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Biomes and Regions of Northern Eurasia

Arid Environments

<<< Biota and Soils | Biomes & Regions Index | The Mountains of Northern Russi: Introduction >>>

Human Impact on Ecosystems

As in many other arid regions of the world (i.e., the Middle East, North Africa, and Rajasthan) interference by humans in the environment of Central Asia goes back a very long way. Numerous artefacts of Mesolithic and Neolithic settlements are found all over this vast region. Centres of great civilizations repeatedly rose and fell: Nisa (Baktria), Margiana, Merve, Horesm, Bukhara, and Samarkand. Various nomadic tribes (Sarmatians, Khosars, Huns, Bulgars, Kalmyks, and Mongols) successively conquered the area until the Middle Ages. Except for the large oases alongside the major river valleys, where intensive irrigated agriculture was dominant for millennia, the most important human interference with the desert and semi-desert biomes is grazing. The domestic herds are generally dominated by sheep, but camels and goats are also present.

The effects of grazing by domestic animals differ from those of wild herds. The domesticated herds move slowly and do not stray great distances from waterholes. They cause stress on pasture around watering places, while the areas further away remain almost undisturbed. The result is concentric annular vegetation around watering places, with increasingly degraded vegetation as one approaches the centre. Around the waterhole itself, where the animals remain the longest, there is no vegetation at all, and the soil is overfertilized by animal excrement. The negative effect of this overfertilization remains noticeable for many years after the watering places are abandoned. The destruction of plant cover usually leads to the formation of barchan fields and chains in the areas of sandy, erodable soils. In the desert zone, around a barchan field, one can usually find vegetation cover, composed by such species as Aristida and Astragalus (i.e., plants not consumed by livestock). The normal composition of the vegetation cover, typical of this zone, may be found only at a great distance from the wells. In the semi-desert zone the perennial grasses disappear from the vegetation cover, while the number of annuals and biennials, especially Poa bulbosa, increase.

Grazing can exert both positive and negative effects on vegetation. Positive effects include: a slight loosening of the soil surface; promotion of seed-setting by plants, and pressing of seeds into the soil by hooves; and fertilization of the soil through excrement. These positive effects are noticeable only with an intermediate grazing intensity. In contrast, with overgrazing, the soil is loosened too much and is blown away and barchan fields develop. With undergrazing, the loosening is too little and unwanted mosses take over the area. Similarly, the pressing of seeds to the optimal depth occurs only with a moderate numbers of animals per hectare of pasture. This intermediate disturbance model is discussed in detail by Huston (1994).

Under rational use with moderate occupancy, optimal utilization could be sustained without damaging the plant cover of the pastures. Short grazing during each season most closely resembles the original use by the wild herds, which constantly change the location and never remain for very long at any one place.

During the Soviet period, the major economic effort was focused on irrigation and monoculture development with extensive cotton plantations, especially in the southern desert biome, and cereal cultivation in the semi-desert. Irrigation of the Golodnaya Steppe in Uzbekistan, massive afforestation measures in the northern Caspian, or construction of the Karakum canal, crossing the entire territory of Turkmenistan, are certainly among the most impressive projects of the 20th century in this area. However, the euphoria of the 1960s-1970s about the achievements in land amelioration and impressive agricultural statistics, was sometimes superseded by deception caused by massive spread of soil salinization and degradation, river depletion, and many other negative environmental processes.

The Institute of Deserts of the Turkmen Academy of Science carried out a detailed and fundamental study of human impacts and desertification processes in Central Asia (Map of Desertification Processes and Risk, 1989). Below, Nick Middleton discusses the region of the deepest environmental crisis in Central Asia — the degradation of the Aral Sea.

<<< Biota and Soils | Biomes & Regions Index | The Mountains of Northern Russi: Introduction >>>

 

 


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