The Congo rainforest in Africa, the second-largest on our globe, is less green these days with a significant increase in browning in the last 10 years, researchers say.
An extended period of dry conditions in central Africa's Congo River basin is affecting the region's trees.
Their findings, published in Nature, are the result of a comprehensive study of the impact of long-term drought in the region's rainforest utilizing extensive satellite data.
If it continues, there could be significant alterations of the composition and structure of a rainforest second in size only to the Amazon, the researchers say.
"It's important to understand these changes because most climate models predict tropical forests may be under stress due to increasing severe water shortages in a warmer and drier 21st century climate," says study leader Liming Zhou at the University of Albany campus of the State University of New York.
The changes could turn the Congo basin from classic rainforest to an open savannah environment, affecting the region's biodiversity and its carbon storage capacity.
Field studies will be necessary to check if changes suggested by the satellite data are indeed occurring, including whether or not some trees are in fact dying from drought, something satellite data cannot confirm.
"Forests of the Congo Basin are known to be resilient to moderate climate change because they have been exposed to dry conditions in the past few hundred years," says study co-author Sassan Saatchi of NASA's Jet Propulsion Laboratory in Pasadena, California. "However, the recent climate anomalies as a result of climate change and warming of the Atlantic Ocean have created severe droughts in the tropics, causing major impacts on forests."
Another question to be answered is what changes might be experienced by particular plant species native to the rainforest region.
As an example, ongoing dry conditions might swing the climate in favor of one kind of tree over another.
"Trees are not as vigorous without enough water," Zhou says, explaining that drought conditions would favor deciduous trees rather than broadleaf evergreens, normally the majority of trees in a tropical rainforest.
"Our assessment is a step toward an improved understanding of how African rainforests respond to increasing drought," Zhou says. "We need to consider the complex range of processes affecting different tropical rainforest species before we can fully assess the future resilience of tropical forests."
