Eastern Himalayas

TheEastern Himalayasextend from easternNepalacrossNortheast India,Bhutan,theTibet Autonomous RegiontoYunnaninChinaand northernMyanmar.The climate of this region is influenced by themonsoon of South Asiafrom June to September.It is abiodiversity hotspot,with notablebiocultural diversity.

A political/geographical representation of the Eastern Himalayas. Image credits:ICIMOD

Geologic strata

The EasternHimalayashas a more varied geomorphic history and pervasive topographic features than the Central Himalayas. In the southwest of theSub-Himalayaslies theSingalila Ridge,the western end of a group of uplands in Nepal. Most of the Sub-Himalayas are in Nepal; a small portion reaches into Sikkim, India and a fragment is in the southern half of Bhutan. The region's topography, in part, has facilitated the region's rich biological diversity and ecosystem structure.

The Buxa range of Indo-Bhutan is also a part of the ancient rocks of the Himalayas. The ancient folds, running mainly along an east-west axis, were worn down during a long period ofdenudationlasting intocretaceoustimes, possibly over a hundred million years. During this time thecarboniferousandpermianrocks disappeared from the surface, except in its north near Hatisar in Bhutan and in the long trench extending fromJaldhaka RivertoTorsa River,wherelimestoneandcoaldeposits are preserved in discontinuous basins. Limestone deposits also appear in Bhutan on the southern flanks of the Lower Himalayas. The rocks of the highlands are mainlysandstonesof theDevonianage, with limestones and shales of the same period in places. The core of the mountain is exposed across the centre, wherePaleozoicrocks, mainlyCambrianandSilurianslatesand Takhstasang gneiss outcrops are visible in the northwest and northeast, the latter extending to westernArunachal Pradeshin India.

In theMesozoicera the whole of the worn-down plateau was under sea. In this expansive shallow sea, which covered most ofAssamand Bhutan,chalkdeposits formed from seawater tides oscillating between land and sea levels. During subsequent periods, tertiary rocks were laid down. TheParometamorphic belt may be found overlying Chasilakha-Soraya gneiss in some places. Silurian metamorphics in other places suggest long denudation of the surface. This was the time ofAlpinemountain and large number of "active volcanoes" formation which act as backbone of the Himalayas and much of the movement in thepalaeozoicregion was probably connected with it. The Chomolhari tourmaline granites of Bhutan, stretching westwards from the Paro Chu and adds much depth below the present surface, were formed during this period of uplift, fracture and subsidence.

Climate

The climate of the Eastern Himalayas is of a tropicalmontane ecosystem.The tropical rainforest climate is hot and wet all year round, with no dry season in the foothills inKöppen Climate Classification System(Af), and chilly winters mainly on higher elevations. The hot season commences around the middle of April reaching its maximum temperature in June, and finishing by the end of August. The average summer temperature is generally 20 °C (68 °F). The average annual rainfall is 10,000 mm (390 inches). A significantly large amount of snowfall is rare, and it is uncommon even at higher elevations. This belt of Himalayas is wetter as it receives more rain than the drierWestern Himalayas.

In the valleys ofRangeet,Teesta,andChumbimost precipitation during winter takes the form of snowfall. Snow accumulation in the valleys greatly reduces the area's wintertime temperature. The northeast monsoon is the predominant feature of the Eastern Himalayan region's weather, while on the southern slopes cold season precipitation is more important.

Agriculture

Agricultural conditions vary throughout the region. In the highlands the soil ismorainic,and the hill slopes are cut by the locals into successive steps or terraces only a few meters broad, thus preventing water run-off and allowing spring crops to thrive. The region's economy relied mostly onshifting cultivationagriculture, supplemented by hunting, fishing and barter trade. Agricultural does not produce sufficient yields to meet local needs. The region's economy remained stagnant and atsubsistencelevels for centuries due to the lack of capital, investor access, or entrepreneurial knowledge. Inhabitants also relied heavily on wild and semi-cultivated species for food and herbal medicines.

Political divisions

The Eastern Himalayas consist of 6 distinct political/national territories:

• NepaliHimalaya (central, eastern and southern Nepal)
• Darjeeling Sub-Himalaya
• Sikkim (Indian)Himalaya
• AssamSub-Himalaya
• BhutanHimalaya
• Arunachal PradeshHimalaya
• Garhwal/KumaonHimalaya

Wildlife

Theblue poppy(Meconopsis gakyidiana) is the national flower of Bhutan

The Eastern Himalayas sustain a diverse array of wildlife, including many rare species of fauna and flora.Wildlife in Nepalincludessnow leopardin its Himalayan region, andIndian rhinoceros,Asian elephantandwater buffaloin the foothills of the Himalayas, making the country one of the world's greatestbiodiversity hotspots.Three major river basins of Nepal, namely theGhaghara,Gandaki RiverandKoshi Riverbasins, feature dense forests and provide habitat forbutterflyspecies and 8% of the world's bird species. Preserving this diverse wilderness is essential for the area's and the world's biodiversity. The area has many ecological projects intended to ensure the survival and growth of many species.

The most diversecloud forestis in India and China at 2,000–3,300 m (6,600–10,800 ft), andtropical rainforeston the lower slopes up to 900 m (3,000 ft) in the foothills. At higher elevations, wetpáramograsslands occur up to 4,500 m (14,800 ft), and above this elevation snow and ice occupies the space.Asian black bear,Himalayan vulture,andpikasare common at higher elevations, and also on the Tibetan plateau.Arunachal macaque(Macaca arunachalensis) andRhesus macaque(M. mulatta) live in the tropical cloud forests, alongside varioussunbirdandpheasantspecies. Himalayan high-elevation wetlands are also notable for their biodiversity.

Meconopsis gakyidianais the national flower of Bhutan, commonly called the blue poppy. This flower was the source of an ecological mystery for nearly a century, due to its misclassification asMeconopsis grandis.In 2017, after three years of field work and taxonomic studies, its classification was corrected by Bhutanese and Japanese researchers. It was theorised this misclassification may have arisen due to the finding that some Himalayan flora readilyhybridizewith each other and produce viable seeds, causing wider morphological diversity.

See also

• Western Himalaya
• Indus-Yarlung suture zone
• Main Himalayan Thrust
• Lower Himalayan Range
• Ecology of the Himalayas
• Geology of the Himalaya
• Sivalik Hills
• Geography of Myanmar
• Eastern South Asia
• Indian Himalayan Region
• Jammu and Kashmir (union territory)
• Transhimalaya
• Indo-Gangetic Plain

External links

• Eastern Himalayas– World Wildlife Fund projects