Nanjemoy IBA is part of the ?green thumb? of southwestern Charles County and contains a large block of contiguous forest. A portion of the area is owned and managed by the Maryland DNR and the U.S. Department of the Interior-Bureau of Land Management, comprising 826 ha of the Nanjemoy Natural Resource Management Area. Other lands within the IBA that are owned and managed by Maryland DNR include the 726 ha Doncaster Demonstration Forest. An additional 1,238 ha of the IBA are protected by The Nature Conservancy as the Nanjemoy Creek Preserve. Forested land cover comprises about 81% of the entire IBA. Agricultural uses account for about 11% of the total area while woody and herbaceous wetlands make up about 4%. The majority of forested habitats include are represented by the oak-hickory association with the remainder consisting of loblolly-shortleaf-pine, maple-beech-birch, and oak-pine. Canopy species include various oaks and hickories, tulip poplar, American beech, red maple, sweet gum, black gum, loblolly pine, and Virginia pine. The majority of the forest is mature; however, there are scattered pockets of young pine and oak-pine forests. Understory species include American holly, mountain laurel, and flowering dogwood. Other habitat features include tidal wetlands along Nanjemoy Creek and Thorne Gut, and pockets of flooded forested wetlands along streams throughout. The entire area is rich in biodiversity and supports a number of rare plant species.
The rich forests of Nanjemoy support a highly diverse assemblage of Forest Interior Dwelling Species (FIDS) ? birds listed by the Maryland Department of Natural Resources as requiring large, intact forest interior habitat to breed successfully. Nanjemoy has 20 FIDS which breed regularly in the IBA out of 25 potentially regular breeders in Maryland?s Coastal Plain forests. In addition to this high FIDS diversity, the site also sustains significant state-level populations for six at-risk species. Included among these are four Audubon/American Bird Conservancy Watchlist (Category Yellow) species: Wood Thrush, Worm-eating Warbler, Prothonotary Warbler, and Prairie Warbler. Eastern Whip-poor-will and Bald Eagle, both at-risk in Maryland, also have significant populations at the site.