ABSTRACT
The variations of temperature and rainfall which mountains bring about are sudden and abrupt, so that the climatic optimum may be displaced within a very short distance from one vegetation type to another. The climatic conditions here are in strong contrast with those experienced by the corresponding vegetation in Arctic climates, where the sunlight from the low-angled sun is weak, where the soil is poor and acid, ill-drained and saturated with ice-cold water. The far-reaching results of this difference will be seen later when the relation of climate to vegetation and the habitability of the zones are discussed. The Himalaya Mountains, like the Alps, function as a climatic divide, barring the way against the summer monsoon purely by virtue of their relief. To the north of them lies the lofty plateau of Tibet whose northern rim is the Kuen Lun, beyond which lie the desert depressions of Eastern Turkestan and the Tsaidam.
