Between the forests to the south and the arctic ocean and polan icecaps to the north lies a circumpolar band of about 5 million acres of treeless country called the arctic tundra. Smaller, but ecologically similar, regions found above the tree limit on high mountains are called alpine tundras. As is deserts, a master physical factor rules these lands, but it is heat rather than water that is in short supply in terms of biological function. Precipitation is also low, but water as such is not limiting because of the very low evaporaton rate. Thus, we might think of the tundra as an arctic desert, but it can best be described as a wet arctic grassland or a cold marsh that is frozen for a portion of the year. 

      Although the tundras are often known as the ‘’barren grounds’’ and may be expected to have a relatively low biological productivity, a surprisingly large number of species have evolved remarkable adaptations to survive the cold. The thin vegetation mantle is composed of lichens, grasses, and sedges, which are among the hardiest of land plants. During the long daylight (long photoperiod) of the brief summer the primary production rate is remarkably good where topographic conditions are favorable (as in low lying areas). The thousands of shallw ponds, as well as the adjacent arctic ocean, provide additional food to tundra food chanis. There is enough combined aquatic and terrestrial net production, in fact, to support not only thousands of breeding migratory birds and emerging insects during the summer, but also permanent resident mammals that remain active throughout the year. The latter range from large animals such as musk ox, caribou, reindeer, polar bears, wolves, and marine mammals, to lemmings that tunnel about in the vegetation mantle. The large land herbivors are highly migratory, since there is not enough net production in any one local area to support them. Where man tries to ‘’fence in’’ these animals or select for domestication nonmigratory strains, such as domestic reindeer, overgrazing is almost inevitable unless judicious ‘’rotating the pastures’’ is employed to offset the absence of migratory behavior. The dramatic ups and downs in the density of lemmings was discussed on this post. the difference in response to light by plants in the arctic and alpine tundras was mentioned in thispost. Man’s impact on the tundra will increase as he strives to exploit oil and mineral resources from polar regions. Its special fragility need to be recognized when roads and pipelines are built.