Physiographic and ecological study of mountain geography as exemplified in the Himalaya
Altitude, as well as latitude, is one of the factors which most strongly influences the climatic environment. The regular reduction of temperature and atmospheric pressure with altitude, and the inverse variation in humidity, produce a zonation of the total environment, primarily for vegetation, and secondarily, in partial dependence on vegetation, for animal life. These vertical zones correspond closely with the latitudinal climatic zones which surround the poles, but their much closer geographical relationship in mountatns makes them more immediately evident. It is, therefore, the purpose of this study to analyse the physical and climatic factors, and how they limit the distribution of organisms. Ultimately, the aim is to formulate some generalisations as to the characteristic changes that occur with increasing altitude. The Himalaya was chosen for this study, first, because the direction of the mountain range has an important influence on the attendant climatic effects. Since the Himalaya is roughly parallel to the lines of latitude, it coincides in general with the climatic limits, and intensifies them. Second, the relatively low latitude position of the Himalaya affords the opportunity to include in the study every climatic environment between the tropical zone and the alpine zone. Third, the altitude ranges from nearly sea level to the highest mountains in the world in less than 150 miles, thus confining the range of climatic zones to a relatively short distance.