Presently, Manassas National Battlefield has roughly 1,500 acres of managed grasslands and fields that are maintained by different cutting regimes devised to provide habitat for supporting important bird populations. It is estimated that since the mid-1800's, grassland ecosystems in North America have declined by at least 80 percent. In Virginia, grasslands have decreased by 55 percent since 1945. The managed warm season grasslands in Manassas National Battlefield provide a refuge for birds and other grassland species. The park has restored over 500 acres to native warm season grasses that help provide wildlife habitat, prevent erosion and filter nitrates with their deep root system, and maintain water quality by acting as a riparian buffer in areas where trees cannot be planted. These warm season grasses require no fertilization or lime and are adapted to the acidic soils in the park.