Ecology

Ecology

Everest, the highest peak of the Himalayas (left) and Lhotse (right), no. 5

K2, on the border of Pakistan and People's Republic of China

Kangchenjunga, on the border of Nepal and Sikkim, India

The flora and fauna of the Himalayas vary 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. In fact the extrema of high altitude (low atmospheric pressure) and very cold at the most elevated reaches allow extremophile organisms to survive.^[4]

Lowland forests

On the Indo-Gangetic plain at the base of the mountains, an alluvial plain drained by the Indus and Ganges-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 (2,000 to 3,900 ft). 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. The Himalayan subtropical pine and broadleaf forests continue here.

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. Himalayan subtropical broadleaf forests grow here.