When the federal government took land for the development of nuclear weapons technology, its acquisitions included large buffer areas for safety and security that surround the major research and production facilities. The agricultural and forest land that was taken has been mostly undisturbed since the initial acquisition, resulting in large, contiguous forest tracts of varying age. Protected from fragmentation and disturbance over the ensuing decades, these areas evolved into ecological sanctuaries of remarkable size and diversity that contain species and ecological communities now absent or uncommon in surrounding areas. The Oak Ridge Reservation is the largest tract of relatively unfragmented native forest habitat remaining in the Southern Ridge and Valley of East Tennessee, and contains more species of breeding birds than any other single tract of land in Tennessee. The ORR is home to state-listed threatened and endangered plants, federally and state-listed animal species, with appropriate habitat for additional listed wildlife species. Natural areas and reference areas containing habitat suitable for threatened and endangered species have been designated for protection from development.