What are the consequences of deforestation and the degradation of tropical forests on ecosystems?

[Press Release] - Published on December 10, 2024 in Press Room, Science and Society

An international team composed of several researchers from the AMAP laboratory (Botany and Modeling of Plant and Vegetation Architecture) under the auspices of the University of Montpellier and INRAE investigated the consequences of deforestation and the degradation of tropical forests. This study, published in the journal Nature Ecology & Evolution on December 10, identified “winner” and “loser” species, leading to the functional impoverishment of tropical forest ecosystems.

Dominance of "opportunistic" species

This study highlights a decline in so-called functional diversity caused by deforestation and habitat degradation, a phenomenon observed across six major regions of the Amazon and Atlantic forests. The results show that landscape-scale habitat loss and local degradation of tropical forests lead to similar shifts in tree species across different biogeographic, climatic, and land-use contexts. “We find that these anthropogenic pressures lead to the dominance of so-called ‘opportunistic’ species, which typically exhibit rapid growth with low wood density, high fertility, and a high dispersal capacity via small seeds consumed by small, mobile vertebrates such as birds or bats,” explains Bruno X. Pinho, the study’s lead author and a postdoctoral researcher at the University of Montpellier within the UMR AMAP (now at the University of Bern). On the other hand, the authors find that other species characteristics underlie significant vulnerability to landscape fragmentation, such as the production of large seeds, whose dispersal depends on large animals and whose germination is physiologically constrained.

Risks to essential ecosystem services in the tropics

“These functional substitutions have serious implications that urgently need to be quantified. They suggest potential impairments to essential processes within these ecosystems and their contributions to human populations, particularly through changes in biogeochemical cycles—especially the carbon cycle—as well as in flora-fauna interactions and forest regeneration,” explains Felipe Melo, the study’s second author and a researcher at the Federal University of Pernambuco in Brazil (currently at Nottingham Trent University). This study thus underscores the urgency of strengthening the conservation and restoration of tropical forests to preserve these vital ecosystems. “The significant impact of forest degradation in certain Amazonian regions demonstrates the importance of combating forest disturbances, such as selective logging and fires, as well as deforestation,” emphasizes Professor Jos Barlow of Lancaster University.

Tropical forests are the most important reservoir of terrestrial biodiversity. They play a major role in global biogeochemical cycles and provide essential ecosystem services. Yet they are suffering from rapid deforestation and fragmentation, with 3 to 6 million hectares lost annually over the past two decades. As a result, a large portion of today’s tropical forests are located in landscapes altered by human activity and exposed to local disturbances such as logging, hunting, and wildfires.

“There is broad consensus on the negative impact of habitat loss on biodiversity, but the independent effects of landscape fragmentation and local disturbances are still poorly understood and hotly debated, particularly because of the difficulty in distinguishing between cause-and-effect relationships on the one hand and non-causal associations on the other,” explains David Bauman, an IRD research fellow at the AMAP laboratory and co-author of the study. Some studies report a positive effect of this fragmentation, while others report a negative one. These effects, often small, are documented exclusively in terms of species numbers. However, a small impact on species numbers can mask the replacement of several species by others with different ecological strategies, with significant consequences for the diversity and functioning of these ecosystems. “Understanding these changes and distinguishing causality from non-causal associations is crucial for guiding the management of fragmented landscapes in a way that preserves these ecosystems and their diversity,” emphasizes David.

The study is based on a unique dataset that includes inventories of 271 forest plots distributed across six anthropogenically altered regions of the Amazon and Brazilian Atlantic Forest, characterizations of landscape patterns in these regions, as well as the morphological and functional characteristics of the wood, leaves, and seeds of 1,207 tropical tree species. Using statistical models, it was possible to decompose the causal, direct, and indirect effects of habitat loss, fragmentation, and local degradation on the functional composition of forests. Finally, it was possible to identify so-called “winner” and “loser” species with convergent traits across different regional contexts.