Transhumance A final illustration of population movements which are closely associated with ecological factors concerns transhumance or semi-nomadic pastoralism, which is prevalent in the more mountainous parts of the Third World. Transhumance involves the periodic shift of small numbers of population between different environmental zones (typically upland and lowland) in response to prevailing climatic and ecological conditions.• Transhumance is widely practiced in the mountainous regions of the South Asian sub-continent. Approximately one-fifth of the land area of Tibet is roamed by nomadic pastoralists. In the Swat region of Pakistan, semi-nomadic Kohistanis move annually between altitude belts, ranging from 2,000-14,000 feet. Because of prevailing ecological conditions in north-western India it is not possible to graze livestock year-round in one area. With the onset of the monsoon, livestock are moved from Gujarat towards the sub-mountainous regions of Rajasthan. The vacated lowland fields are then used to grow arable crops. After the harvest, around December, the herds return to graze in the lowlands.