Mammals and birds that eat these fish will, in turn, accumulate even greater concentrations of the chemicals. This process is called biomagnification. To make matters worse, the chemicals that accumulate and concentrate also remain in living tissues the longest, some for decades. In general, vegetation and biodiversity decrease toward the north. 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.