Together, the Himalayan mountain system is the planet's highest and home to the world's highest peaks: the Eight-thousanders, including Mount Everest (Nepal/Tibet) and K2 (Northern Areas). To comprehend the enormous scale of this mountain range consider that Aconcagua, in the Andes, at 6,962 m, is the highest peak outside Asia, while the Himalayan system includes over 100 mountains exceeding 7,200 meters.

The Himalayan system, which includes outlying subranges, stretches across six countries: Bhutan, Tibet, India, Nepal, Pakistan and Afghanistan. They are the source of three of the world's major river systems, the Indus, the Ganga-Brahmaputra, and the Yangtze. Approximately 1.3 billion people live in the drainage basin of the Himalayan rivers.

The range proper runs west to east, from the Indus river valley to the Brahmaputra river valley, thereby forming an arc 2,400 km long, which varies in width from 400 km in the western Kashmir-Xinjiang region to 150 km in the eastern Tibet-Arunachal Pradesh region. The Himalaya chain consists of three parallel ranges, with the northern-most range known as the Great or Inner Himalayas.

Location

The Himalayas separate the Indo-Gangetic plain from the Tibetan plateau. The bulk of the mountain range lies in Nepal, Bhutan and the states of Jammu and Kashmir(parts of which are disputed between Pakistan and India), Himachal Pradesh, Uttarakhand, Sikkim and Arunachal Pradesh in India . The outlying parts of the range lie in Tibet, Pakistan (some in disputed territories) and Burma .

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 at 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.