The polar zone extends beyond 66.5 degrees latitude, both north and south. It is the zone with the coldest year-round climate. The tundra and taiga are the two biomes found in this zone.
The tundra has very short growing seasons, with almost 24 hours of light during the summer and 24 hours of dark during the winter. The very top layer of soil will thaw, but remain muddy. All the soil below this is frozen, and is known as permafrost.
The taiga is located south of the tundra, and is characterized by its coniferous forests. The soil is acidic, and few plants grow on the forest floor. The boundary between the tundra and taiga is called the tree line.