Researcher Takes Core from Tree (IMAGE) University of Arizona Caption Winston Wheeler, a researcher at the University of Arizona, collecting tree cores from a partially submerged tropical tree at Lake Bosumtwi, Ghana. A submerged forest in the lake provides evidence for severe and long-lasting droughts in West Africa just a few centuries ago. This tree grew at a time of prolonged drought when the lake level was tens of meters lower than today. Tree rings in the core sample were used to date the age of the tree and provide an additional line of evidence about megadroughts in the past. Credit Jonathan T. Overpeck. Usage Restrictions The photo may be used only to illustrate a story about the research described in this news release. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.