Douglas Fir Cross-Section (image) University of Arizona Caption This cross-section of a Douglas fir from Arizona shows the tree's annual growth rings. Each ring has a light-colored band, or earlywood, that forms in the spring and a dark-colored band, or latewood, that forms in the summer. The width of the band tells how much the tree grew during that period and therefore can be used as a proxy for the climate during that season. Credit (c) Daniel Griffin, University of Arizona Usage Restrictions This image may only be used to accompany a story about the research described in the release, Monsoon Failure Key to Long Droughts in Southwest 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.