Extensive research has been conducted in the tundra of Russia-Siberia over the last few hundred years with volumes of results published. A latitudinal zonation of plant communities in northern Russia consists of three tundra types: Arctic, Typical and Southern. However, all three tundra types are contained within the treeless territory surrounding the North Pole that is commonly referred to as Arctic. Precipitation in the tundra varies with distance to the ocean; the arctic tundra bordering the Arctic Ocean receives 200-250 mm (8-10 in) per year and the typical and southern tundra types receive 300-350 mm (12-14 in). Around 25-30% of the total solar radiation received in the tundra regions occurs in June.