The Forest Service (USDA) operates 83 Experimental Forests and Ranges (who knew?) where intensive scientific study is undertaken to map diverse ecological sites. Among the many goals of their work, the Forest Service aims to 1. Develop of systems for managing and restoring forests, rangelands, and watersheds; 2. investigate the workings of forest and stream ecosystems; 3. characterize plant and animal communities; and 4. observe and interpret long-term environmental change. You can learn more about the freely available data and publications on their website.