Amazonian forests altered by human actions show broad changes in diversity and evolutionary patterns

by Sophie Jenkins
London, UK (SPX) Nov 11, 2025

A comprehensive international study has found that human activity is driving deep changes in the Amazon rainforest, reshaping its ecological functions and evolutionary history. Researchers led by Lancaster University and the University of Oxford examined more than 55,000 trees across 215 plots in eastern Amazonia, representing a spectrum of disturbance - including primary forests, selectively logged sites, areas affected by fire, and secondary forests recovering from land clearance.

Their analysis assessed species diversity, functional types linked to ecological roles, and evolutionary lineages among trees. The team found that all forms of human disturbance, including logging and wildfires, reduced diversity at every level. The impact was so strong that it overwhelmed differences among diversity measurement methods, showing that disturbance itself is the key driver of change.

"While these advances are important, our results show that when it comes to understanding human influences on rainforests, it does not matter much - human influences are so profound that all measures are changing, and it is the disturbance itself that determines the degree of change," said Dr Erika Berenguer of Lancaster University and Oxford.

Secondary forests, which grow back after clear felling, exhibited particularly distinct ecological and evolutionary characteristics compared to undisturbed forests. These disturbed environments had fewer tree species, evolutionary lineages, and functional types - and their species composition shifted toward more pioneer species, with fewer slow-growing large trees.

"Disturbed primary forests and secondary forests had lower numbers of tree species, but also lower numbers of evolutionary lineages and functional types of trees. However, it wasn't just the numbers that were lower, but also the identity of the species, lineages and functional types changed after disturbance. Disturbance is not only resulting in impoverished tree diversity, it is changing the species composition of human-modified Amazonian forests. An example of this is we find disturbed forests see a greater prevalence of 'pioneer' tree species and much fewer of the larger slower growing species we find in undisturbed forests," stated Dr Cassio Alencar Nunes of Lancaster University and Universidade Federal de Lavras.

The team cautions that even so-called sustainable practices, such as selective logging, significantly reduce tree diversity and alter forest structure, threatening resilience and the provision of ecosystem services like carbon sequestration. Professor Jos Barlow of Lancaster University noted, "Our findings show that human-modified forests are fundamentally different from their undisturbed counterparts. As the Amazon faces mounting human pressures, conserving remaining undisturbed forests is essential - not only for their carbon-storing potential but also to preserve the deep evolutionary heritage that has shaped one of our planet's most diverse ecosystems."

The study also suggests that protecting disturbed forests may still offer ecological benefits over areas cleared entirely and left to regenerate, and highlights funding mechanisms such as the Tropical Forest Forever Facility (TFFF) to conserve all forest types.

Dr Berenguer emphasized, "Although the focus of COP30 is mostly on carbon, linking climate discussion with biodiversity is essential if we want to overcome the climate and biodiversity crisis. Ultimately, biodiversity is what guarantees the provision of ecosystem services such as carbon sequestering and stocking. Given that disturbed forests presented impoverished and distinct tree compositions, it is expected that large areas of the Amazon are already unable to provide the full range of ecosystem services found in undisturbed primary forests."

Research Report:Multi-faceted assessment of Amazonian tree diversity reveals pervasive impacts of human modifications