The area lying above 66.5° North that is dominated by the Arctic Ocean but also includes large land areas in Canada, Russia, Greenland, Scandinavia, Iceland, and Alaska. Some of the land areas, including most of Greenland, are permanently covered in ice and pack ice is common throughout the Arctic Ocean. Climate in this high latitude zone is extreme, with short cool summers and long cold winters. Temperatures are particularly low in the interior—average mid‐winter temperatures on the Greenland ice cap are around −33°C, for example. Precipitation is generally low (less than 250 millimetres a year on average), and well distributed throughout the zone. Large river and lake systems are rare, because of the low precipitation, but shallow lakes, ponds and marshes are common in areas underlain by permafrost. Although the Arctic has the appearance of a vast, frozen desert, it does support wildlife. Signs of life are difficult to find during the cold, dark winter months but some species of mammals and birds carry extra insulation (such as fat) to survive the winter. The Arctic appears to wake up in spring. More than 400 species of flowering plant grow in the Arctic, and most of the land which is not covered in ice is tundra, with a natural vegetation of low creeping shrubs, grasses, thick growths of lichens and mosses, and herbs and sedges. The Arctic region is home to a wide variety of birds and fish, and the mammals include polar bear, arctic fox, arctic wolf, walrus, seal, caribou, reindeer, the infamous lemming, and many species of whale.