A recent study has revealed that Brazilian forests in areas facing significant deforestation and degradation are increasingly dominated by fast-growing, small-seeded tree species.
This shift may impact the ecosystem services provided by these forests, particularly their ability to capture and store carbon. These ‘winning’ species thrive quickly but have shorter lifespans, resulting in less dense stems and branches compared to the slower-growing tree species they replace.
Additively, wildlife that relies on larger seeds from certain tree species—now dwindling in human-altered landscapes—might also be impacted by this ecological transition.
The study, published today in Nature Ecology and Evolution, emphasizes the critical need for conservation and restoration of tropical forests. It also highlights the importance of safeguarding and enhancing populations of large-fruited birds, like toucans, and mammals such as spider monkeys that are vital for the dispersion of the larger-seeded, slow-growing tree species that are at risk.
An international research team analyzed an extensive dataset comprising over 1,200 tropical tree species gathered from more than 270 forest plots in six regions of the Brazilian Amazon and Atlantic forests, which have been altered through human activities such as logging, hunting, and burning.
The researchers examined the overall structure of the landscapes around each forest plot. By applying various statistical models, they identified the causal relationships between habitat loss, fragmentation, and local disturbances on forest composition, distinguishing between the traits of the so-called “winners” and “losers.”
Bruno X. Pinho, the study’s lead author and former researcher at the University of Montpellier (currently at the University of Bern), stated, “Our findings reveal that tree species prevalent in areas with substantial forest cover usually have dense wood and large seeds, which are mainly spread by medium to large animals found in Brazil’s rainforests. Conversely, in regions with heavy deforestation, these species are being replaced by ‘opportunistic’ species that have softer wood and smaller seeds, favored by small, mobile birds and bats that thrive in disturbed areas. These species tend to grow faster and disperse more widely.”
This phenomenon was observed across different geographical, climatic, and land-use conditions.
The study underscores the urgent necessity for enhancing conservation and restoration efforts in tropical forests to protect these crucial ecosystems.
Professor Jos Barlow, a senior investigator from Lancaster University, remarked, “The significant impact of forest degradation in certain Amazon regions highlights the necessity for strategies that go beyond merely addressing deforestation to also encompass measures against forest disturbances like selective logging and fires.”
Tropical forests are essential reservoirs of terrestrial biodiversity, playing a critical role in greenhouse gas absorption and providing invaluable ecosystem services. However, they continue to suffer from rapid deforestation and habitat fragmentation, with an estimated loss of 3 to 6 million hectares annually over the past twenty years. Consequently, a significant portion of today’s tropical forests exist within human-modified landscapes and are subject to local disturbances.
Felipe Melo, the study’s second author and a researcher at the Federal University of Pernambuco in Brazil (currently at Nottingham Trent University), explained, “These functional replacements could have serious implications that ought to be promptly assessed, as they may trigger declines in vital ecosystem processes and their contributions to human communities—especially regarding changes in carbon reserves, as well as interactions between fauna and flora, and forest regeneration.”
David Bauman from the French National Research Institute for Sustainable Development (IRD) and a co-author of the study, added, “While there is widespread agreement on the detrimental effects of habitat loss on biodiversity, the isolated impacts of landscape fragmentation and local disturbances are still not well understood. This is largely due to the complications of differentiating causal relationships from non-causal ones.”
The research also addresses these critical questions, demonstrating that policies ought to prioritize the preservation and improvement of forest cover while focusing less on the distribution of remaining forests across landscapes.
Funded by the UKRI National Environment Research Council, the findings of this study are detailed in the paper titled ‘Winner-loser plant trait replacements in human-modified tropical forests,’ published in Nature Ecology and Evolution.
