Tundra is a treeless, level or gently undulating plain characteristic of Arctic and sub-Arctic regions. The main swathe of tundra occurs in the Northern Hemisphere, running across northern Canada and Eurasia.
For most of the year the temperature is than 0°C, and even during the short summer it never rises above 10°C (50°F). During winter, temperatures can fall to -30°C (-86°F). For six to nine month the average temperature is below freezing point, and there is a thick layer of permafrost, of which only the top few centimeters thaw out in the summer. Where melting occurs, the land is wet and marshy, an ideal breeding ground for mosquitoes. The wet tundra soils are gleys, and waterlogging is characteristic. Tundra vegetation includes lichens, mosses, stunted shrubs, and, in summer, small flowering plants.
Similar regions on high mountains (but generally without permafrost) are called alpine tundra.