Along the northern reaches of the continents is the Arctic desert. Plants grow in compact cushions for protection against the severe climatic conditions. To the south is the high Arctic tundra, consisting largely of herbs and mosses. Still farther south is the low Arctic tundra, found in northern Alaska, southern coastal areas of Greenland, and Russia. The vegetation here consists of dwarf shrubs, mosses, sedges, grasses, and lichens.
Tundra is separated from the boreal forest of the subarctic region by the treeline.
The treeline is defined as the absolute northern limit of tree-like species. It generally follows the 10deg. C July isotherm and is sometimes used to define the southern limit of true Arctic conditions. The terrestrial contaminant pathway is from the air to the plants and then to the animals. Feeding on the Arctic tundra, northern grazing mammals ingest pollutants deposited from the atmosphere.