New research will help shed light on role of Amazon forests in global carbon cycle

Julie Chao at the Berkeley Lab News Center: The Earth’s forests perform a well-known service to the planet, absorbing a great deal of the carbon dioxide pollution emitted into the atmosphere from human activities. But when trees are killed by natural disturbances, such as fire, drought or wind, their decay also releases carbon back into the atmosphere, making it critical to quantify tree mortality in order to understand the role of forests in the global climate system. Tropical old-growth forests may play a large role in this absorption service, yet tree mortality patterns for these forests are not well understood.

Now scientist Jeffrey Chambers and colleagues at the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) have devised an analytical method that combines satellite images, simulation modeling and painstaking fieldwork to help researchers detect forest mortality patterns and trends. This new tool will enhance understanding of the role of forests in carbon sequestration and the impact of climate change on such disturbances.

“One quarter of CO2 emissions are going to terrestrial ecosystems, but the details of those processes and how they will respond to a changing climate are inadequately understood, particularly for tropical forests,” Chambers said. “It’s important we get a better understanding of the terrestrial sink because if it weakens, more of our emissions will end up in the atmosphere, increasing the rate of climate warming. To develop a better estimate of the contribution of forests, we need to have a better understanding of forest tree mortality.”

...If these results hold for most tropical forests, then it would indicate that because we missed some of the mortality, then the contribution of these forests to the net sink might be less than previous studies have suggested,” Chambers said. “An old-growth forest has a mosaic of patches all doing different things. So if you want to understand the average behavior of that system you need to sample at a much larger spatial scale over larger time intervals than was previously appreciated. You don’t see this mosaic if you walk through the forest or study only one patch. You really need to look at the forest at the landscape scale.”...

A mortality map of the Amazon near Manaus, Brazil based on Landsat satellite images shows the spatial pattern of tree mortality. A Landsat image from NASA, found on the LBL National Lab website