The plant community in an area is the most sensitive indicator of climate. Areas with moderate to high temperatures and abundant rainfall throughout the year are heavily forested (unless humans have cleared the land for agriculture!). Areas with somewhat less rainfall are mainly grasslands, which are called prairies in North America. Humans have converted grasslands into rich agricultural areas around the world. Even in areas with high yearly rainfall, trees are scarce if there is not much rainfall during the warm growing season. Regions with not much rainfall and scarce vegetation are called deserts, or arid regions. Areas with somewhat greater rainfall are called semiarid regions. The problem with semiarid regions is that when humans use them for agriculture, the loss of natural vegetation can cause the areas to become deserts.