitat fragmentation can be observed in the advance of the agricultural frontier in the Pantanal and the Amazon region – Image: Reproduction / Researcher’s archive
Should we preserve several small habitat fragments or a few large ones? Known by the acronym SLOSS, from the English Single Large or Several Small, the conservation debate was the subject of a publication in the journal Nature, which sought to provide a global synthesis of the discussion. Using data from 4,006 species of vertebrates, invertebrates, and plants across 37 locations around the world, the study compared differences in biodiversity between continuous and fragmented landscapes.
The study included the participation of Thiago Gonçalves-Souza, from the University of Michigan, as well as researchers from 27 institutions in the United States, Brazil, Germany, the United Kingdom, Argentina, Australia, Switzerland, and Mexico, including USP.
For comparison purposes, the study investigated the alpha (α), beta (β), and gamma (γ) diversity of these locations. Alpha refers to the number of species within a habitat patch, while beta refers to how species composition changes between two habitat areas; and gamma refers to the biodiversity across an entire landscape. On average, fragmented landscapes had 13.6% fewer species at the fragment scale and 12.1% fewer species at the landscape scale. Fragmentation reduced the number of species across all taxonomic groups, and the increase in diversity between two areas did not offset the loss of diversity at the landscape scale.
“The results show that we need to have the largest forests possible and imaginable”
Thiago Gonçalves-Souza - Photo: Personal archive
In an interview with Jornal da USP, Gonçalves-Souza states that habitat loss and fragmentation often lead to a decline in the number of species locally, but his interest was in how the effects of fragmentation change at the landscape scale. The supposed rescue of γ (gamma) diversity through the increase of β (beta) diversity was carefully tested and contested, which prioritized continuous landscapes and large forests for conservation. Nevertheless, the researcher argues “when we don’t have fragments, it is worse than having small ones. Small fragments are very important. But in order to conserve biodiversity, if you have a larger area, please protect it.”
Methodological challenges
To analyze the differences between alpha, beta, and gamma diversities, the researcher initially used a database called FragSat, which contains data on forest fragments worldwide where researchers collected data on different organisms to understand how they respond to forest loss. However, there was a limitation regarding the information on what surrounded the forest. More than 90 researchers were contacted individually by Gonçalves-Souza to create LandFrag, a database compiled by the researcher that solved the previous problem. In total, 121 studies were compiled.
Out of these 121, he compiled 37 studies that compared large forest fragments with small fragments in a sub-database created to meet the research demands. “So, we arrived at a fundamental subset, decided together with the main experts, which required the participation of all those who provided the data, because without this data, it wouldn’t exist,” says the researcher. After collecting all this information, the researcher formatted the data for questions that had not been asked by the initial researchers and were of his interest in this study.
Despite the consensus on the negative effects of habitat loss, the effects of fragmentation were uncertain - Image: Reproduction / Researcher's Archive
Despite the logistical challenges of contacting each researcher, the methodology also needed to be aligned due to the diversity of the data collected. One of the first problems presented was the sampling effort when comparing larger and smaller regions; that is, collections at different points in smaller regions require more “effort” than in larger regions, where the sampling points are farther apart from each other. A rarefaction – a statistical resampling method – was performed to allow for comparison.
Another complication was a concern with the fidelity of the β (beta) diversity numbers due to the spatial issue. Another complication was a concern with the fidelity of the β (beta) diversity numbers due to the spatial issue. He gives the example of the distance between Ibirapuera and the Cidade Universitária Armando de Salles Oliveira, in Butantã, and then to the next fragment. “I only made the calculation for fragments that were next to each other, instead of including fragments that were very far apart,” he explains.
Another variable taken into account was the age of fragmentation and its effects on alpha, beta, and gamma diversities. Since many fragments had little documentation about their degradation, they were categorized as deforested in the last 40 years or more than 100 years ago. The observed result was the same for both categories: large or continuous areas have more species than smaller fragmented areas. Although it seems like a logical conclusion, it goes against a logic that views fragmentation in a more positive light.
Edge effect and generalist species
“The idea is that when a forest is fragmented, new habitats are created with different qualities and species compositions. With different fragments housing different species, even in small numbers, the landscape as a whole would gain in diversity,” informs Gonçalves-Souza. Despite this perspective, the study proves the lack of gain in landscape diversity.
Adriano Chiarello, co-author of the study and professor at the Department of Biology at the Faculty of Philosophy, Sciences, and Letters of Ribeirão Preto (FFCLRP) at USP, also points to the rapid degradation of the quality of fragmented habitats due to the “edge effect.'” This consists of the increased exposure to wind, temperature, dryness, invasion of exotic species, among other factors that could worsen with climate change.
“The 26 mammal species that remained in the northeastern part of São Paulo are generalists. The specialists have already been extinct, as they depend either on more specialized environments or on large forest masses.”
Adriano Chiarello - Photo: Personal archive
Although returning to original ecosystems is not a viable proposal, he draws attention to the Brazilian Forest Code (Law No. 12.651/2012). Article 12 of the code defines the need to maintain the Legal Reserve within rural properties with the minimum percentages of native vegetation that must be preserved. Article 3, item II, defines the Permanent Preservation Areas (APPs, in the Portuguese acronym), which must also be protected even within private properties, such as riverbanks, slopes, and hilltops.
These mechanisms aim to create functional connections between fragments for biodiversity preservation. With the advance of the agricultural frontier over the dense Amazon rainforest and the devastation pointed out in Atlantic Forest regions, the role of these legal instruments is crucial to protect critical areas, as “the more complex the forest massif, the more drastic the effect of fragmentation,” warns Chiarello.
The paper Species turnover does not rescue biodiversity in fragmented landscapes is available here.
More information: tgoncalv@umich.edu, with Thiago Gonçalves-Souza
*Intern under the guidance of Tabita Said
Política de uso
A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.
A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.