Ecoregions
Locatoins and ages of existing cooperative field trials. The map is divided into U.S. EPA Level IV Ecoregions which delineate areas with similar geology, physiography, vegetation, climate, soils, land use, and hydrology (Gallant et al. 1989, Griffith et al. 1994, Omernik 1995, Omernik et al. 2000).






