QBARS - v9n2 Occurrence of Rhododendron Species in Bhutan Collected By R. E. Cooper In 1914 And 1915

Occurrence of Rhododendron Species in Bhutan Collected By R. E. Cooper In 1914 And 1915
By R. E. Cooper

The following paper by R. E. Cooper tells of his expedition to Bhutan in 1915. "The Rhododendron Handbook" does not carry the field numbers of this expedition. Though forty years have elapsed since the expedition, both the article, by Mr. Cooper and letter by the late Sir Isaac B. Balfour, Regius Professor of Botany, Edinburgh, to Mr. Cooper should still be of great interest. The Society is indebted to Susan Worthington, editor of the Quarterly Bulletin of the American Primrose Society for the loan of the original Balfour letter and the article by Mr. Cooper.- Editor

Sikkim is famous as the earliest home of Rhododendrons and eastward, across the Chumbi Valley which lies along Sikkim's eastern border, is a strip of similarly mountainous country called Bhutan.

Bhutan covers the southern slopes of the Himalayas for about 300 miles, and stretches a phalanx of valleys and spurs south for 50 miles from the clusters of snow peaks on the main chain, to the dooars of Bengal.

There are three regions - the western valleys running south from the big cluster of peaks dominated by Chumolhari; the central valleys whose heads ramify from a cluster of peaks due north of Punakha; and the eastern valleys which lie in the shelter of another set of huge snow peaks guarding the gap in the Himalayas through which the Kuru Chu flows from Tibet into India.

The lowest elevation at which any rhododendron was found, was in red sandy soil, beneath Pinus longifolia forest, at an elevation of 3000 feet; in the valley of one of the eastern streams, the Kuru Chu. The species being the common R. arboreum , and not likely to be hardy, was not collected but merely noted. The highest growing species was R. setosum , which ranged above 15,000 feet. A companion species, outstripped only in the last few hundred feet nearer the snows, was R. nivale . This may now be seen growing in the Edinburgh Botanical Garden (Rock Garden), the only plant in cultivation from the highest growing species.

Certain species were common throughout Bhutan in similar conditions. The lepidotum , setosum , and anthopogon , are found on the land above tree-level; the campanulatum and virgatum in the highest forests of spruce, birch, and juniper; the grande , triflorum , and edgeworthii in the lowest regions to have snow are the plants not hardy in this country except in favored spots, the arboreum and dalhousiae .

Between the lowest record from 3000 feet and the highest from the vicinity of 16,000 feet there grows a set of plants whose altitudinal habitats are indicated in the accompanying tables.

Of the three regions, the western valleys have a similar distribution of high elevation flora to their neighboring valleys of Sikkim. There is the scattered occurrence of arboreum and maddenii at the first definite change of the vegetation from the subtropical to the sub-temperate indicated by the appearance of oaks and magnolias. A little higher, big clumps and thickets of tall growing grande and hodgsonii appear in moist mossy forest. At the first appearance of moist conifers - Abies as opposed to dry conifers, pines excelsa - the tall and often moss-covered species of rhododendron thin out, and drifts of cinnabarinum , wallichii , wightii , and campanulatum appear in the undergrowth. The bush forms of campanulatum and wightii reach to the first, open hillsides which the tree forms have declined to clothe, but here they prefer the sheltered slopes.

Ranging above even the sheltered slopes and adorning the rounded turf clad crowns of the lower ridges that look out over the deep valleys, and are in turn overlooked by the high and aloof, rock and ice pinnacles of the mountain-tops, are the dwarf bushes of the species of nivale , setosum , lepidotum , and anthopogon . These form continuous stretches on the first low moors, but plants of these species are driven gradually with increasing elevations-to seek the hollows, and finally to live their life in the shelter provided by the gaps between big boulders of the moraine.

A definite feature of the covering of the highest treed and shrubby slopes in the valleys of Bhutan is the occurrence of any species at higher elevations on the south-east facing exposures than on any other.

On the timber line of the slopes of a rising valley that lifts its head to the primula-studded moors, grey screes, and glittering snowfields, spruce forest will be seen running thin. The trees, getting more and more scattered and dwarfed, will be seen, however, growing on eastern slopes several hundred feet higher than on the slopes across the valley, which may have only a few scattered junipers.

The development of Rhododendron species, which from being shrubs under trees become full light bearers through the fading away of the tree forms, follow similar lines.

R. campanulatum , cinnabarinum , and wightii develop a continuous covering to the hillsides, draping the slopes and old moraines into graceful sweeps and contours of verdure in a most pleasant fashion. Gaps in the mantle there are, usually due to water logging of the soil, where a sort of fairy ring may be decked out with primulas; or a terrace covered with the meandering waters of a small spring will provide a contrast with clumps of Allium and Primula , both sikkimensis , rising from the grey slabs of rock half immersed in the water.

In the region of anthopogons such wet terraces are populated with Prim. involucrata , while Primula sapphirina will stud with blue, any peat nodules that may be about.

The Central Valleys are the uppermost reaches of the valleys north of Punakha and Tongsa. The folk who live in these valleys are able, by withdrawing bridges from the few places there the precipitous cliffs allow descent to the water's edge, to keep out would-be visitors from the south.

The people themselves visit the capital to pay tribute during the winter when the streams are no longer swollen by the summer rains or melting snows and can be forded. A visit to the upper reaches meant a more elaborate outfit than I could carry, and was therefore abandoned.

Each valley was partly penetrated, however, one to 9000 feet, and the other to 5000 feet, but the area was not particularly profitable.

Tongsa's Valley was not visited, but the next valley to it was traversed throughout. This was Pumthang, and although it is included in the eastern valleys, this valley gave an excellent indication of what was across the ridge. The ridge flora was poor and uninteresting.

The eastern valleys yielded R. thyodocum from 12,000 feet, argipeplum from 10,000 feet, and kendrickii from 8000 feet, as the most interesting records of new and rare plants in a region where the disposition of the common species of the genus became similar in quantity and range to the western valleys.

So much for the general range and the extremes of the genus ranging up the valleys.

The valleys of Bhutan develop an arid tendency in places, usually about elevations of 7000 to 9000 feet, where 1 he hitherto steep-sided gorges from the south open out to wide valleys. The majority of the inhabitants live in these places, and the air being dry and the soil reddish and sandy, pines - P. excelsa - are the greater wear for the surrounding slopes up to certain limits. Connecting these habited areas of the valleys, a track traverses the country from east to west, crossing the dividing spurs at elevations about 10,000 feet. There seems to be something about the elevation of 9500 feet which induces rain, because in the most arid and pine-clad valleys, a moist flora develops at this elevation on the side hills. This means that the tops of the ridges separating valleys are crowned with moist forest, and in this rhododendrons, of course, are found.

Interesting records include brachystphon at 7000 feet, epapillatum at 6000 feet, keysii at 8000 feet, dalhousiae at 6000 feet, maddenii at 7000 feet, polandrum at 8000 feet, vacinioides at 9000 feet, and such epiphytic species as rhabdotum at 9000 feet, and cooperi at 9000 feet.

That the arid valleys have no effect on the range of species may be judged from the list showing the occurrence of species in the eastern, central, and western valleys.

A feature of the distribution of Rhododendron species in Bhutan was that as in Sikkim, the greatest quantities of these plants are found on the east and south-east aspects of the main Chola groups; so in Bhutan, much more rhododendron country was found south-east of the big Chumolhari group and the big group of snows which, according to the map, lies north of Punakha, and another big group by the gap through which the Kuru Chu flows.

Of species newly discovered but not necessarily in cultivation, there 1S haemonium , a dwarf shrub of the anthopogon type from the higher moors of 13,000 feet, with yellow flowers, found only in the western valleys, and two other high elevation plants - R. thyodocum , a 3-foot sprawling bush with purple flowers from 13,000 feet, and R. argipeplum , a 6-foot bush from 11,000 feet, with red flowers remarkable for a mass of white hairs in the open throat. These last two are only found in the eastern valleys.

R. papillatum is a 6-foot bush from the spruce forests of the western valleys of 11,000 feet, bearing pale-cream flowers frilled at the edges, with a blood-red blotch in the throat and scattered pink spots on the lip. R. kendrickii was only found in fruit at 9000 feet, but was effectively decorative through the crinkled edges of its long narrow leaves; looking more like a holly than a rhododendron.

R. rhabdotum was the showiest of the whole set both new and old. A 12-feet bush growing on dry rock faces, the flowers look very like a cross between a R. dalhousiae and an Ipomoea from the reflexed rim of the trumpet and the red lines running down the outside of the corolla tube to the peak of the petals. Found growing at 8000 feet, it would be hardy only in the south of England. Only one collection of this plant is on record, and that was in flower, so that it has yet to be introduced and established.

Taking Hooker's note on the journey to the Chola Pass in November 1849 of the order of ascension of Rhododendron species in the Sikkim hills, it is found to be very applicable to the range of the species on the Bhutan hills.

Has the direction or moisture content of the wind anything to do with higher ranging on certain definite slopes? Does the bedding of the rock belts which are tilted in one direction throughout the country affect the soil's composition and consistency? Who will venture an opinion when it is known that the winds travel up the valley and hillside for most of the day, and blow down the high slopes from the snows during the night? I can only testify from bitter experience that the air on these high slopes throughout the growing season for plants, from May to September, is a succession of blanketings of mist, sleet, and heavy rain, hastening before or with, bitterly cold winds.

The angle of dip of the rock beds is about 30 degrees to the north-west, the beds running north-east to southwest. This brings the broken ends of the strata on to the east facing or western side of the valleys, and those seem to be better for growing plants than the full rock face that underlies the thin layer of debris on the eastern slopes.

PLANTS IN CULTIVATION FROM COOPER'S SEED

The most interesting plants in cultivation at Edinburgh are Nos. 1805 obovatum from 13,000 feet, 2224 thyodocum of 14,000 feet, 2148 lanatum of 12,000 feet, 3482 setosum of 15,000 feet.

3483 nivale of 15,000 feet, 3485 anthopogon of 13,000 feet, 3492 wallichii aff. of 12,000 feet, all alpines and rock-garden plants.

R. nivale grows happily and well, producing quantities of flowers every year in the Edinburgh Botanic Garden (Rock Garden), where it is grown on top of a ridge exposed to all winds except those from the south-west (Edinburgh's most severe wind to plant growth if the prevailing slant of trees is any guide). This aspect will suit all the high elevation plants.

The other numbers included 2088 hodgsonii from 10,000 feet, 2315 and 3615 griffithianum of 6000 feet, 3505 thomsonii of 10,000 feet, 3506 cooperi of 9000 feet, 3507 smithii of 7000 feet, 3541 triflorum of 9000 feet, 3588 virgatum of 9000 feet, 3601 brachysiphon of 9000 feet, 4978 kendrickii of 9000 feet, and 2922 a cinnabarinum which has produced yellow flowers, all requiring protection in the winter, except in the warmer counties and exposures.

The numbers which have been referred to as affinities of campanulatum , cinnabarinum , and arboreum are from plants which seemed to show sufficiently distinct variation in the field to warrant collecting.