The Ecology of the Rhododendrons on
Milke Danda Ridge, Eastern Nepal
The Milke Danda is a ridgeline rising from the hills of Eastern Nepal into the jagged mountains
to the north bordering Tibet. The ridge stretches over twenty miles and, by Himalayan standards,
rises gradually over most of its length although the side slopes are generally steep dropping
2000-3000 meters (6,600-9,900 ft) to the river valleys below. The southern half of the ridge has
a temperate climate while the northern part reaches up to 3800 meters (12,500 ft) and has a
cooler, sub-alpine climate with intermittent snowfall. At its northern extremity, the ridgeline
climbs steeply into the "small" Jaljale Himals reaching up to 5300 meters (17,500 ft).
By early afternoon, even on clear autumn days, the ridge top is usually covered by clouds and quite often raining or, at least, misting. The ridge is a cool and damp place because hot, moist air rises 3000 meters (9,900 ft) from the adjacent river valleys, cools and condenses along the ridge top. This daily precipitation combined with the constant cool temperature at this altitude has led to nutrient poor, leached out soil. It is here that rhododendrons outperform other trees and have created pure rhododendron forests. Unlike most other ridges in Eastern Nepal, the Milke Danda gradually gains altitude through the temperate and sub-alpine elevations and so has a relatively large continuous and accessible area where rhododendrons are the dominant tree species. Rhododendrons fill a wide variety of ecological niches - from the dominant tree species up to 30 meters (100 ft) tall, to small epiphytes and alpine shrubs. There are around twenty species found on the ridgeline (I have identified sixteen species and have discovered a few more but not identified them). Although perhaps not quite as species rich as areas to the east in Sikkim, Bhutan and China, the ridgeline is interesting because of the mix of Western and Eastern Himalayan species and subspecies in the overlap of their ranges. With such a large area, there is also a wealth of intra-species genetic diversity. It is an excellent area for observing rhododendrons because one can see most of the ridgeline over a few moderate (a relative term in the Himalayas!) days of walking.
As a Peace Corps volunteer in Nepal, my main work was with communities on the slopes of the ridge. However, over the course of three years I have spent many wet weeks on the ridgeline learning the ecology of the rhododendrons. As no significant research had been conducted, I sampled over eighty small plots along the sub-alpine portion of the ridge to provide preliminary baseline information on the rhododendrons and to learn more about how humans are affecting them. Although the subalpine area is not suitable for farming, local communities graze sheep, cows and yaks in the rhododendron forests and cut rhododendrons for firewood.
Tree line rhododendrons, Milke Danda ridge, Nepal.
Photo by Erik Steffens
The sub-alpine region has the largest diversity of species (eleven identified) and is personally the most interesting. However, rhododendron species and composition changes with altitude so it is worthwhile to describe the lower elevation rhododendrons and work up into the alpine.
Starting above 2000 meters (6,600 ft) along the lower southern ridgeline and slopes in places of poorer growing conditions, Rhododendron arboreum (the national flower of Nepal) grows in pure stands up to 30 meters (100 ft) tall. Subspecies present include cinnamomeum and album. In better soil, oaks are the dominant tree species and provide habitat for epiphytic rhododendrons such as the large and fragrant R. lindleyi and R. dalhousiae. Other epiphytic species are assumed to be present although I have neither seen nor actively searched for them. Rhododendron triflorum also grows as an understory shrub. Rhododendrons at these altitudes are usually in full bloom in late April into early May and turn whole hillsides red and pink. They are especially impressive just after peak bloom when a gust of wind will send hundreds of corollas fluttering softly to the ground.
Photo by Erik Steffens
A little higher in elevation, Rhododendron grande, R. falconeri and R. barbatum grow on wetter, eastern and northern facing slopes. The deciduous Magnolia campbellii is also present and blooms in early May with huge fragrant white flowers on bare branches.
As one climbs to the north along the ridgeline above 3300 meters (10,900 ft), pure stands of mixed rhododendron forest from 3 to 9 meters (10–30 ft) high become predominant. In mid May, when these rhododendrons are in full bloom, hillsides are covered in white, lilac, crimson, magenta red and yellow. Yaks graze in small grassy clearings surrounded by up to seven species of Rhododendron. I imagine many of the readers have spent lifetimes to produce a similar effect in their own gardens!
Rhododendron campanulatum is a profuse bloomer generally found along the edge of the grassy areas and cliffs. It has loose corollas of white to deep grape, varying degrees of spots on the upper corolla and soft, thick indumentum. Subspecies campanulatum is prominent from 3300 to 3700 meters (10,900 to 12,200 ft). Above this, specimens start to exhibit predominantly the characteristics of subspecies aeruginosum with its strongly reflexing leaves and thick orange indumentum. The transition between subspecies at this elevation is less than distinct with many specimens showing traits of both.
Photo by Erik Steffens
Although Rhododendron thomsonii is represented by one subspecies - thomsonii, there are five distinct variations present on the ridge differing slightly in size, shape and color of the characteristic red wine/magenta corolla and calyx. Two unusual specimens with a pinkish white corolla were found at the higher end of this species distribution at 3700 meters (12,200 ft). This species is dominant on eastern and southern exposed slopes and generally does not grow over 4 meters (13 ft). However, it can have a large girth up to 90 cm (36 in) diameter at ground level. The other dominant large rhododendron at this altitude is R. hodgsonii. With its naked pealing bark and soccer ball sized pink and crimson racemes, it is mystical in the mist. It is the most predominant climax tree growing up to 9 meters (30 ft) and its seedlings regenerate well in the understory.
Most rhododendrons at this altitude grow two to four large trunks that separate within three feet of the ground. Rhododendron cinnabarinum is more shrub-like and usually has a multitude of branches reaching no higher than 3 meters (10 ft). As would be expected, R. cinnabarinum seems to be an early successional species colonizing quickly in forest openings and disturbed areas. It is unique among the rhododendrons, as it is edible to livestock and has the ability to regenerate through root suckers. Color variations include one and two tones of scarlet, yellow and salmon. The scaly alpine shrubs R. anthopogon ssp. hypenanthum (a Western Himalayan subspecies) and R. lepidotum also appear on rocky outcrops.
A particularly beautiful forest type is seen on the eastern slopes as rhododendrons mix with the Eastern Himalayan silver fir (Abies densa). It forms an open canopy 20 meters (65 ft) above a beautiful understory of slender bamboo, the red flowers of Rhododendron barbatum and the yellow of R. campylocarpum. Red pandas are still thought to inhabit these forests.
The flowering of the rhododendrons provides a well-timed pulse of energy into the sub-alpine ecosystem. The nectar and pollen of the rhododendrons are a significant food source for insect and bird populations. In almost every flower, there is at least one large insect feeding on the nectar. A large variety of insects is seen although ants, moths and crane flies are most common. Gleaning birds, including four kinds of tits (like chickadees), yuhinas and warblers, fly from flower to flower and pop their heads in upside-down (perhaps an unsuspecting pollinator?) hunting for insects. Many times the insect cannot be reached so the bird tears a large hole in the base of the corolla. I've seen tits completely demolishing flowers to catch their bug. Many flowers end up with such bird inflicted war wounds and also a small hole at the base of the corolla made by the long slender bill of the fire tailed sunbird. The male is only 12 cm (5 in) long but has a bright red tail longer in length than his iridescent yellow and blue body. With its bright colors and peculiar manner of flying, it resembles a mystical nymph more than an avian species. Sunbirds diet on nectar like the hummingbirds in the Americas - only instead of hovering, the firebird stands on the flowers pedicel and punctures the upper base of the corolla. I am uncertain if the sunbirds actually play a significant role in pollination of the rhododendrons. Certainly, much pollen is transferred onto their feathers as they roll around in the racemes. However, the behavior of the gleaning birds would seem to provide a much more direct method of transfer of pollen. It would be interesting to study their different behavior and the accumulation of pollen on these potential pollinators.
To the north, the ridgeline steeply climbs over 1000 meters (3,300 ft) into the Jaljale Himals. In the few areas where the slope is conducive to vegetation, tree line is around 3800 meters (12,500 ft). Rhododendron composition changes little up to tree line from the common species found lower in the sub-alpine zone, the only changes being the cessation of Rhododendron thomsonii above 3700 meters (12,200 ft), and R. campanulatum ssp. aeruginosum replacing ssp. campanulatum.
On the south facing slopes above tree line, winter snow melts quickly creating an extreme environment where plants are exposed to freezing and desiccation. Here, rhododendrons are replaced by hardy sedges (Kobresia) and wild flowers such as primulas and gentians. In places where snow is less quick to melt and insulates plants, fragrant rhododendron shrubs are dominant. Swaths of Rhododendron anthopogon, R. setosum and R. lepidotum carpet the ground up to 50 centimeters (20 in) tall. The hardy R. nivale grows even higher up to 5300 meters (17,500 ft). In extremely sheltered spots such as on the north side of large boulders, R. campanulatum ssp. aeruginosum grows as high as 4300 meters (14,200 ft). At this elevation, its indumentum is extremely thick. These alpine species bloom in mid June to July. The leaves and stems of R. anthopogon and the other alpine species are collected in bulk and used in making incense.
Nepalis have separate names and can distinguish between the alpine species as each has different qualities and uses for incense and worship. "Sunpate" or R. anthopogon is of superior quality for making incense.
A day's climb into the rugged Himals is a lake sacred to both Hindus and Buddhists. It has been estimated (perhaps exaggerated) that 5000-8000 pilgrims journey to the lake every year for the full moon in August when the alpine meadows are filled with wildflowers. August is peak monsoon season and it can literally rain for weeks with hardly a break. The pilgrims usually travel with a pot, wool blanket, a large knife called a kukhri and about a week's worth of rice. They cook over fires made of rhododendron wood and usually cut and carry a bundle for their fires up above tree line. The choice firewood in these elevations is rhododendron. The small branches, even when green, burn speedily and the larger pieces also burn well because of their denseness. The most critical threat to the subalpine rhododendrons on the ridge is cutting for firewood by herders, pilgrims and trekking groups. Herders use the greatest amount of firewood as they live for months at a time on the ridge. They not only use wood for cooking and keeping warm but also use large quantities in the process of making butter and a kind of cheese. In order to dry and season the wood, patches of forest about ten meters wide are felled in August for use in the next grazing season starting in May. Only up to 20 centimeter diameter branches are cut as the herders carry only their large knives. In some areas this has left large stumps 4 feet high and a considerable amount of wood to rot. Few trekking groups come to the sub-alpine ridgeline. However, they tend to use large amounts of wood for entertainment of the trekkers and to keep the usually ill-clothed porters warm.
Photo by Erik Steffens
It seems that limited, selective cutting has increased diversity of rhododendron species in some areas because the larger specimens of Rhododendron hodgsonii and R. thomsonii are cut thereby leaving openings for the smaller, colonizing species such as R. cinnabarinum and R. campanulatum. The problem is the slow growth rate of rhododendrons at this altitude. Rhododendron hodgsonii at 3600 meters (11,900 ft) generally takes about 100 years to reach a diameter of 20 cm. Regeneration does occur in most conditions (in one five meter plot in an older cut over stand, there were over 500 seedlings). However, cutting seems to be far outpacing the rate of regeneration. Areas around herders stone shelters are the most degraded.
Another potential factor affecting the rhododendrons is the addition of yaks to the grazing cycle. Traditionally, sheep and cattle were grazed on the ridgeline for about three months every year. Twenty years ago, yaks and yak/cow cross breeds started grazing in the fall and spring as well. The increased pressure has caused sheet erosion and grassland deterioration. However, grazing itself might be in some ways beneficial for the rhododendrons. All species of rhododendrons found on the ridge (except Rhododendron cinnabarinum) are poisonous or unpalatable to livestock. Other tree species seedlings are eaten by livestock perhaps giving rhododendrons a regenerative advantage. Trampling may damage seedlings. However, the soil disturbance caused by overgrazing might create conditions ideal for germination for some species of rhododendrons.
The limited research I have conducted on the ridgeline indicates that areas bordering grazing lands contain a higher diversity of rhododendron species as compared to areas 30 meters (100 ft) distant. The higher diversity might be linked to the impact of grazing, but it may also be because rhododendron diversity is naturally higher in areas that are also good grazing areas and the "edge effect." It is hard to judge what effect grazing is having as there is no baseline information to compare to, and considering the slow growth of plants at such a high elevation, the results collected probably are a better indicator of old practices decades ago than recent overgrazing and cutting. I plan to interview and document the local communities' memory of specific areas and their remembrances as to how the land and the rhododendrons have changed over the years. It would be interesting and useful to determine how the rhododendrons are changing over time and the impacts of recent human actions. More importantly, there is a need to determine the best course of action to allow the users of the ridge to conserve the rhododendrons and still benefit from the natural resources on the ridge.
Recently, a number of government and INGO organizations have started considering making the ridgeline a rhododendron conservation area. Some organizational infrastructure has been set up and a few small projects implemented in the name of conserving the rhododendrons. However, an inadequate amount of research has been conducted to firstly understand and accurately assess the rhododendrons' current status and major threats. The concerns, problems and practices of the local communities must also be understood and incorporated into a management plan that keeps decision making local. They have an intricate system of traditional tenureship and are naturally (and wisely) fearful of government intervention. My hope is that the local communities will remain in control of the area and that outside organizations will support them as they conserve and utilize the Milke Danda ridge. I see the potential for the ridgeline to be developed as the "Rhododendron Trek" of Nepal where flower lovers can enjoy the spring bloom and morning mountain views. Mt Everest, Lhotse, Makalu and Kanchenjunga - four out of five of the world's highest peaks - are less than thirty miles away and are spectacular in the usually clear mornings. There is also great potential for research and education. My hope is that the rhododendrons will continue to thrive and diversify using the considerable rhododendron genetic "pool" there is now on the Milke Danda and, most importantly, that the local communities will benefit the most from conserving the rhododendrons.
Erik Steffens was a Peace Corps volunteer in Eastern Nepal. He is currently attending the University of Wisconsin in the Conservation Biology and Sustainable Development masters program.