On the Himalayan Uplift and Himalayan Corridors

Abstract

Himalayan corridors Kitamura (1955) postulated that the temperate zone of the southern side of the Great Himalayas represented a corridor through which Sino-Japanese plants migrated westwards, and named it the Himalayan corridor. However, he did not pay much attention to the eastward distribution of Mediterranean elements through the corridor and extended the Sino-Japanese region up to Afghanistan by drawing the Himalayan corridor (Kitamura, 1957). The southern slopes in the Himalayas are generally drier than the northern slopes. In the case of the Great Himalayas, however, the south-facing slope is moister than the north facing one. Therefore, there are two corridors along the Outer and Lesser Himalayas respectively, on the south facing slopes and on the north facing slopes, and the Great Himalayas provide a corridor on its southern slope. The northern side of the Great Himalayas can not act as a corridor due to its dryness. The eastern elements extended their distribution range westwards through the moister corridor and the western elements migrated eastwards through the drier corridor. However, for example, wet sal (Shorea robusta) forest occurring on the south-facing slopes of the Siwalik range in Central Nepal can not survive on the south facing slopes in the western Siwaliks. It moves to the north-facing slope and it is replaced by the dry hill sal forest in the west Siwalik range. The dry hill sal forest gives place to the subtropical decidous hill forest dominated by Anogeissus latifolia in the west Siwalik. The deciduous hill forest dominated by Anogeissus latifolia is replaced by the subtropical scrub composed of Olea cuspidata, Dodonea viscosa etc. in the further west. On the north-facing slope, the wet Sal forest replaces Castanopsis indicaSchima wallichiana forest in the west Siwalik where the dryness caused by the increase of mediterraneity of climate is prevailing. The Siwalik range provides corridors on the south and north sides of the range for the eastward migration of western elements and westward distribution of eastern elements. In the Lesser Himalayas, Quercus lanuginosa-Q. incana forest is replaced by Q. incana forest in West Nepal, and Q. incana forest occurs on the all exposures in West Nepal and Kumaon region in India and then it is confined to the northern side of the Lesser Himalayas westwards. Cedrus deodara forest replaces Q. incana forest on the southern slopes of the western Lesser Himalayas where Q. incana forest move to the northern side. The Himalayan corridors are twisted in this way.