Measuring Mature Trees (image) Smithsonian Tropical Research Institute Share Print E-Mail Caption Luis Aguilar measures tree diameter. More than 200,000 trees are measured every five years in a primary forest in the Smithsonian's ForestGEO network plot on Barro Colorado Island in Panama. Credit Sean Mattson, STRI Usage Restrictions Credit: STRI 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.