The coastal prairie, located along the coastal plain of southwestern Louisiana and southcentral Texas, is the southernmost tip of the tallgrass prairie ecosystem so prevalent in the Midwest. This region is distinctive from the Midwestern grasslands in the amount of rainfall: 142.24 cm (56 inches) annually compared to a mere 71 cm (28 inches) in the Midwest. Such an abundant amount of rainfall typically produces forests rather than grasslands; scientists believe that the coastal prairie developed because of the hard clay layer underneath the topsoil, which inhibited root formation of larger species such as forest trees. Before settlement, natural fires such as those set by lightning also contributed to keeping the growth of trees and shrubs in check while stimulating the growth of native grasses.