A biome is a major terrestrial community characterized by a distinct climate and inhabited by a particular species of plants and animals. Tundra is characterized by precipitation of less than 25 cm annually. Permafrost or permanent ice is found about a meter down from the surface, it never melts and is impenetrable to both water and roots. Savannahs are open grasslands with scattered shrubs and trees. Coniferous forest contain evergreen trees. In these forests all plants do not shed their leaves at the same time hence forest remains always evergreen. But Prairies is a grassland and epiphytes and ephemerals are found in deserts.