Temperature and rainfall are the two most important things for forests. Many places are too cold or too dry for them. Forests can exist from the equator to near the polar regions, but different climates have different kinds of forests. In cold climates conifers dominate, but in temperate zone and tropical climates forests are mainly made up of flowering plants. Different rainfall also makes different kinds of forest. No forests exist in deserts, just a few trees in places where their roots can get at some underground water.