JARS v64n4 - Diversity and Distribution of Rhododendrons in Arunachal Himalaya, India

Diversity and Distribution of Rhododendrons in Arunachal Himalaya, India
Ashish Paul, Mohamed Latif Khan, Ashesh Kumar Das and Pijush Kumar Dutta

Abstract
Rhododendron is one of the important dominant plant groups in the temperate, subalpine and alpine regions of western Arunachal Pradesh, India. The main aim of this study is to document Rhododendron biodiversity and conservation in western Arunachal Pradesh. The study area is the West Kameng and Tawang districts of Arunachal Pradesh, where extensive field surveys were made on a bimonthly basis. A total of 47 Rhododendron taxa were recorded from these two districts, which cover 16.4% of the geographic area of the state, from a total of 90 reported from all of Arunachal Pradesh. Sizes of different taxa ranged from tiny shrubs to large trees, and a majority belonged to the subgenus Hymenanthes . We document three species as new to Arunachal Pradesh, and 13 species are endemic, endangered, rare or threatened. Maximum diversity of Rhododendron was observed between 2000 to 4000 m (6560–13,125 feet)elevation. Rhododendron formed a dominant vegetation type, comprising a fragile ecosystem in the timberline zone that included other plants and animals over this altitudinal gradient. Thus, we consider Rhododendron a keystone plant in the western part of Arunachal Pradesh.

Introduction
Rhododendron is a relatively primitive group of flowering plants that have flourished in the temperate zones of the northern hemisphere for almost 100 million years (de Milleville, 2002). Towards the equator, this genus is mainly distributed at higher altitudes, and today some species have significant ecological and economic importance (Mao et al ., 2001). Species heights range from 2.5 cm (1 inch) alpine plants to 30 m (98 feet) tall trees and are either evergreen, semi deciduous or deciduous (Hora, 1981). The genus is divided into eight subgenera (Chamberlain et al ., 1996).

Rhododendron has the greatest number of species of all genera in the family Ericaceae, with more than 850 species. It is distributed throughout northeast Asia and Eurasia, Western Europe and North America (Chamberlain et al ., 1996). The genus covers a vast area of southeastern Asia stretching from the northwestern Himalayas through Nepal, northeastern India, eastern Tibet, northern Burma, Bhutan, western and central China and south through Thailand, Vietnam, Malaysia, Indonesia, the Philippine Islands, Papua New Guinea to Australia. About 20% of the world's Rhododendron species occur in the Himalaya; 35% in the Philippines, Indonesia, Malaysia, and other islands; 30% in China and Vietnam; 5% in Japan and 10% in America and Europe (Kenneth Cox, pers. comm.). Species diversity of the genus is rich throughout the Himalayan region into the Chinese provinces of Sichuan and Yunnan. The aesthetic values of rhododendrons are significant and it is the recognized regional flower in the American States of Washington ( Rhododendron macrophyllum ) and West Virginia ( Rhododendron maximum ) and in Japan's Shiga Prefecture ( Rhododendron metternichii var. hondoense ), and Rhododendron arboreum is Nepal's national flower and is depicted on its coat of arms (de Milleville, 2002). In India, Rhododendron is the state flower of Himachal Pradesh ( Rhododendron campanulatum ) and Nagaland ( Rhododendron arboreum ), and is the state tree of both Sikkim ( Rhododendron niveum ) and Uttarakhand ( Rhododendron arboreum ) (Kant, 2004; Joshi and Sharma, 2005).

Apart from their aesthetic, sacred and ethnomedicinal values, several species have commercial and social importance (Leach, 1986). There are about 111 Rhododendron species on the Indian subcontinent (Mao et al ., 2001), with a majority of them in the state of Arunachal Pradesh in the Eastern Himalayas. This region is a global biodiversity hotspot (Myers et al ., 2000) and is recognised as one of 200 globally important ecoregions (Olson and Dinerstein, 1998). Kaul and Haridasan (1987) classified the vegetation of Arunachal Pradesh into six broad forest types, tropical, subtropical, temperate, sub-alpine, alpine and secondary forests, and rhododendrons occur in subtropical, temperate, sub-alpine and alpine areas. Different species have different altitudinal distributions and Rhododendron forests occur in some areas. However, western Arunachal Pradesh is relatively poorly explored, and so it was there that we conducted surveys for rhododendrons.

Materials and Methods
Extensive exploration trips were carried out on a bimonthly basis in the West Kameng and Tawang districts of western Arunachal Pradesh. Specimens of rhododendrons were collected and data were recorded for each species on habit, habitat, geographic location and occupied environmental niches. Herbarium specimens were prepared following the protocol of Jain and Rao (1977). Each species was identified by consulting available flora references, including The Rhododendrons of Sikkim-Himalaya (Hooker, 1849), Sikkim-Himalayan Rhododendrons (Pradhan and Lachungpa, 1990), Encyclopedia of Rhododendron Species (Cox and Cox, 1997), The Rhododendrons of Nepal (de Milleville, 2002), Flowers of the Himalaya (Polunin and Staninton, 2006), Materials Flora of Arunachal Pradesh (Giri et al ., 2008) and Flora of Assam (Kanjilal et al ., 1939). Several herbaria, such as the State Forest Research Institute (SFRI) Itanagar, Botanical Survey of India (BSI) Itanagar, and Shillong and Central National Herbarium (CNH) Kolkata, were also consulted for validation of identifications, and further validation was done by consultation with Rhododendron taxonomists Mr. Kenneth Cox (Managing Director, Glendoick Gardens Ltd., Perth, Scotland) and Dr. D. Bhattacharjee (Rhododendron revisioner, Botanical Survey of India, Kolkata). Conservation categories of collected Rhododendron species were assigned according to Mao et al ., (2001)

Results
A total of 47 taxa (38 species, 4 subspecies and 5 varieties) were recorded during our surveys in West Kameng and Tawang districts of Arunachal Pradesh (Note: specific locations for each species can be obtained from the author or the JARS editor). Of these, seven rhododendrons, i.e., R. x candelabrum (hybrid of R. thomsonii x unknown), R. ciliatum , R. x sikkimense (hybrid of R. thomsonii x unknown), R. bhutanense , R. flinckii , R. kesangiae , and R. kesangiae var. album (Figure 1a, b, c, d, e, f) were recorded from the explored area, the first three being reported for the first time from Arunachal Pradesh. Only two Rhododendron subgenera, i.e., Hymenanthes and Rhododendron , were observed, although species of two other subgenera, Tsutsusi ( R. arunachalense ) and Azaleastrum ( R. moulmainense ), have been previously documented from this state. Most of the observed species (62%) belonged to Hymenanthes , and 38% belonged to Rhododendron . The sizes of collected taxa ranged from small shrubs to large trees and epiphytes. Out of 47 taxa recorded, 28 were shrubs or small trees, nine were large trees, seven were epiphytic shrubs, two were dwarf shrubs and one was a bushy shrub. Out of the total recorded Rhododendron , 13 taxa are endemic, endangered, rare or threatened in India, and two are endemic only to Arunachal Pradesh ( R. arboreum ssp. delavayi var. peramoenum and R. coxianum ). We found three new Rhododendron taxa to Arunachal Pradesh (Table 1: R. x candelabrum , R. ciliatum , and R. x sikkimense ).

Table 1. Endemic, endangered, rare, threatened and new Rhododendron taxa recorded from different localities of West Kameng and Tawang districts of Arunachal Pradesh (AP).
Botanical name	Endemic	Endangered	Rare	Threatened	New Record
Rhododendron arboreum ssp. delavayi var. peramoenum	+ (AP)	-	-	-	-
Rhododendron x candelabrum	-	-	-	-	+
Rhododendron ciliatum	-	-	-	-	+
Rhododendron coxianum	+ (AP)	-	-	-	-
Rhododendron dalhousiae var. rhabdotum	-	-	+	-	-
Rhododendron edgeworthii	-	-	+	-	-
Rhododendron falconeri ssp. eximium	-	+	-	-	-
Rhododendron hookeri	-	-	+	-	-
Rhododendron kendrickii	-	-	+	-	-
Rhododendron keysii	-	-	+	-	-
Rhododendron maddenii	-	-	+	-	-
Rhododendron megeratum	-	-	+	-	-
Rhododendron neriiflorum ssp. phaedropum	-	-	-	+	-
Rhododendron pendulum	-	-	+	-	-
Rhododendron x sikkimense	-	-	-	-	+
Rhododendron tanastylum	-	-	+	-	-

Maximum species diversity of rhododendrons along an altitudinal gradient was observed between 2000 to 4000 m. R. arboreum ssp. arboreum was found widely distributed between 1500 to 3500 m (4925 to 11,485 feet)and R. coxianum from 1500 to 2000 m (4925–6965 feet) (Figure 2). Most of the endangered, threatened, rare, and endemic taxa were distributed between 1500 to 4000 m, while the newly recorded taxa were distributed between 3000 to 4000 m. Thirty taxa were recorded between 3000-3500 m, 24 taxa between 2500-3000 m and only five taxa were recorded between 1500-2000 m (Table 2).

Figure 2. Distribution of rhododendrons along an altitudinal gradient in West Kameng and Tawang districts of Arunachal Pradesh. (Black = present)
Botanical name	Altitude (m masl)
	1500 – 2000	2000–2500	2500–3000	3000–3500	3500–4000	4000–4500
R. anthopogon
R. arboreum
R. arboreum ssp. arboreum
R. arboreum ssp. cinnamomeum
R. arboreum ssp. delavayi var. delavayi
R. arboreum ssp. delavayi var. peramoenum
R. barbatum
R. bhutanense
R. camelliiflorum
R. campanulatum
R. campylocarpum
R. x candelabrum
R. ciliatum
R. cinnabarinum
R. coxianum
R. dalhousiae
R. dalhousiae var. rhabdotum
R. edgeworthii
R. falconeri
R. falconeri ssp. eximium
R. flinckii
R. fulgens
R. glaucophyllum var. tubiforme
R. grande
R. griffithianum
R. hodgsonii
R. hookeri
R. kendrickii
R. kesangiae
R. kesangiae var. album
R. keysii
R. lanatum
R. lepidotum
R. lindleyi
R. maddenii
R. megeratum
R. neriiflorum ssp. phaedropum
R. niveum
R. pendulum
R. setosum
R . x sikkimense
R. tanastylum
R. thomsonii
R. triflorum
R. virgatum
R. wallichii
R. wightii

Table 2. Number of Rhododendron taxa along with altitudinal gradient in western Arunachal Pradesh.
Altitude		Number of taxa
(m)	(ft)
1500 – 2000	4925–6965	5
2000 – 2500	6965–8200	15
2500 – 3000	8200–9840	24
3000 – 3500	9840–11,485	30
3500 – 4000	11,485–13,125	18
4000 – 4500	13,125–14,760	6

Discussion Our study revealed the occurrence and locations of many Rhododendron from the West Kameng and Tawang districts of Arunachal Pradesh. Though the two districts cover only 16.4% of the state's geographical area and 16.8% of the state's total forest cover (FSC, 2005), more than 50% of the earlier reported taxa (Mao et al., 2001) were recorded from these districts. During a preliminary survey, Paul et al ., (2005) reported the occurrence of 20 Rhododendron taxa from western Arunachal Pradesh, and 89% of the species reported from Sikkim Himalaya (Pradhan and Lachungpa, 1990; Singh et al ., 2003; Tiwari and Chauhan, 2005, 2006) have been encountered in western Arunachal Pradesh.

Two species, R. x candelabrum , and R. x sikkimense , were previously reported to be endemic to Sikkim (Pradhan and Lachungpa, 1990; Tiwari and Chauhan, 2005), but are now know to also occur in Arunachal Pradesh. R. ciliatum , previously reported only from Sikkim, Nepal, Bhutan and Tibet (Pradhan and Lachungpa, 1990; Cox and Cox, 1997); and another four taxa, R. bhutanense , R. flinckii , R. kesangiae and R. kesangiae var. album , previously reported to be endemic to Bhutan (Cox and Cox, 1997), were also found in our study area, as previously documented by Cox (2005, 2007). Among the recorded Rhododendron , 14 taxa (30%; R. arboreum ssp. delavayi var. peramoenum , R. bhutanense , R. coxianum , R. dalhousiae var. rhabdotum , R. falconeri ssp. eximium , R. flinckii , R. glaucophyllum var. tubif orme , R. hookeri , R. kesangiae , R. kesangiae , var. album , R. kendrickii , R. megeratum , R. neriiflorum ssp. phaedropum and R. tanastylum ) have only been reported in Arunachal Pradesh in India. Twelve taxa are common both in Arunachal Pradesh and Sikkim (26%), 11 taxa are found in Arunachal Pradesh, Sikkim and West Bengal (23%), and the other ten taxa found in Arunachal Pradesh are found in other parts of India (21%) (Pradhan and Lachungpa, 1990; Mao et al ., 2001).

Rhododendron is abundantly distributed in the temperate, subalpine and alpine regions of western Arunachal Pradesh. Reports by several researchers emphasize that many species of Indian Rhododendron are concentrated in the Arunachal Himalaya (Sastry and Hajra, 1983; Ghosh and Samaddar, 1989). The state is recognized as a significant Himalayan biodiversity hotspot, as it has a varied climate, an annual rainfall of 2000–8000 mm, and a wide range of elevation (100–7000 m; 328 to 22,965 feet). Moreover, western Arunachal Pradesh is terrestrially connected with neighbouring countries such as China and Bhutan, which have a rich diversity of Rhododendron . As a result, there is the possibility of floral range extension throughout this Southeast Asian region. Favourable soil physicochemical characteristics and geology have likely influenced the diversity of rhododendrons in this mountainous region. The present findings also showed that more than 50% Rhododendron taxa of the Arunachal Himalaya occur in western Arunachal Pradesh. Therefore, this part of the state should be considered important in the conservation of rhododendrons in India.

However, the reality is that in Arunachal Pradesh, rhododendrons and their habitats are facing tremendous threats, both natural and anthropogenic. Natural disturbances like landslides (Figure 3a) and wash out of smaller patches by runoff are frequent. Major anthropogenic impacts are uncontrolled and indiscriminate harvesting for fuelwood (Figure 3b), mainly for the purpose of cooking and room heating. Agricultural activities, grazing, clear-felling and subsequent forest fires are also prominent. These activities may cause significant decline in populations and species diversity of rhododendrons in Arunachal Pradesh. A worst case scenario is that more species will become endangered, rare and threatened in the future.

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Acknowledgements
This work was supported by a research grant from Council of Scientific and Industrial Research (CSIR), New Delhi (38(1052)/02/EMR-II) to the Forestry Department, NERIST, Nirjuli (Itanagar) and Seicho-no-ie through WWF-Japan and WWF-International to WWF-India. The authors thank officials of Forest Department, Government of Arunachal Pradesh, village headmen (Gaon Burahs) local guides and the local people for cooperation and support during the field survey. The authors also thank Mr. Kenneth Cox for invaluable suggestions during the preparation of the final manuscript. Thanks also due to Mr. Kenneth Cox, Dr. K. Haridasan and Dr. Debojit Bhattacharjee for helping in the identification of Rhododendron species. Thanks to Mr. Bijit Basumatary for help during the field survey. Also thanks to WWF-India Officials from Field Office, Itanagar and Delhi Secretariat for all necessary support and cooperation.

Note : If desired, the author can be contacted to obtain the localities in the West Kameng and Tawang districts of Arunachal Pradesh where the different species of rhododendrons were found.