Forest Overview (IMAGE) Princeton University Caption Princeton University researchers suggest in a new theory of land-biome evolution that plants are not passive features of their environments, but may instead actively behave in ways that determine the productivity and composition of their ecosystems. The theory was developed to explain why trees known as "nitrogen fixers," which produce their own fertilizer from atmospheric nitrogen, flourish in nitrogen-rich tropical soils, but are short-lived in the nitrogen-poor soils of boreal or temperate forests. The aerial photo above shows a rainforest in Panama in which nitrogen-fixing trees are abundant (about 10 percent of all trees), diverse, and persist in both young and old forests. The researchers found that tropical nitrogen fixers evolved to stop producing nitrogen in order to compete with neighboring trees. Credit Photo by Smithsonian Tropical Research Institute, Panama Usage Restrictions None 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.