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

[Press release] - Published on December 10, 2024 in Press Room, Science-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 tropical forest degradation. This study, published in the journal Nature Ecology & Evolution on December 10, highlighted "winning" and "losing" species, leading to the functional impoverishment of tropical forest ecosystems.

Dominance of "opportunistic" species

This study highlights a decline in functional diversity caused by deforestation and habitat degradation, widespread 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 changes 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 grow rapidly with low wood density, high fertility, and a high dispersal capacity with small seeds consumed by small mobile vertebrates such as birds or bats," explains Bruno X. Pinho, lead author of the study and postdoctoral researcher at the University of Montpellier within the AMAP research unit (now at the University of Bern). On the other hand, the authors find that other characteristics of species 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 replacements have serious implications that urgently need to be quantified. They suggest possible deterioration of essential processes in these ecosystems and their contributions to human populations, particularly through changes in biogeochemical cycles—especially carbon—but also in fauna-flora interactions and forest regeneration," explains Felipe Melo, second author of the study and researcher at the Federal University of Pernambuco in Brazil (now at Nottingham Trent University). This study thus highlights the urgent need to strengthen the conservation and restoration of tropical forests in order to preserve these vital ecosystems. "The strong influence 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. However, they are suffering from rapid deforestation and fragmentation, with a loss of 3 to 6 million hectares per year over the last two decades. Much of today's tropical forests are therefore located in landscapes that have been altered by humans and are exposed to local disturbances such as logging, hunting, and fires.

"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 of disentangling cause-and-effect relationships from non-causal associations," explains David Bauman, IRD researcher at the AMAP laboratory and co-author of the study. Some studies report a positive effect of this fragmentation, but others report a negative effect. These effects, which are often weak, are documented exclusively in terms of species numbers. However, a small impact on the number of species may 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 to guiding the management of fragmented landscapes in a way that preserves these ecosystems and their diversity," David emphasizes.

The study is based on a unique dataset, incorporating inventories of 271 forest plots distributed across six anthropized regions of the Amazon and Brazilian Atlantic forests, characterizations of the landscape configuration in these regions, and the morphological and functional characteristics of the wood, leaves, and seeds of 1,207 tropical tree species. Using statistical models, it was possible to break down 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 "winning" and "losing" species with convergent traits in different regional contexts.