CHAPTER XXIV 

 ALPINE ANIMALS 



The plant and animal life of mountains undergoes conspicuous 

 changes at higher altitudes. Intermediate heights, in so far as they are 

 wooded, have a fauna much like that of the near-by forested low- 

 lands. As the conditions for forest growth become unfavorable with 

 increasing altitude and coniferous forests replace the mixed hard- 

 woods, the fauna also becomes less varied. At still higher altitude with 

 lower temperatures and shorter duration of summer, tree growth 

 ceases and new and peculiar environmental conditions present them- 

 selves; in other words, the characteristic high-mountain fauna ap- 

 pears. 



The region above the timber line is called the alpine zone. Few 

 even of the higher peaks and ridges in low mountains such as the Hartz 

 in Germany, or the Appalachians in North America, extend into this 

 treeless zone. Alpine conditions are much better defined when the peaks 

 extend upward into the zone of eternal snow, which flows down into 

 the valleys as glaciers. The zone between the snow line and timber 

 line may be subdivided into a shrub zone, with stunted bushes and 

 recumbent trees, a meadow zone with grasses and herbs, and a sub- 

 snow zone of isolated rocks and patches of ground which merges into 

 the snow zone proper above. The altitude of the timber line depends 

 on the latitude of the mountain range and on the direction of the slope, 

 especially if north or south. The forests reach 4600 m. in Tibet; the 

 alpine zone begins at 3600 m. on the south slope of the Himalayas, 

 and at 2800 m. in the Colombian Andes; in the western United States 

 timber line varies even at the same latitude (48° N.) from an altitude 

 of 3500 m. in the Rocky Mountains to 2000 m. on Mount Rainier. In 

 arctic Norway, at 74° N. latitude, it is only 260 m. above sea level. 

 The alpine fauna ranges downward into the forest zone along the 

 glaciers, which may descend far below the normal timber line. 



The peculiarities of the high mountain environment consist of the 

 high altitude above sea level and the correlated phenomena of reduced 

 atmospheric temperature and pressure and increased humidity, and in 

 the steepness of the slopes, which combine to make such areas inaccessi- 

 ble and unfavorable to life. The isolation of high mountain areas from 



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