The Tallgrass Prairie Preserve is the largest protected remnant of tallgrass prairie left on earth. Originally spanning portions of 14 states from Texas to Minnesota, urban sprawl and conversion to cropland have left less than 10% of this magnificent American landscape. Since 1989, the Nature Conservancy has proven successful at restoring this fully-functioning portion of the tallgrass prairie ecosystem with the use of about 2500 free-roaming bison and a "patch-burn" model approach to prescribed burning.