saxaul (Haloxylon ammodendron), black saxaul (Haloxylon aphyllum),
white saxaul (Haloxylon persicum)
by Jay Sharp
The homely-looking saxaul, roughly the size of the typical tamarisk, or salt cedar, ranks as one of the most important and useful native plants in the arid region from the Caspian Sea eastward across the Gobi Desert.
Characteristics of the Saxaul Tree
The saxaul comprises three closely related species, including the saxaul (Haloxylon ammodendron), the black saxaul (Haloxylon aphyllum) and the white saxaul (Haloxylon persicum). All the species have developed considerable tolerance for aridity, wind, salinity and limited nitrogen.
The mature saxaul usually stands about six to perhaps 12 feet in height. Both its trunk and branches are heavy and coarse, crooked and knotty, with a thick, sponge-like, water-saturated bark. The mature plant has a succulent root system that reaches out extensively for water, both laterally and deeply, with more success in sandy than in heavily textured soils. The mature plant produces minuscule yellow flowers. It has leaves so small that they may not be readily apparent-- an adaptation that helps minimize the loss of moisture through evaporation in the desert environment. According to authorities, A. Shahbazi, K. Nosrati, and G. R. Zehtabian, the saxaul uses its succulent stems for photosynthesis. The mature saxaul has a dull gray trunk and branches. The young saxaul has vivid green and pendulous, or hanging, branches.
Distribution and Habitat
The distribution of the saxaul (Haloxylon ammodendron) extends from Iran and Central Asia eastward across the Gobi Desert, and that of the black saxaul (Haloxylon aphyllum) and the white saxaul (Haloxylon persicum), across Iran and Central Asia. The saxaul grows -- sometimes as the only shrub or tree -- in harsh habitats such as moving or fixed sands, saline depressions, dry canyons, clay and rock submontane planes, rocky hill and mountain slopes and tertiary badlands. The Haloxylon ammodendron grows in all five ecoregions of the Gobi Desert. In southern Mongolia alone, saxaul forests have covered millions of acres of land.
Typically, the saxaul flowers in the late summer into the fall, and it produces mature seeds by the end of the winter season. Its seeds scatter through the summer, beginning a rapid germination, if conditions are right, in the early fall. Unlike many desert plants, the seeds have relatively brief viability, less than a year, in unfavorable conditions.
In studies by the Chinese Academy of Sciences and other institutions, saxaul plants in "sandy soil developed much deeper root systems, larger root surface areas and higher root [to] leaf surface area ratio than in heavy textured soil..." This "facilitated plants acquiring more water and surviving the prolonged drought period." As Chinese researchers Wei Jiang, Zhang XiMing, Shan LiShan, Yan HaiLong and Liang ShaoMing said, the root structure grows faster than the trunk, branches and foliage in the early stages. The plant's extensive root system also provides anchoring during seasons of intense winds.
Under favorable conditions -- for instance, along a desert drainage -- a "forest" of saxaul shrubs or small trees may develop, and an individual plant may live for several decades. Under more harsh conditions, widely scattered stands of saxaul develop as the dominant plants in a region.
The saxaul serves a number of purposes across its range. For instance:
- Its spongy, saturated bark can be pressed to extract drinkable water--a critically important commodity for nomadic peoples of the Central Asian deserts. Its wood serves as campfire fuel for warmth and cooking. It provides fodder for livestock.
- The saxaul supplies cover and forage for wildlife, for instance, the wild Bactrian camel, the ibex and various bird species. The saxaul sparrow, as one prominent example, feeds heavily on saxaul seeds, especially during the breeding season.
- The plant's wood yields a green dye that Turkmenistan's traditional weavers use for coloring wool yarn that they incorporate into their exquisite carpets.
- Planted extensively in the arid regions of China, the plant serves as shelter belts to impede wind erosion and stabilize sand dunes, helping counter the process of desertification.
- The saxaul's roots host the parasitic plant cistanche, which traditional Asian herbalists use to produce a salty-tasting medicinal component that they use in treating ailments as diverse as infertility, age-related lethargy, blurred vision, memory loss, baldness, balance disorders and heart palpitations, according to Subhuti Dharmananda, Ph.D., Director of the Institute for Traditional Medicine, Portland, Oregon. Cistanche is sometimes called the "ginseng of the desert."
Over the past several decades, saxaul forests have shrunk dramatically in many areas across its range both in terms of coverage and growth rate. It is apparently suffering as a result of climate change, which may be increasing the desert's aridity beyond even the saxaul's tolerance. Undoubtedly, the saxaul has declined because growing human populations are turning more and more to the plant's wood for fuel in lieu of increasingly expensive coal and petroleum-based products.
The saxaul has become a dwindling resource for humans, livestock and wildlife. Its disappearance opens the way for the erosion of fragile desert soils, decreased natural control of water supplies, and an acceleration of desertification. The plant has even been listed as being at risk of extinction by at least one source.
The decline of saxaul forests in the arid regions of Mongolia may account for the increasingly harmful sandstorms in recent years, according to researchers B. Suvdansetseg, H. Fukui and R. Tsolmon. Within their study area, the forests of saxaul -- the most important native plant in the region -- had contracted by some 50 percent over 25 years.
- The saxaul is the only plant that can grow in all the ecoregions of the Gobi Desert.
- As a host plant, the saxaul's roots provides chlorophyll, nutrients and water to the parasite cistanche, which can grow to several feet in height.
- Paralleling the saxaul, the cistanche may become endangered, both because of the decline of its host plant and because of its popularity in Asian pharmaceuticals.
- During the 19th century, the saxaul was used, experimentally and briefly, as a fuel source for Russian steamships stationed in the land-locked Aral Sea, according to historians John Michell, Chokan Chingisovich Valikhanov and Mikhail Ivnovich Venyukov. However, the hard, knotty, crooked wood proved difficult to cut to size and to store in ship holds. The experiment was soon abandoned.
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