Tree-rings Show 1600s Megadrought (image) University of Arizona Caption This Douglas-fir sample from the Southwest has annual tree rings dating back to the year 1527. The narrowing of the rings that formed from the 1560s through the 1590s indicates that the tree grew little during the 16th century megadrought. Credit Copyright Daniel Griffin. Usage Restrictions This image may only be used to illustrate a story about the research described in the release, Climate Change to Cripple Southwestern Forests. Photo credit must be given to Daniel Griffin. 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.