Article: Forests cover 24 percent of Oklahoma and prairie grasslands composed of shortgrass, mixed-grass, and tallgrass prairie, harbor expansive ecosystems in the state's central and western portions, although cropland has largely replaced native grasses. Where rainfall is sparse in the western regions of the state, shortgrass prairie and shrublands are the most prominent ecosystems, though pinyon pines, red cedar (junipers), and ponderosa pines grow near rivers and creek beds in the far western reaches of the panhandle. Southwestern Oklahoma contains many rare, disjunct species including sugar maple, bigtooth maple, nolina and southern live oak.

Now answer this question: What part of Oklahoma has low rainfall?
western