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Vol. 12(10), pp. 8-16The McAllen International Orchid Society JournalOctober 2011

A Geospatial approach to Diversity of Cymbidium Swartz in Sikkim

D. Barman,1 R.P. Medhi,2 Utpala Parthasarathy,3* K. Jayarajan,4 and V.A. Parthasarathy5

1,2 NRC for Orchids, Pakyong, E. Sikkim 737106, India
3,4,5 Indian Institute of Spices Research, P.B. No.1701, Marikunnu, Calicut 673012, India
* author to whom correspondence is addressed

Abstract

Cymbidium Swartz, commonly known as the boat orchid, is found in the forest areas of Sikkim. The majority of species of this genus in India are located in the Eastern Himalayas. Seventeen species of Cymbidium have been collected from the 132 sites of Sikkim. A geographic information system (GIS) study was done with the environmental parameters of rainfall, temperature and altitude, and their relation to the distribution of the species. The species diversity and richness was studied with point to point grid analysis of DIVA GIS. The results indicated that altitude and rainfall are the most important factors influencing the distribution of Cymbidium species. High richness was found in the altitude between 1500-2000 MSL. 1500-3000mm. precipitation is optimum for high concentration and diversity of the species.

Keywords

Diversity, Cymbidium, GIS, terrestrial, epiphytic, lithophytic

Introduction

Biodiversity is the variation of life forms within a given ecosystem. Destruction of the natural habitat is causing the extinction of the innate species. To control this damage it is important to increase the knowledge about the diversity and richness of the species. Species richness is the number of different species in a given area and the species diversity is an index that incorporates the number of species in an area and also their relative abundance. Diversity can be either inter- or intra- species.

A Geographic Information System (GIS) is the best tool to study species richness and diversity. The holistic understanding of the complex mechanisms that control biodiversity, as well as their spatial and temporal dynamics, requires synergetic adoption of measurement approaches. Sampling designs and related technologies could be improved with the use of Global Positioning System (GPS). Integrative tools such as GIS, GPS, and DIVA GIS are important complimentary systems for spatial studies (M.S.R. Murthy 2003).

Sampling of geographically distinct populations is a practical approach to understand biodiversity. Franke & Bennet, (1970) have considered this as the "cardinal principle" of the acquisition of crop genetic resources. The analysis of spatial information with GIS tools introduce new strategies for understanding and exploiting patterns of geographic diversity, and can be carried out efficiently with personal computers and GIS software. A GIS map can combine many layers of information to give a full view of the area or the crop concern. GIS makes it possible to link, or integrate, information that is difficult to associate through any other means. Thus, a GIS can use combinations of mapped variables to build and analyze new variables. Utpala et al. (2006) using DIVA GIS software found the hot spots of Piperia species richness at Western Ghats, in addition to the spatial analysis for Piperia species distribution in India. DIVA GIS is a software developed by International Potato Center, Lima, Peru. It is 'a geographic information system for the analysis of biodiversity data' (Hijmans et al. 2003).

The Orchidaceae is a large family with intensive genetic exploration According to Brieger (1975), the extreme degree of morphological variability is attributed to genetic drift in orchids. The genetic diversity evolves due to interactions among same species and sometimes with other subspecies.

Fig. 1. Sikkim Himalayas. [Nepal West, Tibet (China) North, & Bhutan East]. Photo: DSC_4377; Sun-30Oct11.

The genus Cymbidium is one of the most popular and widely cultivated genera, with about 70 species ranging from terrestrial to epiphytic or lithophytic (Brieger 1975). Members are naturally distributed in Japan, China, Korea, India, Malaysia, Vietnam, Borneo, Nepal, Formosa (Taiwan), The Philippines, New Guinea and Australia (Bose et al. 1999). A revised classification of the genus and assessment of specific delimitation and nomenclature reoriented 52 species within the genus (Bhattacharjee and Das 2008). About 23 species are reported from India. In India, most of the species are concentrated in Eastern Himalayas (David and Phillip 2007). Seventeen species were recorded in Sikkim Himalayas (Fig. 1) of which some are rare or extinct (Hegde 2000).

Cymbidium plants are sympodial and grow to a height of 60 cm. Plants bear long, narrow flag-like foliage and produce racemes as high as 60 cm, with arching sprays, and coloured waxy flowers. The plant stems are short, rarely elongated and pseudobulbs are ovoid. The scape is loosely sheathed, with flowers often large in a sub-erect or dropping raceme. The attractive range of colours for this genus include white, green, yellowish-green, cream, yellow, brown, pink and red. Sepals and petals are equal, show a diverse colour pattern, the lip is trilobed, column large, pollinia 2 to 4. Cymbidiums prefer a warm-cold temperature variation and flowering is generally not initiated at higher temperatures. Cymbidium species are mostly suited to a temperature range of 10°C and 25°C. A diurnal variation in temperature with a difference of 10°C between day and night is desirable for good health and bearing of flowers. Cymbidium species prefer partial light condition as members grow mostly on trees or in soils of forest areas. The genus prefers a range of 3500-8000 ft candles of light for growth and flowering (Chowdhery 1998).

The climate of Sikkim ranges from subtropical in the south to alpine in the north region. Most of the inhabited region of Sikkim witnesses a temperate climate with the temperature rarely exceeding 28°C in summer or dropping below 0°C in winter. The average annual temperature for most of Sikkim is around 18°C. The average rainfall is about 3000 mm and rainy season is from June to September.

In order to study the habitat requirement of Cymbidium species and to facilitate locations, this study, using a geographic information system (GIS), was carried out to construct a spatial habitat model of members. GIS habitat models have been successfully demonstrated to be powerful, cost effective tools for identifying the potential habitats of animals (Scepan et al. 1987). However, GIS models for individual plant species are less common (Cherril etal 1995).

Materials and Methods

Fig. 2. Cymbidium species distribution in Sikkim.

A systematic survey was done in the four districts (East, West, North and South districts) of Sikkim (Fig. 2). Seventeen Cymbidium species were collected from 132 locations. The species occurrences were plotted in the digitized map of Sikkim with the help of longitude and latitude using DIVA GIS (Hijmans et al. 2001). Longitude and latitude of the collection places were collected with the help of GPS at the time of collection. Species diversity and richness were studied from point to grid analysis option of DIVA GIS. The rainfall and altitude map of the state was prepared with BIOCLIM model of DIVA GIS (Hijmans et al. 2003). Using the Domain model, the niches of Cymbidium species were predicted.

Results

The species plotted with the longitude and latitude of the collection sites (Fig. 2) shows that C. aloifolium is the most common species present in throughout Sikkim. Most of the Cymbidium plants occur at subtropical altitude of 1000 to 2000 m. C. dayanum, C. munroanum and C. pendulum were also located in this altitude zone but were not found in higher altitudes.

Fig. 3. Altitude Grid of Sikkim.

C. dayanum was found in the East district at 800 to 1000 m. C. munroanum is a rare terrestrial species and was recorded in West district at a altitude of 700 to 900 m. However C. pendulum occur commonly throughout the state except in the higher altitude of north district, at a wide range of altitude from 300 to 1600 m. The annual rainfall at both zones ranges between 2500 and 5000 mm. The humidity is usually between 90% and 100% and the maximum temperature ranges from 30° to 35°C during summer in the tropical forest area. The winter temperature ranges between 20° and 25°C. The forests are multistoried. This type of tree combination with their close canopies form a dense, dark-humid environment which provides an ideal habitat to support the luxuriant growth of epiphytic orchids like C. aloifolium and C. pendulum (Lucksom 1997). C. cochleare and, C. cyperifolium occur at an altitude of 1000 to 2000 m. C. cyperifolium, a rare and threatened species with a terrestrial habitat, was prevalent in West District. It was located in one place of the North District at a altitude of 1600 to 1900 m (Fig. 3).

Fig. 4. Precipitation map of Sikkim.

C. devonianum was found at an altitude range of 1200 to 2100 m. Other species such as C. eburneum, C. erythraeum, C. lancifolium, C. mastersii and C. whiteae were also found in this altitude range. C. eburneum is a threatened species, rarely found in North and West Districts at an altitude range of 1400 to 1700 m. The habitat of C. lancifolium is terrestrial while C. erythraeum is epiphytic. Both occur at an altitude range of 1400 to 2000 m. C. whiteae, (an endemic species) and C. mastersii were collected from East District at 1500 to 1700 m. At this altitude range summer precipitation is heavy (2500 to 5000mm), the day temperature is between 25° and 30°C and the night temperature drops down below 20°C, depending on the altitudinal variation (Fig. 4). Here the trees are shorter and bushy and make the undergrowth of forest thicker (Hegde 2000). C. eburneum was found in partially exposed areas while C. devonianum occurred in densely shaded areas (Brieger 1975). The forest floor is rich in humus and supports the growth of C. longifolium and C. iridioides. C. iridioides , a rare and threatened species was collected from the East District at a range of 700 to 1600 m. C. longifolium, C. gammieanum and C. hookerianum occur at an altitude range of 1300 to 3200 m. It indicates that these species are subtropical to temperate and sub-temperate. The temperature of temperate and sub-temperate zone varies around 10°C and seldom exceeds 20°C. Severe winters with occasional winter snows, along with scanty rainfall during January and February, with the presence of heavy fog and mist and heavy summer rains are characteristic features of this zone. Very few species were found in these types of climatic conditions and locations. However, C. hookerianum and C. mastersii were collected under these climatic conditions.

Fig. 5. Map showing hot spot of species richness of Cymbidium species.

Species richness studied with a 10 km grid reveals that southern part of North Sikkim and northwestern part of East Sikkim has the highest richness (Fig. 5).

The eastern part of West District also shows the highest richness with 7 to 10 species. East 88°49' to 88°60', North 27°29' to 27°49'  and East 88°50' to 88°60', North 27°30' to 27°39' to East 88°20' to 88°30' is having the highest richness. The map shows low altitude (1500 to 2000 m) and high rainfall (2000 to 3000 mm) and an annual average temperature ranging from 10°C to 20°C which is suitable for richness of Cymbidium species. Species richness is the number of species available in a particular area in this study is 10 km2 area. It is also known as a hot spot of species richness. High richness was found in the altitude zone between 1500 and 2000 m while the precipitation of the hot spot of richness is 1500-3000mm. The result indicated that the altitude and rainfall are the most important factors influencing the distribution of Cymbidium species. Utpala et al. (2006a, 2006b) obtained similar findings in case of Piperia species diversity.

Fig. 6. Map showing diversity index of Cymbidium species.

A diversity index gives the density of the species. In the present study two patches are found which have a high diversity index. The area of high diversity occurs in between 27°30' and 27°50' North and 88°50' to 88°70' E, in the southern part of North Sikkim and the northwestern part of East Sikkim which have species including C. devonianum, C. longifolium, C. cochleare and C. cyperifolium. Another high diversity region is located in the eastern part of West district, between 27°21' to 27°40' North and 88°20' to 88°30' East. The species there are almost the same ones as above. It shows that C. devonianum, C. longifolium, C. cochleare and C. cyperifolium are the species which are available in large concentration in Sikkim (Fig. 6).

Fig. 7. Domain map showing suitability of Cymbidium species.

It is interesting to note that the richness grid falls within the diversity grid, but in a lesser area. This study gives a clear idea of the presence of Cymbidium species in Sikkim. With the help of the climatic envelope of the collection sites a prediction map of cymbidium availability in India was prepared (Fig. 7).

The model indicates that the domain of Cymbidium is in the North Eastern Himalayan states only. The map shows 90 to 100% domain in Sikkim, 80-90% in parts of North Bengal, Meghalaya and Arunachal while 70-80% domain could be in Mizoram, Tripura, Manipur and parts of Nagaland, Meghalaya and Assam. Orissa, West Bengal parts of Bihar, UP, Andhra Pradesh could be marginally suitable while other parts of India are not suitable for Cymbidium domain.

Conclusions

The genus Cymbidium has great horticultural importance with a growing demand in the orchid trade. At present, superb hybrids of Cymbidium with outstanding colour and longer keeping quality are available, and many of the species of this genus available in India have desirable characters for developing superior hybrids.

The collection data gives an idea of the diversity as well as the richness area. When the species are fallen in the richness grid, the authorities should take particular attention to conserve those species which are not in a very high concentration. GIS provides a tool to manage and monitor the spatial relationships of various components making up the stratification such as species distribution pattern, plant associations, bio-geo-climatic variables, forest and soil types. A lack of primary biological data for construction of species richness maps, less expertise of modeling for species richness maps based on ecological factors, and a lack of awareness of GIS application etc. are some of the constraints, which need to be rectified at various levels.

Acknowledgements

The authors are grateful to Dr. P.N. Mathur, Coordinator, Biodiversity International, New Delhi for help.

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Copyright © 2011 D. Barman, R.P. Medhi, Utpala Parthasarathy, K. Jayarajan, and V.A. Parthasarathy