Chosenia II: An Amazing Tree of Northeast Asia
Many travelers to Northeast Siberia return with fond memories of the young chosenia groves they have seen. These riverside communities that harbor many showy flowering herbs stand out brightly against the otherwise monotonous background of the Siberian taiga. But even more impressive are groves of mature chosenias with their colossal trees, whose size is unusual not only for Yakutia, the coldest place on the continent of Eurasia, but even for lushly productive regions, such as Manchuria. The floodplain groves miraculously emerge on lifeless river pebbles in just some 10–12 years; the entire transformation from tiny chosenia seedlings on bare pebbles to majestic sixty-feet trees on fertile soil normally takes place in just 60–70 years! By then, the organic mass accumulation in chosenia stands reaches record amounts, which any other most productive kinds of the taiga forest may yield only in 150–200 years.
Chosenia arbutifolia (Pall.) A. Skv., one of the fastest-growing trees of Northeast Asia, is closely related to the willows. It has often been mistaken for a large willow even by experienced botanists. However, a close look at its catkins and flowers reveals clear differences from the willows. The nectaries or glands (structures that are found in any willow flower) are missing in the chosenia flowers; the stamens, pistils, and bracts look different from both the willow and poplar flower structures. The chosenia staminate flower has five stamens hiding under the bract and connate with it in the lower filaments; the pistillate flower has two styles, each with a two-cleft stigma. Like poplars, chosenia is wind pollinated, whereas all of the willows are insect pollinated. These peculiarities alone provided enough grounds for botanists to place chosenia in its own, monotypic (single-species) genus.
But the list of this tree's interesting traits is not yet exhausted. Chosenia also surprises us with very distinctive root system featuring the taproot (none of the willows possess this kind of a "carrot") along with unique anchoring structures. Its wood has a very unusual anatomic character: the so-called homogeneous rays. Chosenia's leaves are also quite special. Like the xeromorphic (water-saving) leaves of the primitive Turanga poplars and the primitive willows of the Section Longifoliae, they are somewhat fleshy and covered with bluish bloom, especially on young trees. This pruinose bloom also covers the tender young twigs, which gives chosenias their peculiar habit (Fig. 1). The twigs remain barkless for a few years and contribute to the photosynthesis along with the leaves. Later they develop brownish bark, which darkens with age. Old chosenias attain a captivating habit with their bark (Fig. 2) exfoliating much like that of shagbark hickory (Carya ovata), but unlike any of the willows (the bark of Salix triandra also exfoliates, but in a different pattern.)
Being strictly confined to a certain kind of habitat, the sandy-pebbly deposits on banks of mountain rivers, this tree, at the same time, has a huge geographic area ranging from the subtropical broadleaf forests of Honshu to the ascetic tundras in Siberia (the Anadyr River basin) and reaching along rivers beyond the Arctic Circle where no other tree of such a magnitude can grow. The vast area of chosenia comprises a major part of Siberian Russia east of Lake Baikal and the Lena River, the Russian Far East including Sakhalin Island and the Kamchatka Peninsula, northeastern China, northeastern North Korea; and the Islands Hokkaido and Honshu of the Japanese archipelago. (Fig. 3)
From sandals to telegraph poles
The peoples of Northeast Asia have long known, loved, and utilized chosenia for all kinds of industries from sandal-, clog-, and rope-making to fanza- and bridge-building. Chosenias have been used for making dugout boats with displacement capacity of up to one ton. This fact alone gives a sense of the impressive dimensions these trees can attain.
Among the northern reindeer breeders, chosenia is particularly valued as forage. In the wintertime, the reindeer dig diligently under the snow for fallen chosenia leaves, which contain unusually high amounts of ash and therefore serve as a calcium supplement for the animals in winter.
The most ambitious commercial venture in which chosenia played a role was a bold attempt in the 1860's by the Western Union Telegraph Company to build a telegraph line connecting North America with Europe via the Bering Strait and Siberia. However, when a competing company succeded in dragging a telegraph cable across the Atlantic, the Western Union gave up the entire project, and after several years of hard work the indefatigable leader of the Siberian expedition, George Kennan, had to abandon thousands of telegraph poles already prepared with great difficulty along the proposed telegraph line. Many of those poles were trunks of chosenia, which Kennan apparently considered to be a kind of large willow or poplar. At the Lower Anadyr he indeed could hardly find any material suitable for the poles other than chosenia trees. By the time the construction was canceled, this remarkable man had bravely surveyed the wildest and most remote regions of Northeast Siberia, notorious for their extremely harsh climate and very sparsely inhabited by nomadic tribes.
A new name for the old friend
No wonder that Kennan mistook chosenias for willows: Russian settlers of the Kamchatka Peninsula, where chosenia grows abundantly, have always called the tree vetla (a tree willow). Topol (poplar), its other Russian name, is used in Northeast Siberia (whereas real poplars are called 'aspens' there.) The Yakuts have called it tiryakh, which is also their name for a poplar (Populus suaveolens) that often grows in mixed groves with chosenia; for willows they have a different word, talakh. Chosenia's colloquial names also include: seiakhta and sikhta (respectively, in Nanayan and Udegeyan—languages of some of the small nations in the Far East); leo-mo and zhuantianliu—Chinese names; kesho-yanagi (the beautiful willow) and karafuto-kuroyanagi (Sakhalin black willow)—the names used in Japan. The confusion about this tree's identity lasted well beyond the time of the telegraph project. By the beginning of the 20th century chosenia had been observed by botanists multiple times. However, some mistakenly took it for a willow species familiar to them, others described it as yet another, new willow. No one realized that the proliferating names all referred to a single species.
The Japanese botanist Takenoshin Nakai once again "discovered" a strange new willow in Korea in 1918 (at the very beginning of his encounter with the tree, from 1911 to 1918, he also had taken it for another willow familiar to him). By 1920, he gradually came to the conclusion that he was dealing with something that wasn't quite a willow. He proudly introduced the tree to the scientific world as a new genus of the Salicaceae Family: Chosenia. The discovery of a new genus in such a well-known family produced a sensation in the botanical field! Educated Russians started to call the tree koreyanka, a Russian translation of the name Chosenia, which literally means 'an inhabitant of Korea' (however, this name didn't take and was gradually supplanted by the international 'chosenia'). Nakai did not identify his finding with many of the scientific names (Fig. 4) previously given to the tree. It took nearly forty years to completely clear up the lasting confusion: identify chosenia with its existing synonym names and choose the correct species epithet according to priority considerations.
The start: The first three hurdles
Let's now take a closer look at the tiny chosenia seedlings and the intricate path they must follow to survive and develop into majestic trees. At the very beginning of its life this remarkable plant depends completely upon the water flow and sediment accumulation that occurs in river floodplains. The Far East is famous for its unusual floods—severe, abrupt, and overwhelming, sometimes even catastrophic. They occur in summer rather than in spring, usually two or three times during the season. As the snow melts on the hills and mountains (sopka's), it adds to the pouring rains brought by the summer monsoon. These rains turn each river into a powerful stream that soon leaves its bed and fills the entire floodplain. Near the bottom of the riverbed, the wate is filled with great number of drifting pebbles that originate in the upper reaches. The amount of pebbles dragged by the water is enormous: the noise they produce sometimes becomes so loud that a person talking at the streamside can't hear his own voice. Each flood forms fresh pebble deposits (Fig. 5) along river banks and may cause the river to meander, that is, change its direction.
During late July–early August (often immediately following a summer flood) chosenia trees disseminate their abundant minute seeds, each as light as 0.25 mg, bearing a crown of white hair. The seeds cover the entire surface of the water, crowd the banks, and accumulate along the water edge. It is mostly on newly deposited pebbles, that they succeed to develop into seedlings. The seeds germinate right away, and multitudes of seedlings appear on bare moist pebbles at the edge of the flowing water. Due to the favorable conditions for germination along the water edge, entire stripes of chosenia seedlings of different generations are formed along banks of meandering rivers—and the older the plants, the more faraway from the water they are located. The young chosenia seedling is tiny: only one centimeter tall. The root, however, extends down as deep as 3–4 cm between the pebbles. (Fig. 6) Most of these little plants do not survive the next following flood. However, those that manage to hang on at least for a month become so firmly anchored amidst the pebbles that you cannot pull or even dig them out without breaking the root.
During the second year, the primary shoot dies back, and another shoot, larger than the first, starts growing. By the end of the second growing season, this new shoot becomes prostrate, with just the very tip ascending from the pebbles. Finally it also dies off giving way to three or four virgate (long and flexible) shoots during the third summer. These new shoots still hide from severe floods by lying flat on the pebbles, and the entire plant now attains a habit of a prostrate rosette. (Fig. 7, 8, 9)
Self-serving a nice layer cake
Juvenile chosenia leaves are somewhat different from those of the adult tree: they appear to be even more succulent, that is, fleshy, juicy, and covered with pruinose bloom, as if they were leaves of some desert species. There is nothing strange about this resemblance, since during the periods of drought between floods the bare pebbles around the young plants may become as hot as 50° C (120° F).
It is only during its third and fourth years that chosenia gradually abandons the prostrate habit and starts to grow as an upright shrub. (Fig. 10) By this time, the young chosenia already finds itself a few feet away from the flowing water edge. Of course, this happens due to the river meandering rather than any movement of the plant. Yet another important process contributes to "moving" the young chosenia plants away from the running water: their vigorous long shoots, particularly the lower ones, become damaged during floods, but do not fall off when dead, forming a thick brush-like network. This brush functions very much like whalebone catching efficiently alluvial material and forming large sediment deposits around the tree. The nourishing soil layer self-produced by chosenia for its own benefit may grow as much as 30 cm or more during a single flood. The older the plant, the higher is its position and the larger the distance from the edge of the open water, where it once started its life. If you dig into the soil in an old chosenia grove, you will find it to be layered like a cake with each layer representing a single flood, its lower portion consisting of coarse material and the upper parts containing fine particles.
The champion of the neighborhood
Every year the chosenia plants loose a large share of their branches. Young branches are rather brittle and break off easily (which is not unusual in the Family Salicaceae). During the summer floods, many branches are scratched by moving pebbles, but even more of them (up to half of all the branches) do not survive the harsh winters. Anything that protrudes from the snow dies back, if it is not consumed by moose or reindeer. However, this huge die-back doesn't hinder the growth. During its early years, this amazing tree performs rather like a semi-shrub producing one generation of branches after another. Every year the new growth becomes more and more vigorous, and the growth rate accelerates accordingly. (Fig. 11) By the age of five, a young chosenia may be adding up to a full meter to its height in a single season. Around this time, the sapling finally "realizes" that it is destined to develop into a majestic tree and produces a leader with a crown of powerful virgate shoots around it, all densely covered with thin and slender pruinose leaves. At this age the plant attains a habit intermediate between a tree and a shrub.
A few years later, when the crowns of the young chosenias merge, the trees start to thin out and develop into a grove typically consisting of some 30 to 100 trees. The grove still endures floods, but since the trees are now farther from the river, the water flows much more slowly and deposits fine particles rather than heavy pebbles. By the age of eight to ten, the trees become 7–8 m tall, their stems 10–15 cm in diameter. The leader starts to dominate; the only traces of virgate branches, which used to give the trees their shrub appearance, are dense brushes of dead wood at the bottoms of stems. (Fig. 12) These remnants continue to play their role as alluvium traps during floods.
A grove of young chosenias with its open canopy and fertile alluvial soil produces a quite showy plant community is brightened by abundant grasses, flowering legumes, and other herbs. However, herbaceous species found in the chosenia groves aren't specific for chosenia. These plants as well occur in willow, poplar or any other riverine woods. Some of them have a much wider distribution than chosenia and can be found even outside the river valleys. In northern Yakutia, for example, the legumes found in chosenia groves (species of Astragalus, Oxytropis, and Hedysarum) are also widely distributed in sparse larch forests and mountain tundras.
Chosenia's period of intensive growth lasts until the trees become about 30 years old. By then they normally attain heights of 25 to 30 m and trunk diameters of almost half a meter. There are records of chosenias as tall as 40 m and as thick as 1.5 m! The root system of an adult tree consists of a central carrot-like taproot that extends as far as 3 m and reaches the underground water table underneath the river bed. The entire surface of the central root bears scars left by moving pebbles. Plenty of thick and thin thread-like roots grow in all directions downward from the "carrot." At the depth of 30–40 cm, adult trees develop special anchoring structures: three to five horizontal appendages, each shaped like an anchor. This system stabililizes the tree in the most unstable environment. Adult chosenias successfully stand up against the wind and the majority of severe floods.
The crown of a young adult tree growing in open space is pyramidal: the lower branches grow at an angle of 60–70° from the trunk (Fig. 13), whereas the upper branches grow at a much smaller angle. Crowns of adult chosenia growing in dense groups are umbrella-shaped (Fig. 14). During the wintertime, chosenia trees drop the top tender portions of their branches. This may add to their ability to conserve water in extreme winter conditions of Siberia. The deadwood brush at the lower trunks persists for a long time, though it gradually looses its importance. Mature chosenia groves are found as far as 50 to 100 m away from the riverbed and occupy the central parts of the floodplain, which means they are situated as high as 1.5 m above the water level. Floods occur there only once or twice a year. It is dark and damp underneath the canopy of a mature chosenia grove. Only shade-loving grasses and herbs survive here.
The majestic trees aren't long-lived. They start to decline at the age of 70–80: first, the top dies back (Fig. 15, 16) and then pieces of the trunk start to break off from the top downward. Ugly outgrowths caused by bacterial attacks replace the brush at the bottom of the trunk. On average, if a thirty-year-old grove contains some 30 to 50 trees, then by the age of about one hundred there normally remain only some three or five of them. These patriarchs stand as far as 150–200 m away from the river and almost never experience floods. Poplar and larch trees tend to take over and succeed the chosenia groves.
Cultivated chosenia: A different story
If we now glance at the entire chosenia life cycle in nature, we will notice that this tree belongs to the type of plants that yield nice chunks of the environment to their more competitive neighbors, thus restricting themselves to unfavorable, difficult situations, where they, however, don't have to address competition. To be able to survive in the harsh conditions of the bare pebble deposits, chosenia has developed its very peculiar traits: a unique root system featuring a strong taproot along with anchoring structures; a prostrate habit at the very tender age followed by semi-shrub behavior for a few years; the succulent, water-saving foliage; the ability to collect and reserve nutritious material for itself by means of brush-like network of dead and broken lower branches.
Yet another distinctive character of chosenia is its plasticity, that is, the ability to suppress many of the adaptations in case they are not needed. You don't have to provide bare pebbles, Siberian winter temperatures, or harsh floods in order to grow a chosenia. With adequate moisture, light, and good drainage, it will do well in an average garden. When it does not have to meet the challenges of the life in the wild, it demonstrates its unique abilities in a very subtle manner. In cultivation it would start its life as a "normal" tree seedling. Though chosenia seedlings easily become distorted, they never develop a truly prostrate habit and tend to produce a few weak roots rather than one tap root. Their juvenile leaves don't look much different from the leaves of adult trees. The tendency to cast branches is rather pronounced even in cultivation; new generations of more and more vigorous branches are produced yearly, though this ability never develops to such extremes that the plant would perform as a semi-shrub. The shrub appearance isn't that much characteristic of cultivated young chosenias, either: they tend to develop leaders and start to grow as trees earlier than in the wild. Indeed, the most challenging part of growing a chosenia in the garden is the propagation itself. Unlike most willows, chosenias are difficult to be grown from cuttings. At the same time, the seeds loose viability very quickly, thus leaving little hope for the propagation success when the seed source is remote.
This narrative is based on the following literature:
Golysheva, M. D. 1973. [On the structure and formation of the leaf in Chosenia arbutifolia (Pall.) A. Skvorts.] — Bot. zhurn. 58 (12): 1764–1774.
Kennan, G. 1910. Tent life in Siberia. A new account of an old undertaking. Adventures among the Koraks and other tribes in Kamchatka and northern Asia. Gutenberg eBook Project. Release date: 12 May 2004.
Kolesnikov, B. P. 1937. [Chosenia and its communities in the Far East.] — USSR Acad. Sci. Far East Branch Proc., ser. bot. 2: 704–800.
Makryi, T. V. and L. V. Bardunov 1977. [A finding of Chosenia arbutifolia (Pall.) A. Skv. (Salicaceae) west of the Baikalsky Mountain Range (Cis-Baikal Region.)]— Bot. zhurn. 62 (11) 1669–1671.
Mazurenko, M. T. and T. A. Moskalyuk 1989. Ontogeny of Chosenia arbutifolia (Salicaceae) in the Magadan Region. — Bot. zhurn. 74 (5): 601–613.
Moskalyuk T. A. and M. T. Mazurenko1992. [An amazing northerner—chosenia.]— Priroda 12: 52–59.
Norin, B. N. 1958. [Some characters of chosenia communities (Chosenia macrolepis Ass.) at the extreme northwest of their area.]— Bot. zhurn. 43 (6): 847–850.
Sheludyakova, V. A. 1943. [Chosenia in the Republic of Yakutia.]— Bot. zhurn. 28 (1): 30–33.
Skvortsov, A. K. 1957. Commentationes de morphologia et systematica salicarum. IV. [On the correct species epithet for Chosenia.] — Bot. mat. Gerb. Bot. in-ta AN SSSR 18: 42–47.
Trofimov, T. T. 1964. [Some interesting Far East plants in the Moscow University Botanic Garden.]— Bot. zhurn. 49 (11): 1563.
Yegorov, A. D. and V. B. Kuvayev 1958. [Chosenia and broad-leaved fireweed—promising forage plants for the reindeer.]— USSR Acad. Sci. Yakut Branch Reports 1: 92–95.
6 Feb 2005