Flux Tower (IMAGE) University of Arizona Caption A flux tower at the Harvard Forest Environmental Measurements Site is shown. Equipped with various instruments, the towers are capable of measuring the ratio of carbon isotopes -- among other parameters -- above the tree canopy with very high accuracy. Credit Richard Wehr, University of Arizona Usage Restrictions This image may only be used in conjunction of reporting/posting of this news release. Credit must be stated 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.