Douglas-fir Cross-section Shows Annual Tree Rings (image) University of Arizona Share Print E-Mail Caption Annual tree rings record a detailed history of drought (narrow rings) and wetness (wide rings). This sample from a dead Douglas-fir tree in the Santa Catalina Mountains near Tucson, Ariz., has nearly 400 rings and dates back to the year 1600. Stress cracks, visible in the foreground of the image, occur as the dead wood dries and contracts. Credit Copyright Daniel Griffin. Usage Restrictions This photo may be used only to illustrate a story about the research described in the accompanying release, Hot with Decades of Drought: Expectations for the Southwest. Share Print E-Mail 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.