A prescribed burning of prairie at the Flying W Ranch near Clements, Kansas travels down a hillside during "Flames in the Flint Hills." This agritourism event allows ranch guests to take part in lighting the prescribed burns. Prairie grasses in the Kansas Flint Hills are intentionally burned by land mangers and cattle ranchers in the spring to prepare the land for cattle grazing and help maintain a healthy tallgrass prairie ecosystem. The burning is also an effective way of controlling invasive plants and trees. The prairie grassland is burned when the soil is moist but grasses are dry. This allows the deep roots of the grasses to survive and the burned grasses on the soil surface return as nutrients to the soil. These nutrients allow for the rapid growth of new grass. After approximately two weeks of burning, new grass emerges. Less than four percent of the original 140 million acres of tallgrass prairie remains in North America. Most of the remaining tallgrass prairie is in the Flint Hills in Kansas.