Life Zone Ecology of The Bhutan Himalaya II.

点击翻译按钮获取中文摘要

Life Zone Ecology of The Bhutan Himalaya II.The second phase study is focused on the subtropical part of the Bhutan Himalaya. Climatic analysis of the dry valley along the Sankosh river clarified the main factor which cause the occurrence of dry valley is the strong southerly (valley) wind which reach maximum velocity at 14 or 15 local time when the temperature reaches maximum. The high temperature, the large gradient of water vapour pressure and the strong wind make the evapo transpiration large. Landform and tectonic movement of Bhutan was studied in middle reaches of several main rivers. Bedding planes of older fluvial deposits at the Wangdiphodrang Dzong indicates the relative uplift of the lower reaches from WangdiyPhodrang against the upper ones and suggests the uplift of the southern High Himalaya belt.Vegetation structure and its human modification were studied in the subtropical zone ranging from 1000 to 2500 m. In natural forests, there are many tropical elements such as Altingia excelsa, Exbucklandia populnea, Sloanea sterculiaceus, Toonaciliata, Acrocarpus fraxinifolius, etc. , however, the repeated human disturbances such as shifting cultivation and coppicing had modified the forests into less diversified lauro-fagaceous forests. The pattern is further intensified by xeric-mesic gradients along the topo-edaphological gradients, and grazing by domestic animals. Farmland weeds and pastures were studied extensively. A dwarf bamboo grasslands like Pleioblastus pastures on Mt. Aso and Mt. Kuju was found in central Bhutan which is dominated by dwarfbamboo, Yushania. It is an evergreen bamboo grazed by cow and Yaku throughout the year. Grasslands are also modified into waste lands dominated by Artemisia, Senecio, Rumex and Arundinaria.