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<Forum on the Caspian, Aral and Dead Seas-Perspective
of Water Environmental Management and Politics>

<Symposium on the Aral Sea and The Surrounding Region
-Irrigated Agriculture and the Environment>

Anthropogenic Dynamics of Vegetation of Central Asia

Natalia P. Ogar
Research Institute of Botany, Kazakh National Academy of Sciences

Anthropogenic dynamics of vegetation caused by economic activity have been illustrated on the examples of Kazakhstan and Mongolia. This process is accompanied by simplification of structure, loss of biodiversity, decrease of productivity, disturbance of functioning and loss of resource potential of the vegetation. Vegetational cover is a very important water balance stabilizing factor in the deserts. Successions of vegetation in different types of deserts in the course of pasturing have been analyzed. Particular attention has been paid to the region of Aral sea.

The central part of the Asian subcontinent is characterized by unique environmental and climatic conditions and is represented by a consecutive spectrum of deserts of subzonal types which are combined by the term "arid zone". This territory with a sensitive ecological balance dramatically and rapidly shows causal relationships between environmental and anthropogenic stimulants, derived from human activity processes In absence of a purposeful ecological policy in Central Asian countries and due to extensive, resource consuming economics in the second half of the 20th century, degradation of the ecosystems over a vast territory has occured. Modern vegetational cover is an indicator of anthropogenic disturbance of ecosystems. Economic activity transforms natural vegetational cover and results in formation of unstable anthropogenic modifications of the plant communities, simplification of their structure, decrease of their biodiversity and productivity, disturbance of their functioning and loss of their resource potential.

Modern anthropogenic dynamics of the vegetation show a destructive trend in most of the territory of the Asian arid zone. The factors of anthropogenic transformation of the vegetation are defined in order of priority as follows:

1) pasturing (grazing, overgrazing) is the most widespread factor with different rates of stocking and impact on the vegetation.

2) economic use of the forests (deforestation of mountain coniferous forests, elm and poplar gallery forests, tugai forests, Haloxylon desert woodlands and uprootings of the shrub and semi-shrub formations for construction and heating) has a spread type of influence and causes different degrees of environmental disturbance.

3) agriculture (areas of un-irrigated cultures, ploughed fields, fallow lands) has a spread type of influence and completely removes the natural vegetational cover;

4) transport (network of roads) has a linear-local and most irreversible type of influence and completely removes vegetation;

5) construction and industry (construction engineering in urban and rural areas, industrial engineering, thermal power stations, electricity transmission lines and military units) have a local irreversible type of influence which causes strong disturbances or complete removal of the vegetation leaving a wide area chemically polluted.

6) hydro-technology (storage lakes, dams, irrigation outflow, canals, fields with irrigation net) has a local spread type of influence and results in fundamental change of the vegetation.

7) cattle-breeding (stalled keeping of cattle and processing of cattle-breeding products) results in heavy trampling of the vegetational cover on narrow local areas of 2-6 km in diameter.

8) mining (extraction of minerals including mines, open-pit mines, open-cast mines, waste banks, dumps,oil and gas installations, oil and gas pipelines) results in strong disturbances of the vegetation in local areas of 100-200 km in diameter with contamination of vegetation by highly toxic compounds.

Analysis of the anthropogenic dynamics of the vegetation of the Asian arid zone has been made taking Kazakhstan and Mongolia as an example. The zonal vegetation continuum of the different types of deserts as well as the structure of altitudinal zonality of the arid mountains are completely represented on the territory of these countries. According to botanical-geographical regionalization this region appertain to Iran-Turanian (Kazakhstan) and Central Asian (Mongolian) subdistricts of Sakhara-Gobian district (Rachkovskaya,1993).

Vegetational cover of the Kazakhstani desert is characterized by a disturbance ranging from average to high. Natural communities occupy small areas of territory. Because of the high population density this region is influenced by several anthropogenic factors and their total effect hasten the degradation of vegetational cover.

Because of some natural and historical peculiarities, Mongolia, in contrast to Kazakhstan, is one of the exceptional regions of the Eurasian continent where ecosystems remained in relatively undisturbed conditions with a natural vegetational cover. Pasturing and economic use of forests are the key and common factors of vegetation degradation in these countries. Vegetational covers of the desertificated steppes and steppificated deserts which occupy the plains and foothills have undergone the highest rate of stocking. Intensive agricultural use of these lands caused natural vegetation to remain only in local areas worthless for any economic use. As a result of long term overstocking, communities with dominance of Artemisia species and graminous plants (Poa bulbosa, Stipa species) were replaced by monodominant ruderal communities of Ceratocarpus utriculosus. Foot hill pastures of Tien-Shan, Dzhungarsky Ala- tau, Karatau are the areas of ecological disaster. Vegetation of the sands of both Turanian and Central Asian deserts are subject to the significant negative impact of over stocking.

In the middle and southern parts of Turan, shrubs and Haloxylon trees do not recover and the herb layer is entirely obliterated if subjected to over stocking. Species characteristic for the degradation processes such as Calligonum sp., Ammodendron conolly, Astragalus paucijugus, Goraninovia ulicina invade the sites of deflation and erosion originated by destructive effects of overstocking on the structure of sands (Kurochkina, 1978). Communities of the clay deserts on brown and grey-brown desert soil with dominance of different species of Artemisia, Anabasis salsa and Salsola arbusculiformis (region adjacent to the northern part of the Caspian Sea, near the Aral Sea region, the Betpak-Dala desert) are more resistant to pasturing. But in the case of pasturable use over a long period of time these communities are replaced by secondary aggregations of xerophytic annuals (Ceratocarpus utriculosus, Peganum harmala). Communities lose valuable fodder herbs: Stipa sareptana, S. capillata (northern deserts) and Poa bulbosa, Rheum tataricum, Allium sp. (southern deserts). The Mongolian pastures in the northern and steppificated deserts are considerably disturbed (Ecology and wildlife management in Mongolia, 1992).

Plant communities of the northern deserts, dominated by small bunch grasses (Stipa gobica, S. glareosa, Allium polyrhizum) have no analogues. Due to the compactness of the bunches, these species are highly resistant to pasturing. But if subjected to severe impacts the bunches are destroyed, deflation processes develop and activity of digressional species increases (Artemisia pectinata, Convolvulus ammani . Foothill and aeolian (formed by wind) plains are mostly transformed by pasturing areas in steppificated deserts (Reamuria songorica, Salsola passerina, Anabasis brevifolia).

In true deserts the increment of Haloxylon-trees are considerably decreased by pasturing. Extreme arid deserts are not disturbed and are mostly represented by natural territories. Anthropogenic influence strengthens the negative effect of ecological factors by changing the structure of communities. Under overstocking anthropogenic succession has predominant significance in the dynamics of vegetation according to the following scheme: climax (natural community), a series of thinned communities with small number of species and with weeds in their composition. Further development of aridisation and disturbance of the river basin water balance are the consequences of this succession. This fact should be taken into consideration in economic planning, particularly in the Aral region. Increase of the area under irrigation in the Aral region promoted overstocking in the rest of the territory. Reversible change of the vegetation takes place in case of a moderate rate of stocking and irreversible change in case of overstocking. Any transforming community initially passes through the reversible stage and then reach the irreversible stage. The degree of changes in a community structure, the age composition of coenotic population of the dominants and the presence of seed stock in soil layers are the factors of reversibility.

Pastures are the most valuable reversible resource in the arid zone. The contemporary state of the pastures show evidence for the need to take urgent measures to revegetate, improve and protect. Dynamics of vegetation in the regions of ecological disaster have the potential for catastrophic change. Near the Aral region is one such region.

Degradation and desertification of the vegetational cover of the Aral surroundings are caused not only by exsiccation of the Aral sea, but also by irrational economic use of the nature in this region.

New ecosystems have been formed on the exsiccated sea bed of the Aral sea. Pioneer plants here are the annual hyperhalophytes: Atriplex fominii, Salicornia europaea, Suaeda arcuata (Aral sea). Succession of vegetation has a syngenetic (primary) nature and develops according to three main directions: halophyte, meadow and psammophyte directions. Competition between species of the different biomorphes (life forms), life cycles and ecologies is the mechanism of succession. According to the succession rate, successions are divided into four types: catastrophic, very rapid, rapid and long term successions. Since the structure of communities is in progress, they are unstable and sensitive to any, even light, anthropogenic influence. Similar dynamics of vegetation take place at the exsiccation zone of the Balkhash lake. In spite of the inevitable regional differences between the Aral sea and Balkhash lake, the short-lived aggregations of annual species such as Chenopodiacia sp. (Aral sea) and Phragmites australis (Balkhash lake) predominate in the first decade on the exsiccated areas. Afterwards active invasion slows down and is interrupted by a long biological pause which may last for several years. This biopause is then followed by a slow stage of desert colonization of perennial plants germinating from seed stock of zonal and coastal vegetation.

The most intensive dynamics of vegetation take place at the deltas of desert rivers (Ili, Chu, Syr-Dar'ya, Amu-Dar'ya). Profound changes in ecosystems of delta plains have followed the limitations of river runoff after hydrotechnical construction. Water, sediment and biogenic runoffs have been considerably reduced. Dynamics of alluvial processes at bottomlands and conditions of soil and vegetational cover have been disturbed. Desertification develops at the areas which became free from the influence of flood water. Character, rate and direction of the successions are caused by hydrodynamical, geochemical and salting processes and the arid climate. Successions develop rapidly and often, and are catastrophic in character. Meadow and tugai (woody and shruby) types of vegetation are replaced by desert types in 5-10 years. This leads to a decrease of coenotic diversity of 20-50 times, reduction of biological productivity of 15-20 times and economic productivity of 30- 35 times.

Successions show halophytic (Syr-Dar'ya, Chu rivers) or xerophytic (Ili river) trends depending on the degree of salinization of soils and ground-water. After many years of study of the dynamics of soil and vegetation we have determined the stages of desertification defining the rate and trend of successions (Plisak, Ogar, 1989).

Along with the desertification processes, underflood and swamping takes place on river deltas, coasts of storage lakes and at areas of irrigated agriculture. These processes have negative consequences because of progressing salinization.

Dynamics of vegetation depends on the regime of dam outlets from storage lakes as well as from the regional peculiarities such as physical and geographical conditions and economic use. Irreversible successions are generated by the change of environmental conditions of ecotope (habitat). Vegetational cover changes radically depending on the level of the type of vegetation: zonal vegetation is replaced by halo-hydro and halo-mesophytes. Successions are also catastrophic in character: composition completely changes in 4-6 years (Plisak, Ogar, 1992).

Similar dynamical processes are observed on the coastal area of the Caspian sea in recent years.

But underflood conditions seem to be according to the natural process related to the new transgression of the sea. Aggregations are composed of Salicornia europaea, Phragmites australis forms on the areas of previous halophyte shrub and semi-shrub communities. Because of the progressive rise of the sea level, they exist no longer than 1-2 years and then disappear under the water.

The characteristic feature of ecosystems of super arid habitats is the incomplete formation of floristic composition and structure. As a result they are unstable in space and time making these territories very vulnerable in the course of their economic use.

Disturbance of the vegetational subsystem leads to imbalance and instability of natural ecosystems of different classes and, finally, promotes aridisation of the climate and soils, as well as negative natural processes and phenomena (desertification, salinization, dust storms, mud-streams) up to ecological disasters.

References:

Kurochkina, L.L. (1978) Psammophilous vegetation of Kazakhstani deserts. Alma-Ata, Nauka, 271 p.

Plisak, R.P., N.P. Ogar and G.M. Sultanova (1989) Productivity and structure of desert zone meadows. Alma-Ata, Nauka, 186 p.

Plisak, R.P. and N.P. Ogar(1992) Influence of straggle lakes of the arid zone on vegetation. Alma-Ata, Gylym, 230 p.

Rachkovskaya, E.I. (1993) Vegetation of Gobi desert of Mongolia. Sankt-Petersburg, Nauka, 134 p. Ecology and wildlife management in Mongolia. (1992) Transactions, Puschino, 228 p.

Succession of Phragmites australis community in the course of desertification

Desertification stages of the vegetation of delta plains of the arid zone (Syr-Dar'ya, Illi, Chu rivers).

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