Together, the Himalayan mountain system is the planet's highest and home to the world's highest peaks, the Eight-thousanders, which include Mount Everest and K2. To comprehend the enormous scale of this mountain range consider that Aconcagua, in the Andes, at 6,292 m (20,643 ft) is the highest peak outside Asia, whereas the Himalayan system includes over 100 mountains exceeding 7,200 m (23,622 ft).[1]
The Himalayan system, which includes outlying subranges, stretches across six countries: Afghanistan, Bhutan, People's Republic of China, India, Nepal, and Pakistan. Some of the world's major rivers, the Indus, the Ganges, the Brahmaputra, and the Yangtze, rise in the Himalayas, and their combined drainage basin is home to some 1.3 billion people, including the people of Bangladesh. The Himalayas have profoundly shaped the cultures of South Asia; many Himalayan peaks are sacred in both Hinduism and Buddhism.
The main Himalaya range runs, west to east, from the Indus river valley to the Brahmaputra river valley, forming an arc 2,400 km (1,491 mi) long, which varies in width from 400 km (249 mi) in the western Kashmir-Xinjiang region to 150 km (93 mi) in the eastern Tibet-Arunachal Pradesh region. The range consists of three coextensive sub-ranges, with the northern-most, and highest, known as the Great or Inner Himalayas.
Ecology
The flora and fauna of the Himalayas varies with climate, rainfall, altitude, and soils. The climate ranges from tropical at the base of the mountains to permanent ice and snow at the highest elevations. The amount of yearly rainfall increases from west to east along the front of the range. This diversity of climate, altitude, rainfall and soil conditions generates a variety of distinct plant and animal communities.
Lowland forests
On the Indo-Gangetic plain the base of the mountains, an alluvial plain drained by the Indus and Ganga-Brahmaputra river systems, vegetation varies from west to east with rainfall. The xeric Northwestern thorn scrub forests occupy the plains of Pakistan and the Indian Punjab. Further east lie the Upper Gangetic plains moist deciduous forests of Uttarakhand and Uttar Pradesh and Lower Gangetic plains moist deciduous forests of Bihar and West Bengal. These are monsoon forests, with drought-deciduous trees that lose their leaves during the dry season. The moister Brahmaputra Valley semi-evergreen forests occupy the plains of Assam.
The Terai belt
Above the alluvial plain lies the Terai strip, a seasonally marshy zone of sand and clay soils. The Terai has higher rainfall than the plains, and the downward-rushing rivers of the Himalaya slow down and spread out in the flatter Terai zone, depositing fertile silt during the monsoon season and receding in the dry season. The Terai has a high water table due to groundwater percolating down from the adjacent zone. The central part of the Terai belt is occupied by the Terai-Duar savanna and grasslands, a mosaic of grasslands, savannas, deciduous and evergreen forests that includes some of the world's tallest grasslands. The grasslands of the Terai belt are home to the Indian Rhinoceros (Rhinoceros unicornis).
Bhabhar belt
Above the Terai belt is an upland zone known as the Bhabhar, a zone of porous and rocky soils, made up of debris washed down from the higher ranges. The Bhabhar and the lower Shiwalik ranges have a subtropical climate. The Himalayan subtropical pine forests occupy the western end of the subtropical belt, with forests dominated by Chir Pine (Pinus roxburghii). The central part of the range is home to the Himalayan subtropical broadleaf forests, dominated by the sal tree (Shorea robusta).They are at the foot of the himalayas where the himalayan streams descend on to the plains.
Shiwalik Hills
Also called Churia or Margalla Hills, Sivalik Hills is an intermittent outermost range of foothills extending across the Himalayan region through Pakistan, India, Nepal and Bhutan. This region consists of many sub-ranges. Summits are generally 600 to 1,200 metres. Steeper southern slopes form along a fault zone called Himalayan Frontal Thrust (HFT); northern slopes are gentler. Permeable conglomerates and other rocks allow rainwater to percolate downslope into the Bhabhar and Terai, supporting only scrubby forests upslope.
Inner Terai or Dun Valleys
The Inner Terai valleys are open valleys north of Shiwalik Hills or nestled between Shiwalik subranges. Examples include Dehra Dun in India and Chitwan in Nepal.
Lesser Himalaya
Also called Mahabharat Range, a prominent range 2,000 to 3,000 metres high forming along the Main Boundary Thrust fault zone with a steep southern face and gentler northern slopes. Nearly continuous except for river gorges. Rivers gather in candelabra form to the north to break through this range in relatively few places.
Midlands
'Hilly' region (Pahad) averaging about 1,000 metres immediately north of the Mahabharat Range, rising over about 100 km to about 4,000 metres at the Main Central Thrust fault zone where the Greater Himalaya begin.
* Montane forests - At the middle elevations of the range, the subtropical forests yield to a belt of temperate broadleaf and mixed forests, with the Western Himalayan broadleaf forests at the western end of the range, and the Eastern Himalayan broadleaf forests in Assam and Arunachal Pradesh. Above the broadleaf forests are the Western and Eastern Himalayan subalpine conifer forests. Treeline is about 3,500 meters so patchy alpine ecology is found in the highest parts of the midlands.
Greater Himalaya
North of the Main Central Thrust the highest ranges rise abruptly as much as 4,000 meters into the realm of perpetual snow and ice. As the himalayan system becomes wider from east to west, the number of parallel high ranges increases. For example Kagmara and Kanjiroba ranges both reach well over 6,000 meters north of the Dhaulagiri Himalaya in central Nepal.
* Alpine shrub and grasslands - Above the tree line are the Northwestern, Western, and Eastern Himalayan alpine shrub and meadows, which yield to tundra in the higher Himalayan range. The alpine meadows are the summer habitat of the endangered Snow Leopard (Uncia uncia).
Trans-himalaya
The watershed between rivers flowing south into the Ganges or Indus and rivers flowing north into the Brahmaputra or mainstem Indus that flow around the ends of the entire range often follows somewhat lower, less rugged mountains tens of kilometers north of the highest ranges. South-flowing rivers form valleys in this region, often semi-arid due to rainshadow effects. These valleys hold some of the highest permanent villages on earth.
0 comments:
Post a Comment