Naturalism - A definition of naturalism from the "Glossary of Literary Theory" by Greig E. Henderson and Christopher Brown. - http://www.library.utoronto.ca/utel/glossary/Naturalism.html
EnviroArts - Emphasizes the literary and visual arts in relation to nature, with poetry and essays by contemporary authors (culled mostly from the pages of Orion and Orion Afield magazines--which co-sponsor this site) and information on historic naturalism and natural - http://arts.envirolink.org/
Naturalism: A Brief Introduction - Site includes selected bibliography and definitions of Naturalism by Frank Norris and Lars Ahnebrink. - http://www.csustan.edu/english/reuben/pal/chap6/6intro.html