The Amazon rainforest is responsible for absorbing around 25% of the carbon that is removed from the atmosphere by forests worldwide. There are concerns that deforestation is driving this region to a tipping point – in which abundant rainforests would transform into dry savanna. However, new research is emerging that suggests that the Amazon rainforest has a naturally-occurring border that gives it staying power.
Satellite data that shows savanna and rainforest side-by-side suggests that these regions have bistability, or alternative stable states. This means that events such as fires and drought could tip a large part of the rainforest into a state of savannah, where it would be locked until balance was restored.
Bert Wuyts, a fourth-year PhD student at the University of Bristol, set out to see if this theory was accurate.
“I decided to take a fresh look at the data and a very different picture emerged when I controlled for seasonality and took out all the data points from satellite images that represented locations that had been subjected to human influence. Suddenly the property of bistability disappeared almost completely,” explained Wuyts.
Wuyts made this discovery in the first year of his PhD. He teamed up with University of Bristol professor Alan Champneys, a theorist in the department of Engineering Mathematics and an expert on land use change from the School of Geographical Sciences.
The team analyzed the data for two years, and were able to identify key determining factors in the forest-savanna boundary that previous studies have overlooked. According to the reaction-diffusion theory, which is widely used to predict spatial interaction, there should be a distinct boundary between forest and savanna. This means that forest and savanna are equally stable.
Another determining factor is the proximity of the region to human activities. Logging and fire-induced erosion shift forest-savanna borders toward wetter conditions, which are more favorable for rainforests.
The findings of this study establish that deforestation does not have the power to push exposed areas of the Amazon rainforest to a tipping point. These regions should be able to bounce back after human activities are ceased.
On the other hand, a significant decrease in rainfall may result from having fewer trees in the rainforest. The researchers did not factor in the potential outcome of less rain, and further research is needed to explore this issue.
By Chrissy Sexton, Earth.com Staff Writer
Source: University of Bristol