The forest is a gigantic carbon sink, drawing the greenhouse gas from the atmosphere. Cleared areas that are re-planted are known as secondary forest, and have been seen as key to fighting climate change, researchers at Lancaster University said.
But a new study has found that those areas held just 40 per cent as much carbon dioxide as sequestered by parts of the Amazon untouched by humans, casting doubt on their ability to aid in mitigating the crisis.
And at the same time, global warming appeared to be hampering the re-growth of secondary forest.
Scientists monitored forest regrowth over a period of 20 years and revealed how the Amazon was affected by periods of drought. During times of “water deficit”, regrown forests absorb less carbon from the atmosphere.
“If current trends continue, it will take well over a century for the forests to fully recover, meaning their ability to help fight climate change may have been vastly overestimated,” Lancaster University said.
Increased temperatures from global warming are in turn causing more drought-years in the Amazon, therefore limiting the capabilities of the secondary forests to help beat carbon pollution.
Led by a group of Brazilian and British researchers, the study also found that even after 60 years, regrown forests held only two-fifths as much carbon as virgin forests.
It could take more than a century for the forests to fully recover and “reduce the effectiveness of climate mitigation strategies in regions that have a long history of human occupation”.
Author Fernando Elias, of the Federal University of Para, said: “The region we studied in the Amazon has seen an increase in temperature of 0.1C per decade and tree growth was lower during periods of drought.
“With predictions of more drought in the future, we must be cautious about the ability of secondary forests to mitigate climate change. Our results underline the need for international agreements that minimise the impacts of climate change.”
Scientists also found there to be a “near-zero increase” in biodiversity within these secondary forests between 1999 and 2017.
Forests are vital habitats for threatened species and ecosystems, but results from the study show poor biodiversity relationships in highly-deforested landscapes.
“It is also likely that we are overestimating the relative recovery of biodiversity,” added the study.
Joe Barlow, professor of conservation science at Lancaster University and also an author of the study, said secondary forests’ potential to mitigate climate change was of “global importance”.
He also called for “more long-term studies like ours… to better understand secondary forest resilience and to target restoration to the areas that will do most to combat climate change and preserve biodiversity”.