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Fig. 1. The literature reviewed in this paper is categorized as being conducted either within a northern region (USDA Hardiness Zone 5–6) or a southern region (USDA Hardiness Zone 7–8). A winter and a summer cover crop seasonal niche is considered for each of these regions. The northern region is shown in black on the map and includes the Northeast and Upper Midwest. The southern region is shown in gray on the map and includes the Southeast and Zone 7–8 in California.
