Moving westward, the amount of annual precipitation decreases. The tallgrass prairie transitions to mixed prairie, with grasses between two and four feet. Great fluctuations in rainfall may occur from year to year. Wind is an important factor in the climate. Water evaporates, contributing to already arid conditions.
Wind also contributes to the spread of wild fires.
Fire plays an important role in the grassland ecosystem. Most trees are killed or weakened by fire, but grasses have adapted to survive it and many even grow better after they have been burned.