Nearly 600 terrestrial ecological systems in the United States, southern Alaska, and adjacent areas of Mexico and Canada are summarized in this report, which introduces and outlines the conceptual basis for a mid-scale classification unit: the ecological system.
Ecological Systems of the United States
Comer PJ, Faber-Langendoen D, Evans R, Gawler SC, Josse C, Kittel G, Menard S, Pyne M, Reid M, Schulz K, Snow K, and Teague J. 2003. Ecological Systems of the United States: A Working Classification of U.S. Terrestrial Systems. NatureServe, Arlington, Virginia.