Measuring Trees (IMAGE) University of Arizona Caption Sean Michaletz (right) and Brian Enquist measure the diameter of a large tree to test a new mathematical theory that assesses the relative importance of several hypothesized drivers of net primary productivity. Credit Enquist Lab Usage Restrictions This visual may only be used in conjunction with reporting/posting of this news release. Image/video credit must be included exactly as indicated. 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.