A larger part of the Amazon rainforest than previously thought is at risk of crossing a tipping point where it could become a savanna-type ecosystem, according to new a new study.
The research, based on computer models and data analysis, is published by a team of scientists including Johan Rockström, Director of the Potsdam Institute for Climate Impact Research, in the journal Nature Communications. Rainforests are very sensitive to changes that affect rainfall for extended periods. If rainfall drops below a certain threshold, areas may shift into a savanna state.
“In around 40 percent of the Amazon, the rainfall is now at a level where the forest could exist in either state – rainforest or savanna, according to our findings,” says lead author Arie Staal, formerly a postdoctoral researcher at the Stockholm Resilience Centre and the Copernicus Institute of Utrecht University. “As tropical 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. As forests shrink, we get less rainfall downwind and this causes drying leading to more fire and forest loss: a vicious cycle, Our computer simulations capture this dynamic.”
The researchers explored the resilience of tropical rainforests in the Americas, Africa, Asia and Oceania by looking at two questions: what if all the forests in the tropics disappeared, where would they grow back? And its inverse: what happens if rainforests covered the entire tropical region of Earth? Such extreme scenarios could inform scientists about the resilience and stability of real tropical forests. They can also help us understand how forests will respond to the changing rainfall patterns as greenhouse gases in the atmosphere rise.
- Staal, Arie, Fetzer, Ingo, Wang-Erlandsson, Lan, Bosmans, Joyce H.C., Dekker, Stefan C., van Nes, Egbert H., Rockström, Johan & Tuinenburg, Obbe A. (2020): Hysteresis of tropical forests in the 21st century. Nature Communications [doi:10.1038/s41467-020-18728-7]
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