Grasslands are among the most biologically productive yet endangered ecosystems on Earth and are the major ecosystem of the Great Plains, where prairie shapes the cultural landscape and supports the interaction and survival of plants and animals. At Sand Creek Massacre NHS, the prairie includes sandhills, shortgrass and mixed grass prairie, and wetlands, and the diversity of upland grassland and riparian areas provides important habitat for birds, especially migrating species, and other animals. Cottonwood trees along Big Sandy Creek, both living and dead, hold cultural and spiritual significance to the Cheyenne and Arapaho beyond their association with the Indian encampments attacked by the U.S. military in 1864 during Sand Creek Massacre, and during severe winters American Indians and early settlers fed cottonwood to horses and cattle. The cottonwood stands lining Big Sandy Creek date to the mid 1900s, though a few trees may have been present during the massacre as seedlings or saplings, and the trees provide roosting, nesting, feeding sites, and nesting material for birds. Historic disturbances and drought have affected the park's vegetation composition, and changes since the massacre may relate to introduced exotic species, changes in fire frequency, agricultural and development disturbances, drought, and canal construction. Few grasslands are preserved in the southern Great Plains, and protected areas are especially important despite degraded conditions caused by row cropping, exotic vegetation, altered hydrology from damming and pumping for irrigation and development, livestock and human traffic, and woody shrub encroachment. Even so, some degraded areas at Sand Creek Massacre NHS and other parks remain natural oases in a largely agricultural landscape and are candidates for restoration. In 2008, the National Park Service's Southern Plains Network began planning prairie restoration projects in several parks, including Sand Creek Massacre NHS, and restoration requires an indefinite commitment and monitoring so adjustments can be made over time. Preserved and protected areas at Sand Creek Massacre NHS and other National Park Service units also provide opportunities for scientific investigation as reference points for comparison with altered environments. Studies there contribute to understanding the area and inform planning, management, decision making, work with partners and agencies, and communication with the public to protect natural systems and native species. Research covers archaeology, geology, soil, fish, birds, plants, and water, and decades of cooperation among tribes, state and federal agencies, universities, and affected landowners contributed to the establishment of the Sand Creek Massacre Site as a National Park Service unit in 2007. Continued study will expand knowledge of the resources preserved and protected there.