The Amazon is reaching the tipping point whereby it will switch from rainforest to a savannah, researchers have warned.
Sensitivity to rainfall and moisture changes, as well as fires and lengthy droughts, can lead to areas of rainforest losing trees, moving towards a sparser mixture of woodland and grassland rather than the dense, closed canopy areas we associate with the world’s rainforests.
Experts have long understood that these sorts of changes would be possible in the Amazon rainforest, however it was previously assumed we wouldn’t see such a drastic shift for decades to come.
Now, new research published in the journal Nature Communications suggests we could well be closer to a tipping point than had previously been anticipated.
This study found that much as 40% of the Amazon has now reached a point where it could become a savannah rather than a rainforest, with climate change meaning some parts are receiving significantly less rainfall than they once did.
The findings from the study, by the Stockholm Resilience Centre, were based on computer models and data analysis, with researchers using ‘remote sensing, a global hydrological model, and detailed atmospheric moisture tracking simulations’.
According to the study authors:
The Amazon forest could partially recover from complete deforestation, but may lose that resilience later this century.
The Congo forest currently lacks resilience, but is predicted to gain it under climate change, whereas forests in Australasia are resilient under both current and future climates.
With the right climate, rainforests can effectively produce their own self-sustaining rainfall, however their ecology means they are susceptible to drying out under the wrong conditions.
Lead study author, Arie Staal, told The Guardian:
As forests grow and spread across a region, this affects rainfall. Forests create their own rain because leaves give off water vapour and this falls as rain further downwind. Rainfall means fewer fires leading to even more forests.
Rainfall levels within a region have been shown to decline if large areas of rainforest are destroyed, leading to reduced levels of ‘atmospheric moisture recycling’. These levels were simulated in the computer models used for this study.
Drier conditions make it harder for the forest to recover and increase the flammability of the ecosystem.
It is harder to return from the ‘trap’ caused by the feedback mechanism in which the open, grassy ecosystem is more flammable, and the fires, in turn, keep the ecosystem open.
Another recent study, published in Science, found that long-term forest degradation has now surpassed deforestation in the Amazon, on account of increases in logging activities and understory burning.
As well as having worrying implications for carbon, biodiversity and energy balance, experts have warned than degradation could lead to new diseases emerging, with the Amazon potentially being the source of the next pandemic.
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