Types of orchid population in South Inida

The vegetation on the Western Ghats in general is constituted by what is typically designated as tropical rain forests . But depending upon the amount of rainfall ,there may be differences in the type and amount of vegetative growth in different parts of the mountain range. As was explained earlier in this chapter , the western slopes of western Ghats receive for heavier precipitation than any other part, which are naturally considered as rain-shadow areas, where the orchid vegetation is mostly composed of succulent species like Luisia ,Diplocentrum, Oberonia etc. , and hardly forms like Vanda spathulata ,V. tessellate and V. testacea.

Sea level -300 m

The Western coastal plains,due to its heavy annual rainfall and the juxtaposition to the sea along its entire length, retains a high amount of moisture in the atmosphere . but temperature is too high for most species of orchids. The 5-6 species which survive this temperature ,however, thrive and proliferate to such an extent that practically every tree is covered by one or more of these species .Acampe praemorsa, Dendrobium macrostachyum , Luisia zeylanica, Pholidota pallida, Cymbidium aloifolium, Bulbophyllum neilgherrense are the species which are found in the plains. There is only one terrestrial orchid which occurs commonly at sea leavel-Eulophia epidendraea.

As we get nearer to the mountain ranges the density of orchid population increases . Species like Rhynchostylis retusa ,some Oberonias , Vanda testacea appear on the trees. Malaxis versicolor ,Geodorum densiflorum are found among terrestrial forms .

300-600 m

As we go up the mountain ranges ,the forest thickens and temperature falls at the rate of 1 degree F for every 95m. Oberonia brunoniana ,Dendrobium ovatum, Polystachya flavescens, and Aerides ringens appear and intermingle with the previously mentioned species , which gradually disappear.

600-300 m

This is the region of the typical rain forest . Huge trees, often more than 30 m. in height, form a thick canopy of leaves, through which little light penetrates. Undergrowth is reduced to a minimum. Calanthe masuca , Acanthephippium bicolor, Eulophia macrostachya , etc. , grow on the forest floor, in the dense shade while species of Malaxis and Liparis occupy regions nearer to grasslands ,where light penetration is high. Epiphytic species are rare due to the scanty light penetration. Those species which require perpetual moist conditions such as Dendrobium heyneanum ,various Eria species with discoid pseudo-bulbs , Cymbidium pendulum, Gastrochilus pulchellus etc., are the main occupants of tree trunks . A few species which require plenty of sunlight such as Eria pauciflora, Malleola gracilis etc., also are found at this altitude, but always occupying the topmost branches of the trees, so that no amount of sunlight is missed .

1300-1700 m

The rain forests thin out . The fall sparsely branched trees of the tropical rain forests give way to small , stunted trees with spreading branches . Wide expanses of grassaland appear in between clusters of trees. Gallery forests, i. e., encroachments of forestlands into grassland along temporary stream beds or park savannahs , i. e.,grasslands with scattered clusters of trees here and there are a min feature of the mountain ranges of this altitude. Actual rain fall in this area may be lower than in the rain forests , but there is always a nightly mist which more than compensates for the diminished rainfall . Plenty of sunshine is available and free air circulation is possible . This is the ideal orchid country and here we find the majority of orchid species which are epiphytic , thriving luxuriously on the stunted trees. Dendrobium heterocarpum ,Dendrobium nutans ,D. microbulbon, D. nanum, the various Cirrhopetalums , etc. , reach their maximum growth here. The various terrestrial tuberous forms like Habenaria , Peristylus , Pecteilis etc., Eulophia nuda,E. cullenii etc. also thrive in the grasslands , in full sunshine.

1700-2300 m

Mostly savannahs . Here it is too cold and dry for epiphytic species. Except for a few species of Coelogynes, Cirrhopetalums and Aerides maculosum ,not much of epiphytic species is seen. Habenaria and its allies continue to occupy the meadows though at a diminished frequency.

2300 m and above

No epiphytes. Even the terrestrials vanish .