when a moderate rainfall area had wetter years, many trees began growing. when there were drier years, fires of ten occurred and killed off the small trees. However, the fires did not kill most grasses. Therefore, prairies with grassland won out in the open areas. Where the areas were most moist and protected, forests grew.
rainfall averaged between 25 cm per year and 100 cam per year in the prairie regions. the eastern parts of the prairie usually received more rainfall that the western parts of the prairie. the difference in rainfall is onereason why the food chain varied somewhat from east to west in the prairie ecosystem.
