Human disturbance has caused a diversity crisis in the Amazon

When the world gathers at COP30, most conversations about the Amazon will orbit carbon – how much it stores, how much it can soak up. But a new study says we’re missing the bigger picture. 

Tropical forests are more than carbon sinks; they’re living archives of evolution and engines of ecological function.

In the Amazon forest, human disturbances are now changing which trees grow, how they work, and how deep their evolutionary roots run.

Triple view of tree diversity

An international team led by researchers at Lancaster University and the University of Oxford surveyed more than 55,000 trees across 215 plots in eastern Amazonia. 

The plots spanned untouched primary forest, selectively logged forest, forest hit by logging and wildfire, and secondary forest recovering after clear-felling.

For each site, the team measured three variants of diversity: the number of species, the functional roles those species play (traits like bark thickness, wood density, leaf area), and how those species are related on the tree of life.

This “triple view” matters. Species counts tell you how many players are on the field. Functional diversity tells you what roles they can cover. Phylogenetic diversity tells you how different their evolutionary lineages are. 

Profound human influences

The results of the analysis showed that any form of human disturbance, such as selective logging, wildfires, or clear-felling followed by regrowth pushed all three dimensions of diversity downward.

The effects were so pervasive they overwhelmed the nuances between different metrics.

Erika Berengue, a scientist at Lancaster and Oxford who co-led the study, said that human influences are so profound in forests that all measures are changing, and it is the disturbance itself that determines the degree of change.

In plain terms: it isn’t just that there are fewer species where people have cut or burned. The entire identity of those forests shifts.

Pioneer trees – fast-growing, disturbance-loving species – move in. The slow, towering giants that define intact rainforest structure become scarce. Functional variety narrows. Evolutionary breadth contracts.

Secondary forests aren’t substitutes

The most altered communities were in secondary forests – areas cleared outright and now regrowing. Clear-felling is the most severe disturbance. 

This distinction matters for policy. Much climate accounting treats secondary forests as interchangeable with primary ones. This work says they’re not. They look different, work differently, and descend from shallower evolutionary branches.

Cássio Alencar Nunes from Lancaster University and the Universidade Federal de Lavras in Brazil noted that 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,” said Nunes.

“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.”

Why this matters for resilience

Forests rich in species, functions, and deep evolutionary lineages tend to be more robust. They buffer droughts, resist pests, cycle nutrients, and store carbon more stably. Strip out that depth and breadth, and the system can become more brittle. 

The Amazon’s famed hyperdiversity – up to 16,000 tree species, with a single hectare often harboring 300 or more – has been a cornerstone of that resilience. Human disturbance is eroding it.

Selective logging is often framed as sustainable. This study suggests otherwise. Even low-intensity extraction leaves fingerprints across species composition, trait profiles, and evolutionary structure, which are the three pillars that underpin ecosystem services.

Human-modified forests are different

According to study co-author Jos Barlow, the 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,” said Barlow.

“However, our results also demonstrate the value of disturbed forests when compared to forest regeneration after clear felling.”

“This highlights the importance of novel protection mechanisms such as the Tropical Forest Forever Facility (TFFF) that provide a way of funding the conservation of all forests, and not just those that remain unimpacted by humans.”

Linking climate and biodiversity

Carbon targets alone won’t secure the Amazon’s future. Disturbance has already produced forests that are ecologically and evolutionarily distinct from their undisturbed neighbors, and less capable of delivering the full suite of services we rely on.

Berenguer noted that 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,” said Berenguer.

“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.”

Protecting the Amazon forest

This study provides clear steps to follow to resolve these issues. Protect what remained intact. Tighten controls on fire and logging in primary forests.

Treat secondary forests as valuable, but not equivalent, and invest in their ecological recovery beyond just tree cover.

Furthermore, build finance mechanisms that reward the full spectrum of forest functions – carbon, yes, but also evolutionary heritage and the functional diversity that keeps the Amazon alive.

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