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African rainforests are surprisingly resilient to heat and drought

Scientists at the University of Leeds have tracked trees in 100 different tropical rainforests across six African countries. The study revealed that African rainforests continued to remove carbon from the atmosphere despite the extreme heat and drought of the last major El Niño event.

In 2015 and 2016, African rainforests experienced the strongest drought on record, driven by both El Niño conditions and climate change.

The researchers were surprised to find that the forests still managed to take up 1.1 billion tons of carbon dioxide per year during the El Niño monitoring period. To put this in perspective, this rate is equivalent to three times the carbon dioxide emissions of the UK in 2019.

“We saw no sharp slowdown of tree growth, nor a big rise in tree deaths, as a result of the extreme climatic conditions,” said study lead author Dr. Amy Bennett.

“Overall, the uptake of carbon dioxide by these intact rainforests reduced by 36%, but they continued to function as a carbon sink, slowing the rate of climate change.”

The study showed that the biggest trees in the forest were largely unaffected, while smaller trees grew less and died more during El Niño. Despite the negative effects, African rainforests continued to function as a carbon sink. The impacts on smaller trees were not enough to offset the long-term increase in overall tree biomass that has been observed in the forests over the last three decades.

“These findings show the value of careful long-term monitoring of tropical forests,” said study senior author Professor Simon Lewis. “The baseline data running back to the 1980s allowed us to evaluate how well these rainforests coped with record heat and drought.”

Rainforests in Asia and the Amazon did not respond as well to the drought and heat of past extreme weather events. These regions experienced substantially slower tree growth and much greater tree mortality, and the conditions led to a temporary reversal of the tropical forest carbon sink.

“Our results highlight just how important it is to protect African rainforests – they are providing valuable services to us all,” said study co-author Professor Bonaventure Sonké. “The resistance of intact African tropical forests to a bit more heat and drought than they have experienced in the past is welcome news. But we still need to cut carbon dioxide emissions fast, as our forests will probably only resist limited further rises in air temperature.”

Dr. Bennett noted that African tropical forests play an important role in the global carbon cycle, absorbing 1.7 billion tons of carbon dioxide from the atmosphere each year in the 2000s.

“To discover that they will be able to tolerate the predicted conditions of the near future is an unusual source of optimism in climate change science,” said Dr. Bennett.

“Our results provide a further incentive to keep global temperature increases to 1.5 degrees Celsius, as outlined in the Paris Agreement, as these forests look to be able to withstand limited increases in temperature and drought.”

The study is published in the Proceedings of the National Academy of Sciences.

By Chrissy Sexton, Staff Writer

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