Bhutan - Lindsay Brown [64]
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Conservation International’s website on biodiversity (www.biodiversityhotspots.org) includes facts and figures on biodiversity in the Himalaya hotspot, including Bhutan. Although these hotspots collectively occupy 2.5% of the earth’s space, they are home to 50% of the world’s plant species and 42% of the world’s vertebrates.
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THE DUARS
The fertile valleys that extend 15km to 30km from the hills to the Indian states of Assam and Bengal are known as the duars, as is the lower portion of Bhutan’s foothills. Duar is a Sanskrit word meaning ‘passes’ or ‘gates’, and is the origin of the English ‘door’. Before the British annexed Bhutan’s southern regions each duar was under the control of a Bhutanese dzongpen (lord of the dzong), but as they were malaria-infested they were largely unoccupied by the Bhutanese, who stayed in the northern hills.
Each duar is named after a river valley that leads out of Bhutan, though the duar itself is actually the land between two rivers. The land ranges from an elevation of about 100m to almost sea level at the Brahmaputra River, and the slope is barely perceptible. The fertile land now supports tea gardens, rice paddies and a few protected areas such as the Buxa Tiger Reserve.
Seven of the duars abut the border of Assam between the Dhansiri (Durlah) and Manas Rivers. The remaining 11, from the Manas River to the Teesta River in the east, border on the state of West Bengal.
Rivers
Rivers, or chhus, play an important role in Bhutan’s geography, and their enormous potential for hydroelectric power has helped shape the economy. Flowing south, they have created deep valleys, making all east–west travel a tedious process of steep winding descent followed by an equally steep, equally winding climb to the next ridge. There are four major river systems in Bhutan, most known by several names as they flow through the country.
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Wild Rhododendrons of Bhutan by Rebecca Pradhan is a beautiful guide to Bhutan’s rhododendrons, with photographs of all 46 species.
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Most of the rivers have their headwaters in the high mountains of Bhutan, but the Himalaya range is not a continental divide, and there are three rivers that actually flow through the mountains into the country. The Amo Chhu flows from Tibet’s Chumbi valley across the southwestern corner of Bhutan, where it becomes the Torsa Chhu, and exits at Phuentsholing. Two tributaries of the Manas, in eastern Bhutan, originate outside the country. The Kuri Chhu has its headwaters in Tibet (where it is known as the Lhobrak Chhu) and crosses into Bhutan at an elevation of only 1200m; the other tributary, the Gamri Chhu, rises in India’s Arunachal Pradesh.
The Thimphu Chhu, known in its lower reaches as the Wang Chhu, powers the Chhukha and Tala hydroelectric projects and eventually becomes the Raidak River in India. The Pho Chhu and Mo Chhu join at Punakha to form the Puna Tsang Chhu, which drains the area between the Dochu La and the Black Mountains. This river is known as the Sankosh when it reaches India. The Manas is Bhutan’s largest river, draining about two-thirds of the country; in its upper reaches it is known as the Drangme Chhu. The Mangde Chhu flows from Trongsa and joins the Manas Chhu just before it flows into India. Unlike most other rivers that flow from Bhutan into India, the Manas retains its name when it crosses the border. All of Bhutan’s rivers eventually flow through the duars to become part of the Brahmaputra, which is known in Tibet as the Yarlung Tsampo, with a source near Mt Kailash in the far west.
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The most authoritative and complete guide to Bhutan’s mammals, their identification, behaviour and distribution is A Field Guide to the Mammals of Bhutan by Tashi Wangchuk.
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Because the central Himalaya of Bhutan receives the full brunt of the monsoon, Bhutan’s rivers are larger and have created much broader valleys