The Orchid Diversity in Sikkim

According to J.Joseph the author of Orchids of Nilgiris, North East India forms the junction of immigratory elements from the neighboring regions like Tibet, China Burma and other regions. Another reason given is that the region falls in the tremor belt and according to the tremor theory (Joseph 1982) the electromagnetic and other forms of invisible energies, released by the occasional tremors, bombard the genome, effecting large scale natural mutation which ultimately leads to speciation. The theory seems to hold good when comparing North East India to South India, having humid Tropical and subtropical rainforest climate conducive for prolific production of epiphytic orchids. But if we compare orchid diversity among the States of North East India, we find Sikkim stands the second highest in orchid diversity next only to Arunachal Pradesh. According to the Tremor theory the State of Meghalaya should be having the maximum number of orchid species since the state is situated on the active tremor zone, but it is not so in reality.

The State Sikkim has only 7096 sq.km geographical area but has an unique geographical feature. The State is a rectangular piece of land which is 64 to 96 km long and 160 km broad. It is a totally land locked area and is squeezed in between two Himalayan kingdoms-the Kingdom of Nepal in the West and Bhutan in the East. It lies between lat. 27° 5° and 28° 9° N. and long. 87° 59° and 88° 56° E. A part of the southern boundary of Tibetan Plateau butts in right inside the whole northern boundary of Sikkim thus rendering the climate similar similar to that of cold desert. The horizontal Dongkya range and other ranges in its southern part form a formidable barrier arresting the monsoon rain from passing through thus making its leeward side dry and cold. Whereas the windward side on the southern part of the Dongkya range receives the maximum monsoon rain and thus give the area the wet alpine type of climate. The general trend of mountain ranges in Sikkim is from east to west-Mt Pandim (6691m), Mt Simvo (6811m), Mt Siniolchu (6887m), Mt Kabru (7338m) and Mt Narsing(5825m), but there are two main long south north directed ridges running parallel to each other 64 to 96 km apart. The Singalila range which is about 64 km long, almost starts from plains level, separates Sikkim from Nepal in the West and culminates near its northern extremity in world?s third highest mountain, the Mt Khanchendzonga (8598m). The Chlola range in the East in comparision is much higher in elevation and it separates Sikkim from Bhutan in the East. Besides that there is the deep Chumby valley separating Sikkim and Bhutan. In general the valleys are narrow at the top and broader at the base. But in Sikkim valleys are broad at the top. Broad valleys like Donkong, Gyamchona, Cholamu and Muguthang are stretches of plain areas with unique faunal and floral diversity similar to that of Tibetan plateau and worth seeing.

The Singalila Range on the west, the Chola on the east with Tibetan Plateau in the north virtually enclose Sikkim in a titanic horseshoe. There is an another central longitudinal spur which separates the great Teesta catchment in the East from the great Rangit catchment in the west, culminating at Moinam Peak (3234m). Besides these major mountain ranges the state is criss-crossed with variously and oddly directed mountainous terrains having their own mini-microshade catchment areas thus providing many different types of micro-climatic niches congenial for species speciation. The diverse aspect classification also supports the view. As we proceed from the gentle southern slopy mountainous region towards north, the mountain ridges become steeper and sharper. Besides that there is a wide range of altitudinal variation starting from 460 ? 8598 m. The major climatic zonations in Sikkim are Tropical, Sub-Tropical, Sub-Temperate, Temperate, Dry-Alpine and Wet-Alpine. Through deep valleys the hot and moist Tropical climate penetrates right into the heart of Sikkim State, providing hotter southern and cooler northern slopes. As such the famous Teesta valley Sal penetrates right upto the sothern slopes of Dickhu valley in the East Sikkim and Tikjek and Tharpu valleys in the West Sikkim.These unique geographical features having wide range of altitudinal zonations, rich humidity percentage in the air and the high range of prcipitations, makes the Sikkim state, pockets of many microclimatic niches, harbouring rich flora and faunal diversity differing from one valley to another.