The original diversity has survived in the Loess Hills in large part because the rugged hills have remained relatively remote and isolated, resisting conversion to cropland, lawn, pasture, and settlement. More than 700 species of vascular plants have been identified in the Hills. Remaining native prairies are large enough to maintain viable populations of rare butterflies that have declined or disappeared on smaller prairie remnants elsewhere. The wildness of the region also allows safe refuge for wintering hawks, rare species such as bobcat, secretive lizards and snakes, and numerous other types of animals, many of which are uncommon or absent elsewhere in Iowa and Missouri.
Cornelia F. Mutel, Fragile Giants: A Natural History of the Loess Hills