18 THE TUNDRA AND ITS FAUNA 



drains away as the snow melts is favourable to plant 

 growth, while level ground is very unfavourable. A 

 sunny exposure also exerts much influence. The Sver- 

 drup expedition noted that the Arctic hare is prac- 

 tically Umited to the regions where large valleys open 

 out into fiords, for only here is vegetation abundant 

 enough to supply its needs. 



As regards topography one must note that the tundra, 

 like the semi-arid lands of other latitudes, is charac- 

 terized by a very youthful condition of drainage. As 

 already stated, the rivers are temporary, chemical 

 erosion does not occur, and therefore the process of 

 carving up the land into hill and valley goes on very 

 slowly, and the land is imperfectly drained. The 

 imperfect drainage is aided by the fact that the ex- 

 treme coldness of the soil is unfavourable to bacterial 

 life, and thus humus accumulates and favours the 

 growth of bog mosses as contrasted with higher plants. 

 These hold up the water like a sponge, and so hinder 

 drainage. When Nansen and his party left the inland 

 ice of Greenland they descended to a little tarn, whose 

 water drained by a stream to the distant fiord. In 

 their descent, as the leader notices, they found that the 

 main streams had often transverse tributaries, which 

 greatly hindered progress. The picture may be taken 

 as characteristic of the tundra. Lakes fed by melting 

 ice, streams showing a very undeveloped drainage 

 system — ^these are characteristic featvu-es, which, aided 

 by the climate, accoimt for the very local development 

 of a covering of vegetation, and therefore for the 

 ciuiously local appearance of animals. 



Without discussing the plants of the timdra in detail 

 we may note those points which are of special impor- 

 tance for animal life. The first of these is the great 



