A saussurea globosa plant in western Arunachal Pradesh. Picture by Pijush Kumar Dutta

Guwahati, Sept. 22: Four scientists of the Northeast have discovered rare plants indigenous to Nepal, Bhutan and China along the western Arunachal Pradesh timberline.

A timberline is an area of transition between forests and barren areas at high altitudes. Because of harsh climactic conditions, trees cannot grow after a certain altitude and hence, shrubs and herbs make up the forested area. “Such an area between two different types of ecosystems, known as an ecotone, is found to have high biodiversity. A timberline is also considered an indicator of global warming, since, with an increase in temperature, the line tends to shift to higher altitudes,” Pijush Dutta, one of the scientists, said.

Dutta, along with B.K. Dutta, R.C. Sundriyal and Ashesh Kumar Das, conducted the study between 2008 and 2011 in an area of 9,594 square km in West Kameng and Tawang districts of the hill state. Their findings have been reported in the current issue of Current Science. The team discovered 11 species of plants of which four are from Nepal, Bhutan, China and Sikkim with high conservation value for the first time in western Arunachal Pradesh. Primula poluninii (Nepal), rhododendron niveum (Bhutan and Sikkim), rhododendron sikkimense, saussurea yakla (Sikkim) and saussurea globossa (China) are some of the plants they discovered.

Of these 11, five — aconitum ferox, picrorhiza kurrooa, nardostachys grandiflora, saussurea obvallata and rheum nobile have medicinal value.

Saussurea globosa — the endemic plant form China — is a tall herb that grows to a height of around 10-70cm and is found in alpine areas. “The uppermost stem leaves are boat-shaped. Flowers are purple and like other saussurea species, the flowers of this plant are covered with thick hair that helps it survive the night frost and protects it from the ultra-violet radiation that increases with altitude,” Dutta said.

The timberline in the eastern Himalayas encompasses a large area in the two Arunachal Pradesh districts and is mostly distributed at altitudes ranging between 3,900 and 4,200 metres.

“More humid conditions in the eastern Himalayan timberline compared to the western Himalayas provide a more conducive environment for tree growth and, as a result, the upper limit of the timberline in this sector goes up to 4,570 metres, which is much higher compared to the timberline limit of 3,600 metres in the western Himalayan region,” Dutta said.

The scientists recorded 122 plant species from the timberline zone belonging to 29 families with 56 species being common to areas above and below the zone. “It is interesting to note that 77 per cent of the total recorded plants was found distributed within the Himalayan region, while 28 per cent was confined to the eastern Himalayas,” the paper said.

The study found the timberline to be one the most sensitive ecotones, but under tremendous biotic pressure for diverse needs.

“The pressures range from collection of firewood by herders and unregulated grazing at all sites. In Bhagajang, where the number of pilgrims visiting sacred lakes has increased after a road was constructed, collection pressure on available rhododendron species for firewood was found to be high. The construction of roads in Mandla and Bhagajang and maintenance and widening of roads at Sela and Nagula are also exerting pressure on the plants found in these areas,” the paper said.