When Lewis and Clark saw western Iowa in 1804, the land was almost completely covered with prairie grasses and wildflowers, but very little of this vegetation remains today. The largest tracts of undisturbed prairie in Iowa are in the Loess Hills, where mixed grass prairies include tall grass species such as switchgrass, big bluestem, and Indiangrass, mid-grasses such as little bluestem and sideoats grama, and short grass plants such as blue grama and buffalograss. Prairie wildflowers, called forbs, also share this habitat, including leadplant, compass plant, coneflower, asters, blue-eyed grass, and yucca. In pre-settlement times, wildfires and grazing animals like bison helped prevent trees and shrubs from overtaking these sun-loving prairies, but because most of a prairie grass or flower grows below the soil, the plants could quickly resprout after burning or grazing. Those natural controls no longer exist, so prairie managers now cut woody intruders or use periodic controlled burns. From spring through fall, the prairies show changing blooms and animal life, from pasque flowers protected from frost by hairy stems and leaves to taller midsummer flowers that rise above the grasses for pollinating insects, and autumn goldenrods and sunflowers swarming with soldier beetles.