Amazon in the firetrap
A new study published in Nature Communications Earth and Environment shows that fire can be a decisive factor for a potential tipping of the Amazon rainforest, as it is capable of locking large parts of the Amazon in a treeless state. While not naturally occurring in rainforests, fire can play an increasing role once the forest is damaged, thinned or completely lost, up to a status where fire is the dominating driver of the ecosystem.
“It turns out that fire is the important factor for locking the Amazon in a grassland state, preventing 56 to 86 per cent of the Amazon from regrowing, depending on the strength of climate change,” lead author Markus Drüke from the PIK explains. “We know that reversing Amazon forest loss becomes increasingly harder the more forest is lost, and our study shows that fire puts another lever onto this coherence."
Usually, the trees of the Amazon transport enormous amounts of water back to the atmosphere, which they originally received as rain. This water can form new rain locally or downwind in a process called moisture recycling, basically forming “flying rivers”, not only stabilising the Amazon as whole but also enabling it to extend into regions which would be too dry without this process.
This coherence is the main reason why the Amazon is considered a tipping element of the Earth system. Global warming and deforestation can damage these flying rivers leading to a self-reinforcing feedback of forest loss. The new study now underlines how fire dynamics help to push and lock the Amazon towards and in a savannah-like or treeless state.
Fire plays key role in irreversible transition
In contrast, in simulations without fire, the forest was able to recover over a longer period of within 250 years, which emphasises the important role of fire for the irreversibility of tropical deforestation.
“For the first time, it has been possible to calculate the feedbacks between fire, rainforest and climate in a process-based manner using the Earth system model POEM (Potsdam Earth Model),” adds co-author Kirsten Thonicke, Deputy Head of the Research Department on Earth System Analysis and Working Group Leader on Ecosystems in Transition at PIK. “Our results highlight the need to keep the Earth system within stable boundaries and limit climate change as well as tropical deforestation in order to prevent the tropical forest from crossing an irreversible fire-controlled tipping point,” Thonicke concludes.
Markus Drüke, Boris Sakschewski, Werner von Bloh, Maik Billing, Wolfgang Lucht, Kirsten Thonicke (2023): Fire may prevent future Amazon forest recovery after large-scale deforestation. Nature Communications Earth and Environment. [DOI: 10.1038/s43247-023-00911-5]