Native prairie is a highly diverse plant community, with more than 100 different plant species sometimes found in fewer than 5 acres. Intact prairie sod can absorb up to 9 inches of rain per hour, helping prevent flooding, and prairie plants store carbon in the soil through their root systems, helping slow climate change. In late spring and late summer, many wildflowers are in bloom. For thousands of years, Plains Indians relied on prairie plants for food, medicine, and other needs. Dakota and Lakota people brewed tea from purple coneflower to relieve pain, people of the Cheyenne tribe used its tincture to treat snake bite and poison ivy rash, the Lakota roasted woolly verbena nutlets and ground them into a nutritious meal, the Dakota used an extract from silverleaf scurfpea to wash their horses' wounds, and various Plains tribes extracted oil from sunflower seeds for cooking and for their hair. National wildlife refuges protect habitats ranging from arctic tundra and prairie grasslands to subtropical wetlands, supporting more than 700 bird species, 220 mammal species, 250 reptile and amphibian species, and more than 200 fish species. Administered by the U.S. Fish and Wildlife Service, the National Wildlife Refuge System protects and manages more than 150 million acres in more than 550 refuges across all 50 states and U.S. territories. These refuges have helped the bald eagle flourish again across America, protect brown bears in Alaska, provide nesting habitat for elegant terns in San Diego National Wildlife Refuge, support northern pintail and other waterfowl at Arrowwood National Wildlife Refuge in North Dakota, and offer major migration, breeding, resting, and nesting habitat for cranes, waterfowl, shorebirds, grassland birds, and other wildlife. National wildlife refuges also offer recreation including wildlife observation, environmental education, hunting, and fishing, and the National Elk Refuge in Jackson, Wyoming, holds one of the world's largest wintering concentrations of elk.