Rhododendrons in Indian Himalayan Region : Diversity and Conservation

The genus Rhododendron of Indian Himalayan Region (IHR) has been enumerated in the present paper. A total of 87 species, 12 subspecies and 8 varieties of Rhododendrons recorded in IHR, among these 6 species and one subspecies are reported from Western Himalaya. The maximum concentration of 86% observed in Arunachal Pradesh (75 species). The species of Rhododendrons exhibit significant diversity in habit and broad range of distribution from the altitude of 800-6000 m. and the best range is observed in 3001-3500 m altitudes. In analysis revealed 20 taxa are endemic, 30 are rare, 24 are threatened / endangered, 3 are vulnerable and 47 taxa have to be assessed. The major threats to rhododendrons are deforestation and unsustainable extraction for firewood and incense by local people has been discussed.


Introduction
The genus Rhododendron, family Ericaceae, was founded by Linnaeus [1].The word Rhododendron is derived from two Greek words rhodon (rose) and dendron (tree) meaning rose tree.The genus with attractive and beautyful flowers is represented by 850 species in the world [2].They are mostly distributed at higher elevations in the Sino-Himalayan region with maximum concentration in Western China [3].In India, the species are mostly confined to the Himalayan region, particularly in Eastern Himalaya.A revision of the genus was carried out by Cullen [4], Chamberlain [5], Philipson and Philipson [6], Chamberlain and Rae [7], Kron [8] and, Judd and Kron [9].Preliminary enumerations and inventories of the genus were made by Pradhan [3,10], Ghosh and Samaddar [11], Bhattacharyya and Sanjappa [12].Sastry and Hajra [13] and Mao et al. [14] were made the contribution on rare and endemic Rhododendrons of India.The Rhododendrons of Sikkim-Himalaya region were done by Pradhan and Lachungpa [15] and Singh et al. [16].The importance of Rhododendrons in Meghalaya dealt by Yumnam [17].
The Indian Himalayan Region (IHR) occupies a special place in the mountain ecosystems of the world.The IHR is one of the most fragile mountain regions of the world and holds an enormous repository of biological diversity which is increasingly under pressure from human activities.The region comprises a rich variety of flora, fauna, human communities and culture.Of the estimated 8,000 species of vascular plants in the Himalayan region, around 3,160 are endemic and 450 species are endangered [18,19].The indiscriminate exploitation, destruction of habitats, spread of harmful chemicals and introduction of alien species, a number of plants have been disappeared while others await a smilar fate [20].As a result, gap between demand and supply is widening.In this regards, global efforts are being made to conserve the phytodiversity especially rare, endangered and threatened species, which are known to be important component of biodiversity.
Due to human interference the natural populations of rhododendrons in the entire Himalaya are gradually diminishing.The major threats to rhododendrons are deforestation and unsustainable extraction for firewood and incense by local people.A set of rhododendrons which are classified as rare/endangered may be wiped out from the biota in the near future if proper conservation measures are not made.So, the present task of diversity and conservation status of Rhododendrons of Indian Himalayan Region has made.

Methodology
The present work on Rhododendrons of Indian Himalaya is based on extensive literature surveys made in different states of Indian Himalayan Region (IHR).For the threat categories, we have consulted different published scientific papers, monographs, red-list documents, IUCN list, etc.All the taxa have been listed alphabetically with altitude, distribution in Indian Himalayan States and other region, and revealed threat categories.For enumeration of species, the IHR is divided into two botanical regions, namely the Western Himlaya and the Eastern Himalaya.The Western Himalaya region is the states of Jammu & Kashmir, Himachal Pradesh and Uttaranchal.Similarly, the Eastern Himalayan region includes the seven sisters states of North-Eastern India (Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura), Sikkim and Darjeeling district of West Bengal.The species of Rhododendrons are calculated and enumerated in state wise representation of Western and Eastern Himalaya.

Results
A total of 87 species, 12 subspecies and 8 varieties of Rhododendrons recorded in IHR (Table 1).The Western Himalaya has 6 species, namely Rhododendron anthopogon (Plate 1a), R. arboreum (Plate 1b), R. barbatum, R. campanulatum (Plate 1c), R. lepidotum and R. nivale; while Eastern Himalaya is represented by all enumerated species.The maximum concentration of species is observed in Arunachal Pradesh (86%).Out of 87 species known from IHR, 75 species occur in the state of Arunachal Pradesh alone.The state wise distribution of species is showed in Figure 1.The distribution of species in relation to altitude is shown in Figure 2. The maximum numbers of Rhododenrons are present in the 3001-3500 m altitudes, lowest in 500-1000 m and above 5000 m, and absent in less than 500 m (Figure 2).A single species namely R. arboreum Sm. is only found in less then 1000 m altitude (from 800 m onwards) and found in almost all the states of IHR except Assam and Tripura.R. nivale Hook.f. is a single species found in above 5000m altitude and found in the state of Sikkim and Uttarakhand

Discussion
The species of Rhododendrons exhibit significant diversity in habit and broad range of distribution from the altitude of 800-6000 m.A total of 87 species, 12 subspecies and 8 varieties of Rhododendrons recorded in IHR.
Out of these species, 20 taxa are endemic to IHR.While considering the status, 47 taxa are not yet evaluated, 30 are rare, 24 are threatened / endangered and 3 are vulnerable [14,16,21].In comparison with neighboring countries, China is having a total of 571 species of Rhododendrons, out of which 409 species are endemic [22] and other countries like Pakistan, Bhutan, Nepal, etc are having very less species diversity in Rhododendrons.A lot of exploration is still lacking to discover the species described in other parts of the country, because, the China and India is having similar habitat in support the growth of Rhododendrons.While considering the importance of altitude the maximum number of Rhododen-drons present in the altitudes of 3001-3500 m.These altitudes are considered as best suitable sites for Rhododendrons for conservation and multiplication.
In the recent days, IHR is greatly affected due to various threat posed by the nature as well as by human beings.Since Rhododendrons are the inhabitants of the IHR, they are also greatly affected and their population in the nature is gradually dwindling [14].The rise in population with demand on land for farming, increased animal husbandry practices, construction of roadways, hydel-power stations and allied works, army personnel garrisoned at alpine locations and lately the tourist influx have collectively resulted in the building up of considerable pressure on the availability of rhododendron species.The major threats to rhododendrons are deforestation and unsustainable extraction for firewood and incense by local people.Due to the presence of polyphenols and flavonoids, rhododendrons make excellent firewood that burns even under wet conditions.Rhododendron firewood is also being used in the high-altitude trekking corridor for the purpose of tourism.Some of the species have already become scarce, for example, R. leptocarpum is endangered and reported to have only 16 surviving individuals at present in the Sikkim [16].
The conservation of Rhododendron species can be effected by two well established means, the in-situ and exsitu methods.In-situ conservation can be brought about by establishing Rhododendron sanctuaries, Parks, etc.Some efforts by Sikkim forest department and Sikkim Rhododendron Society have been made by fencing the Rhododendron rich sites and declaring them as Rhododendron Sanctuary between Lachung and Yumthang in the State.Similar efforts need to be made by Arunachal Pradesh Government as the state is home for more than 50 percent rare and endemic IHR species.The ex-situ conservation can be effected by cultivating Rhododendron species in the gardens and parks under suitable climatic conditions or by using tissue culture techniques.There should not be many difficulties in introducing these species in Botanic Gardens and Parks as most of them have successfully been introduced and cultivated in the European and American countries.The species of Rhododendron arboreum are propagated through cuttings [23,24].Tissue culture studies of Indian Rhododendrons are recently initiated; only few species especially Rhododendron maddeni has only been propagated through tissue culture methods (Singh and Gurung, 2009) and some others are under progress.But in foreign countries, the Rhododendrons have already been carried out for commercial cultivation [26][27][28][29][30][31][32].The standard culture medium for tissue culture methods is readily available in the market [14].Successful tissue culture of these species will be a great contribution for rapid multiplication and towards in-vitro conservation.The success of conservation programme depends on the awareness of local people.It is imperative to educate the local inhabitants about the wealth of Rhododendrons and importance towards the conservation of biodiversity in IHR.

Figure 1 .Figure 2 .
Figure 1.Distribution of rhododendrons in different states of IHR.