Sikkim State Council of Science and Technology

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HABITAT

  In general sense, the rhododendrons are essentially terrestrials in nature. Under suitable environment the epiphytes are always found growing on soil albeit the ground is a raised earth, rock or sloping. The epiphytes species of the group are R. camelliiflorum, R.dalhousiae, edgeworthii, griffithianum (to some extent), leptocarpum, lindleyi, and vaccinioides. For these the major phorophytes are species of Castanopsis, Quercus, R.arboreum, etc. Generally, trees with a longer lifespan and rough bark were found to be preferred as phorophytes. But this is not a general rule as because it is seen that the epiphytes, conditions permitting, makes use of almost any available tree species that is found in the locality as epiphytes.
 Some of the species which grow also no rocks are R. fulgens, lepidotum, nivale, pendulum, setosum, camelliiflorum, and to some extent anthopogan and baileyi. At favourable location, it seems, almost all species take to rocks as refuge.
 Species which require shades to a varying degree are R. lanatum (under Abies sp) fulgens, decipiens, wallichi, wightii, and campanulatum (all under mixed community of dominant Abies sp). All other species may be classified as ‘outdoors’ as because they grow quite well in the open.
 Most of the bush /bushlets are found on open sloping terrain. The slopes somewhat well drained and thus less moist condition where few species make their home, e.g. R.virgatum, R. pendulum, etc. The epiphyte rhododendrons which are found sometimes growing on soil are generally restricted to the sloping terrain where water-logging is less experienced (as is the situation on a tree environment). The shrub favour level grounds, the river –terrace being their favourite retreats.
 At Barshay, the R.falconeri though grows in marshy locality, never step into the marsh but choose the adjacent grounds which are less moist. Similarly, the R.ciliatum at Yakchay they grow on marshy places and at the adjacent non – marshy sites R. niveum covers the remaining ground. As all marshy places are usually on even grounds the species that grow here was seldom found growing on the slopes.
 The species which are trees or reaching a tree like dimension are sometimes found as canopy members inside a forest stand, some still are found as dominating species occupying the upper story as is the case found at places like Tendong peak. (R.grande) and Hillay – Barshay (R. falconeri) covers the crown of a small knoll and outgrows all associated trees in height.
  Rhododendrons here usually grows under a moist environment with plenty of soil moisture, humidity and at the location above 2800m spend about 3 months under snow. Winter with severe drop in temperature at localities above 2800m produces permafrost of situation in the soil. A physiological drought condition is thus always experienced by these plants at such localities. To fend off such tundra –like condition (for the snow and frozen groundwater are not available to plants at such times) various modifications come up in the form of scales, hairs on the leaves and its curling. Growth is therefore always thwarted at such localities.
 The species which experience and grow over regular snow-line and avalanche are R.niveum and R.thomsonii. The response to sheer stress of snowline and now made the R.thomsonii at Phuni to be growing in an inclined manner.
 The soil in most of the rhododendron growing sports showed high nitrogen content( 490 kg/ha). < 4% organic matter, Phosphorus at 145/kg/ha (P2O5) and low Potassium (48 kg/ha). Mean for pH was 5.6.
  Soil, as is expected, was towards acid. Soil pH for individual cases is presented in its respective entries.
  The habitat of R.niveum and R.thomsonii population (at Yakchay through Phuni) are regularly subjected to avalanches. This natural force has an ancient history or is of a origin is difficult to assess but considering the devastation of R.niveum at Yakchay during the 1980 snow-line and sheer bending away of R.thomsonii. towards the river –side points to the fact that the casualties has a recent origin.
  In conclusion, the habitat of both the epiphyte as well as terrestrial rhododendrons require consideration towards its preservation.

Horizontal Distribution: Lachung valley
  Under observation the species were found to be quite ‘site specific’, or conversely, small locality or rather niche quality played important part in the species being found or not. The many clearly demarcated niches of 9 rhododendron species is rather starkly obvious at this area. Small virtual ‘islands’ of these niches sometimes overlap. Highly delicate ecosystem balancing mechanism must be operating in the area to support such a diversity in form habitat and the harmony. The watershed of Lachung chhu still has the scope to be studied in its totality unlike the Singalila ridge which has lost a large part of its natural biota and virgin terrain.
  Small patches usually were found to be harboring a group of particular species, fro example, in the Yakchay area R.niveum is localized. Here, not a single species of R.thomsonii is found whereas about 1km away (aerial distance) at Phuni these grow in impenetrable thickest. And here not a trace of R.niveum is found. The altitude differences is 100m only. A little more up between 3000-3700m above mean sea level R. campanulatum grows luxuriantly up to Yumthang. Between this patch is found R.baileyi for a short stretch. Others are R.decipiens at Shingba (3200m), R.cinnabarium (3500m), and small patches of R.wightii, R.setosum and R.grande. Interspersed between these are found the less gregarious ones, e.g. R. lanatum, R. pendulum, R. fulgens. A little up from Yumthang one can observe R. aeruginosum (scattered), R. campylocarpum (in swarms), etc. Yakchay proper is also the location of R.ciliatum.
  At Lachung proper the slopes are usually found covered by R.virgatum facing south east. Same is the case of R. lepidotum.
 

Horizontal distribution: Yuksam-Thangsing area
  So far, the Yuksam-Thangsing area (map 3) remains one of the best preserve for Sikkim Himalayan rhododendrons. It is in this area that the first sighting of R. leptocarpum was made. Different terrain, absence of pliable road and presence of intact natural forest cover has contributed much in the stability of the environment and preservation of rhododendrons in the region. Most remarkable is the comparatively large size of epiphytic rhododendron population. Once this particular trail was an important pilgrimage trail and under the royal patronage (Yuksam being the former capital of sovereign Sikkim) and disturbance to the land and biota was not allowed. This regulation was put to effect as because the trail led to sacred places, lakes and monasteries. The route from yuksam to Thansing is c 30km and covers 3000m in elevation. This is also the more frequented route fro reaching the base camping site for Kanchendzonga National Park.