Possible impact from global warming which is having a greater impact in the tundra than elsewhere. Threat of pollution . Circumpolar in northern hemisphere . Alaska and Canada to northeastern and Great Lakes region of the United States - see this summary site . The growing season is 90 to 120 days per year.
Snow is common.
Fire and insect pests are an occasional factor. Northern edge defined by a timberline 2. The latter is a deciduous conifer, meaning that the needles fall away each winter. Shallow ponds or lakes to peat bogs to graminoids to shrubs to trees. Wolves, bear, lynx, wolverine, fox.