Life Zone Ecology of The Bhutan Himalaya II.

不丹喜马拉雅山脉生命带生态学2.第二阶段研究集中在不丹喜马拉雅山脉的亚热带部分。通过对桑科什河干谷的气候分析，明确了造成干谷发生的主要因素是当地时间14~15时达到最高气温的强偏南(谷)风。气温高，水汽压梯度大，风大，蒸散量大。研究了不丹在几条主要河流中游的地貌和构造运动。研究了海拔1000~2500米的亚热带地区的植被结构及其人为改造。天然林中有许多热带成分，如红豆杉、香椿、毛竹、香椿、毛果等。然而，由于反复的人为干扰，如轮垦、采伐等，使森林变成了多样性较低的落叶松林。沿地貌-土壤梯度的干旱-中生梯度和家畜的放牧进一步强化了这种格局。对农田杂草和牧场进行了广泛的研究。一片矮小的竹子草原，像竹林一样在山上放牧。麻生太郎和Mt.Kuju发现于不丹中部，那里以矮竹Yushania为主。它是一种常青竹，牛和雅库一年四季都在吃草。草原也被改造成以艾属、千里光、鲁梅克斯和青蒿属为主的荒地。

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.