Fence posts standing in the middle of the prairie marked the former edge of a farm field. In 1974, the Minnesota Historical Society planted a few grass varieties on 50 acres of cropland, beginning one of the first prairie reconstruction projects in Minnesota. Recreating prairie raises difficult questions because the original prairie supported a great variety of plants, several hundred species of birds, 80 species of mammals, and thousands of types of insects. Reconstructing it as it once was requires a specific climate, periodic fire, and large grazing animals. Some scientists believe prairie reconstruction takes two to five hundred years, while others believe that once native prairie is destroyed, it is gone forever.