A section of the Amazon rainforest has flipped from a carbon sink to a major polluter after decades of human activity made it vulnerable to drought and wildfires, new research has found.

An eight-year study in Brazil’s Lower Tapajos in eastern Amazonia found the smaller, younger trees in re-growing – “secondary” – forest and in areas being selectively logged were much more vulnerable to extreme weather.

It found that in the wake of the strong El Nino event of 2015 to 2016, more than 2.5 billion small trees were killed in the region through a combination of drought and fire.

The research, led by scientists from the University of Lancaster and Oxford and the Brazilian Agricultural Research Corporation, found that in the three years after the El Nino, the Lower Tapajos region emitted 494 million tonnes of carbon dioxide.

The figure is higher than the UK’s annual CO2 emissions, which were 454.8 million in 2019, according to Government data.

Data was gathered regularly from 21 plots between 2010 to 2018 from a mixture of old-growth forests, recovering forests and forests that have been selectively logged.

It revealed that while the drought and subsequent fires triggered by the last El Nino killed many trees in virgin forests, the losses were much greater in recovering and other human-disturbed areas.

This was due to the fact the newer forest growth has much lower wood density and thinner bark, making it much more vulnerable to extreme weather and fire than mature trees.

The study found around 447 million large trees – larger than 10cm in diameter at a height of 1.37m above the forest floor – died across the Lower Tapajos following the 2015-2016 El Nino, compared to 2.5 billion smaller trees.

It further found trees and plants in areas of forest hardest hit by drought and fire continue to die at above normal rates for up to three years after the event, releasing even more CO2 into the atmosphere.

The researchers warned the findings could have significant implications for international efforts to limit global warming to between 1.5C and 2C above pre-industrial levels, as set out in the Paris Agreement.

Dr Erika Berenguer, lead author of the report from Lancaster University and the University of Oxford, said: “Our results highlight the enormously damaging and long-lasting effects fires can cause in Amazonian forests, an ecosystem that did not co-evolve with fires as a regular pressure.”

The research team said the findings highlight the urgent need to reduce illegal logging and other damaging activities in the Amazon.

They added greater investment in fire-fighting capabilities in the region was also vital.

Professor Jos Barlow of Lancaster University and the Universidade Federal de Lavras, one of the scientists leading the study, said: “The results highlight the need for action across different scales.

“Internationally, we need action to tackle climate change, which is making extreme droughts and fires more likely.

“At the local level, forests will suffer fewer negative consequences from fires if they are protected from degradation.”

The paper “Tracking the impacts of El Nino drought and fire in human-modified Amazonian forests” is published in the journal Proceedings of the National Academy of Sciences.

There is a growing body of evidence indicating that the Amazon could flip from being a vital carbon sink to a net emitter in a matter of decades as global temperatures rise.

Research published in the journal Nature last week that was conducted between 2010 and 2018 found south-eastern Amazonia in particular acts as a carbon source – partly driven by forest fires.

It found the region has been subject to greater deforestation, warming and drought than the western part, with the south-east experiencing the most extreme weather and greatest interference.

In the past 40 to 50 years, an estimated 17% of the Amazon rainforest has been lost.