A biome characterized by treeless vegetation populated by mosses, lichens, herbaceous perennials, dwarf shrubs and grasses. Tundras are found in the Arctic and on top of mountains where the climate is cold and windy with very little rainfall. Such areas are often underlain with permafrost. Plants and animals that populate Arctic tundras are vulnerable to environmental stress. Scientists have observed that today's tundras are changing dramatically due to global warming.