The entries in subject encyclopedias are written by scholars in the field, and often include recommended readings or bibliographies. The first two encyclopedias here are about environmental history and issues generally, and may provide theoretical background and comparative case studies. The second two are encyclopedias of the American South, and contain entries or sections devoted to environmental aspects of Southern history and experience.
Encyclopedia of World Environmental History by 
Encyclopedia of Global Change by 
The New Encyclopedia of Southern Culture by 
The South by The Cambridge Histories Collection includes multi-volume works on many geographical units and historical themes, and can help you with the general narrative of a time period and major academic debates on the issues.
