ECOLOGY-GEOGRAPHICAL ESSAY ABOUT STEPPES OF NORTHERN EURASIA (Translation of M.A. Shahgedanova)

 

A.A. Chibilyov

Institute of Steppe of the Urals Branch of RAS 460000 Orenburg, Pionerskaya st., 11, Russia

 

INTRODUCTION: MAIN FEATURES AND DEFINITIONS

Treeless areas, termed steppes, occupy vast areas between boreal forests and temperate deserts in Eurasia. There are many definitions of steppes. For example, Allan (1946) provides fifty four definitions of this term. Stamp (1961) defines steppes as 'mid-latitude areas dominated by herbaceous vegetation and termed locally steppes, prairies, pampas, high veldts, downland, etc.'. A more precise definition of steppes is offered by geobotanists who define it as a type of vegetation, represented by communities of drought- and frost-tolerant perennial herbaceous species with a dominance of sedges (Poaceae) and, less commonly, galingales (Cyperaceae) and bulbs (Alliaceae).

The main features of the temperate steppes are a continental climate, the absence of trees on watersheds, and the dominance of sedges on black and chestnut soils. Steppes extend as a continuous belt from the plains adjacent to the Black Sea to Western Siberia and become fragmented east of the Altay because of the mountainous character of the terrain (Figure 1). Steppe is the main biome located between the humid landscapes of the boreal forests and the arid environments of deserts. The forest-steppe ecotone occurs between steppes and forests in the north while semideserts form a transition from steppes to the desert environments. Forest-steppes have a more humid climate than steppes and in their natural condition represent a mosaic of meadow-steppe vegetation and woodlands. It is the forest-steppe that serves as a demarcation line between humid and arid environments and here annual precipitation and evaporation are approximately equal. The forest-steppe extends as an uninterrupted zone from the Carpathian foothills to the Altay and, similarly to the steppe, becomes fragmented further east. Semi-deserts are distinguished by a more arid climate than the steppes and the domination of the communities by species of the generus Artemisia and sedges. This zone extends from the lower course of the Volga to the upper course of the Irtysh and occupies a considerable part of Central Kazakhstan.

Steppes and forest-steppes have been transformed by human activities more than any other part of Northern Eurasia. In the European part, over 60% of the steppe territory is now occupied by arable land and in the forest-steppe natural woodlands have been mostly cleared. It is fair to say that, with the exception of rather small protected areas, the biogeography of the European steppes and forest-steppes is now cultural rather than natural. The development of the Asiatic steppes began later and their transformation has not gone as far as in the western part of the region. However, in many regions original ecosystems have been transformed by pastoralism and in the late 1950s vast areas in Southern Siberia and Northern Kazakhstan were turned into arable fields in the course of one of the largest Soviet undertakings ever, the Virgin Land project. Because of it, this chapter emphasizes the human transformations of the environment and adaptations of various components of the environment to human pressure rather than approaching the steppes and forest-steppes of Northern Eurasia from the perspective of traditional biogeography.

CLIMATE

The location of the Eurasian steppe biome coincides with the zone of high atmospheric pressure and, despite the differences in climates of the continental steppes and those located closer to the coast (for example, southern Moldavia receives about 410 mm of precipitation per annum while Tuva has only about 215 mm), moisture supply is insufficient across the biome. Evaporation exceeds precipitation by a factor of 2-3. Typical are the distinct June (July-August in the Dahurian steppes) maximum in precipitation and its high interannual variability. An important climatic feature is the small thickness of snowcover and the re-distribution of snow by wind. Snow is often blown off the watersheds and accumulates in topographic depressions, shrublands and woodlands, which causes strong spatial differences in soil climates. The temperature gradient changes eastwards as a result of increasing continentality. The mean annual temperatures change from approximately 9°C in Moldavia to about -6°C in Tuva and the mean annual temperature amplitude increases from 27°C to 53°C.

All biotic components of steppes are closely controlled by climate and change from west to east in response to the increasing continentality. This is expressed in b oth, the changing structure and floristic composition of vegetation (the replacement of the European species' by the Kazakh and then Mongolian species) and in the changing productivity of ecosystems, the ratio between the above-ground and below-ground biomass, and the thickness of the humus horizon (Ziotin, Chapter 6; Mordkovich, 1982).

SOILS

The soils of steppes and the factors involved in their formation are discussed in Chapter 4 and here only a brief discussion follows. Two types of soils are typical of the steppe and forest-steppe biomes: chernozems or black soils and kashtanozems or chestnut soils (Table 1). Chernozem is one of the most fertile soils on the planet. In Northern Eurasia, chernozems occupy about 1.9 million km2. Many prominent scientists researched the origin of chernozem and linked-it to the rich herbaceous vegetation typical of steppe and meadow-steppe (Rupreht, 1866; Dokuchaev, 1883; Kostychev, 1937). About 1-2 kg m2 of dead phytomass is produced annually and about a half of it is contributed by the below-ground parts (Alehin, 1934; Titlyanova et al, 1983). The organic matter does not, therefore, concentrate on the surface as litter but is more deeply and evenly distributed through the soil profile due to the extensive and deep root systems of the plants. The most favourable conditions for the development of chernozems occur in the southern forest-steppe where high phytomass reserves coincide with the optimal thermal and moisture regimes. Thick chernozems dominate in this region. Northwards, a more humid climate results in leaching of primary minerals and podzolization of soils. Southwards, a moisture deficit causes a reduction in phytomass and the supply of organic matter to the soil, which leads to the formation of soils less rich in humus and nutrients. The group of chernozem soils, therefore, consists of a number of sub-types which exhibit a zonal distribution.

Most fertile are typical chernozems whose humus contents can be as high as 15% (Table 1). Normal chernozems, which develop in the northern steppe, are distinguished by a less developed humus horizon and the content of organic matter does not on average exceed 6-9%, although in soils with a fine grain structure it can be as low as 4-5% (Chesnyak et al, 1983). Southern chernozems develop under the Stipa-Festuca vegetation communities in the southern steppes. They are characterised by a smaller thickness of the humus horizon, which varies between 25 and 70 cm. Meadow chernozems develop both in the steppe and forest-steppe biome in environments with a higher moisture supply such as poorly drained watersheds, in topographic depressions and stream valleys. Meadow chernozems are very similar to chernozems and the major distinction is that the content of organic matter in meadow chernozems is higher and, consequently, the humus horizon has a darker colour (Zamotaev, Chapter 6).

The changes in soil profile also occur from west to east, reflecting the increasing aridity and continentality of climate. Thickness of soil cover decreases substantially. In the Black Sea steppes, soil profiles are about 200 cm deep while eastwards they become progressively thinner, reaching 50-60 cm in the Transvolga region and 30-40 cm in Kazakhstan. The occurrence of solonets-like soils also increases from west to east

ENVIRONMENTAL FACTORS CONTROLLING STEPPE AND FOREST-STEPPE PHYSIOGNOMY

The debate on the origin of steppe and forest-steppe has a long history. Many scientists attempted to explain the main physiognomic characteristic of these landscapes - the absence or lack of tree vegetation. The first hypothesis dates back to the eighteenth century when Pallas (1770) suggested that trees were destroyed by man. Later the anthropogenic hypothesis was supported by Palimpsestov (1890) and Taliev (1905). A century ago, the idea of climatic control was put forward by Vysotsky (1905) who suggested that the climate of steppes, with its frequent dry winds and insufficient moisture supply, prevents the development of forests. In the  monograph  'Grasslands  of the Northern Hemisphere1 Krasnov (1894) explained the lack of tree vegetation by the flat topography of the steppes, which resulted in poor drainage which was unfavorable for tree growth. In his view, climate merely controlled floristic composition of steppe vegetation. Tanfiliev (1894) saw the high salinity of soils as the major factor opposing the development of forests. A prominent soil scientist, Kostychev (1937), advocated the ecological view according to which tree vegetation could not withstand the competition with grasses because their deep and extensive roots form a thick turf layer. All these environmental factors exert control over the physiognomic character of steppe vegetation, complimenting each other's influence. As suggested by Milkov (1977): "The treeless character of steppe vegetation is a zonal phenomenon determined in the first place by dry climate. This climate, unfavorable for tree growth, provides a background for the salinisation of soils, the domination of herbaceous species and other factors". Speaking of the treeless character of steppe landscapes it is important to keep in mind that woodlands commonly occur in steppes, including even its southern sub-zone.

The development of steppe landscape began before the onset of glaciations. In the Neogene subtropical forests were replaced by grass communities as a result of increasing aridity (Velichko and Spasskaya, Chapter 2) and the precursors of modern steppes, Neogene savannas, developed (Neishtadt, 1957; Milkov, 1977). The formation of steppe flora occurred during the glacial periods. The contemporary borders of the Northern Eurasian steppes formed in the early Holocene. In Europe, this time coincides with the beginning of the latest interglacial.

The character of steppe landscapes shaped and strongly influenced the occupations and life-style of its nomadic population, skiffs and sarmats until the fourth century AD and later turcic peoples. Later, however, it was humans who to a great extent controlled the development of steppe and forest-steppe landscapes. In the late Holocene, the areas occupied by woodlands decreased significantly under the human influence and much of the territory was transformed by arable agriculture. Having played an important role in the history of humankind, forest-steppes and steppes were the first biomes whose original character has been dramatically altered and in the European territory almost completely changed.

CLASSIFICATIONS, ZONAL AND PROVINCIAL DIFFERENCES

Steppes extend across the European territory, Western Siberia and Kazakhstan as a continuous, 200-600 km wide belt. In Southern Siberia, steppe vegetation occupies the intermontane depressions and plateaus. The alpine steppes occur in the southern Urals, Altay, Caucasus and in the mountains of southern Kazakhstan and Central Asia. Fragments of steppe vegetation widely occur in the ecotone of semi-desert.

Steppes and forest-steppes, developing on the plains, are subdivided into a number of subzones according to the dominant types of soil and vegetation (Table 1). The most commonly used classification of steppes distinguishes three sub-zones: northern, typical (or true) and southern (or dry) (Chibilyov, 1990, 1992). The subzone of typical steppes occupies the middle position between the northern and the southern steppes. Zonal soils are southern chernozems and species in the genera Stipa and Festuca dominate. The northern steppe is charaterised by the development of polidominant herb-grass communities on the thick chernozems, while in the southern steppe species of Stipa and Festuca dominate on the dark chestnut (kashtanozem) soils. Similar differentiation occurs in the forest-steppe which is also known as meadow-steppe (Table 1). In its natural condition, it represents a macromosaic of woodlands and open landscapes. Since it is distinguished by lower aridity of habitats, herbs are common here while only the most moisture-loving species of sedges occur.

Apart from zonal divisions, two latitudinal sectors are distinguished within the steppe and forest-steppe zones: the East European and the Western Siberian - Northern Kazakhstan (Milkov, 1977; Chibilyov, 1990).

The East European sector extends in a sub-meridional direction from the south-west to the north-east. As aridity increases, at a latitude where steppes occur in the Ukraine, semi-deserts develop in the Transvolga region. A number of provinces, shown in figure 2, are distinguished within the East European sector (Milkov, 1977; Chibilyov, 1992). In comparison with the Asiatic steppes, the climate of the European steppes is less continental. There are many European species in both flora (Stipa ucrainica, Bromus riparius) and fauna (the European ground squirrel). Typical of the European steppes are shrublands formed by Caragaria frutex, Cerasus frucitosa and Prunus stepposa. Woodlands of the forest-steppe, riparian forests and isolated woodlands, which often develop on watersheds in the steppe biome, are formed by Quercus robur, Tilia cordata, Acer platanoids and Corylus avellana. Composition of woodlands in the forest-steppe (which is the same as of deciduous forests) is discussed in depth in Chapter 10.

Yet, most of the European steppe and forest-steppe is not represented by natural ecosystems. The original steppes have been transformed into agricultural lands almost entirely and at present fragments of pristine steppe occur only in nature reserves and in the areas were dissected topography prevents development. Only the steppes of the Transvolga region have been less affected and the unploughed steppes occupy between 10 and 23% of the area (Chibilyov, 1992).

The West Siberian - Northern Kazakhstan sector extends between the Urals and the Altay (Figure 2). Continetality of climate is higher in comparison to the European sector, the amount of precipitation is lower, while the period of snow cover is longer. Stony and saline soils are more widespread while both the proportion and quality of chernozems are lower. A distinguishing feature is the occurrence of numerous lakes. Asiatic species (Stipakorshinski, S. kirghisoruna, Artemisia frigida) dominate. The broadleaf tree species disappear from woodlands which are formed by Betula and Pinus. The share of unploughed steppe, most of which is used as pastures, reaches up to 35% of the area in Northern Kazakhstan (Chibilyov, 1992).

East of the Altay, steppes develop as fragmented areas in the intermontane depressions of Southern Siberia and the Transbaikal region. Climate is strongly continental with low precipitation and extremely harsh winters (Table 2). Even in comparison to Kazakhstan, soils are poorly developed. The vegetation of the Eastern Siberian steppes is similar to that of the Mongolian steppes with a dominance of Stipa capillata and the absence of ephemerals and ephemeroids.

In response to the harsh environmental conditions, species richness declines towards the centre of the continent. While over 200 herbaceous species occur in the meadow steppe of the East European plain, only 55-80 species are typical of Western Siberia and 40-50 of Khakassia. Similarly, dry steppes are represented by 150 herbaceous species in the Askania Nova nature reserve in the southern Ukraine while in Khakassia only 30-35 species occur. This, however, does not imply that the Asiatic steppes are impoverished but rather shows that the European steppes are enriched by meadow species. Traditionally the proportion of xerophilous species in the floristic composition of steppe vegetation has been used as an indicator of a 'true nature' of steppes. The participation of such species is much higher in the east. Thus, in the meadow steppe in the southern Urals xerophilous species account for 60% of flora while in the region of Kursk in Central Russia they represent only 5-12% (Chibilyov, 1992). The typical steppe species are better adapted to harsh environmental conditions and, therefore, ecosystems dominated by such species are more stable. One of the major adaptations of steppe vegetation is the extensive and deep root system of grasses. Root phytomass progressively increases eastwards. The traditional question whether "steppe ecosystems advance to the forest biome or forests advance to the steppe" does not occur with respect to the Siberian steppes (Titlyanova et ai, 1983). The vegetation of the Asiatic steppes, represented by xerophilous plants whose deep and well-branched roots form extensive turf, marginalises the competition of woody species. In contrast, ecosystems of the European steppes, dominated by less drought-resistant grasses and herbs, are less capable of successful competition with woody species.

BIOLOGICAL DIVERSITY

Specific features of steppe flora

The biological diversity of natural steppes is extremely rich both with respect to number of species and life-forms. Between 37 and 56 species per m2 occur in the protected steppes of the Kursk and Voronezh oblasts in Central Russia and up to 80 species are found in the meadow-steppe of the region (Alekhin, 1986). There are a number of specific features distinguishing steppe vegetation. Firstly, steppe ecosystems are composed of grasses among which xerophilous sedges predominate. Secondly, most plants of the steppe have a well developed fibrous root system with a large surface area, a characteristic which is important under the condition of low soil moisture. Biomass of the below-ground parts considerably exceeds biomass of the above-ground parts and is concentrated mostly in the uppermost 50 cm in the humus horizon of soil. Thirdly, dead parts of the steppe plants quickly decompose down to mineral components.

In response to the dryness of steppes, plants have developed many adaptive features. One of the adaptations, an extensive and deep root system, has already been discussed. Others include the narrow shape of leaves and the bunch (tussock) form of plants. Narrow folded leaves (1.5-2 mm wide) reduce moisture loss through transpiration and allow grasses to tolerate hot and dry weather. The bunch form allows the accumulation of snow and dust and, therefore, plants receive more moisture and nutrients. The base of tillers in bunch-grasses is positioned rather deep in soil, thus protecting them from trampling by ungulates. Light colours, typical of the steppe plants, help to reflect sunlight, thus protecting plants from overheating.

The open character of the steppe landscape and frequent strong winds have led to the development of peculiar adaptations with respect to the dissemination of seeds and fruits. One of the most interesting adaptations is the so-called 'tumble weed'. By the time when seeds are fully ripe, spherical inflorescences breaks off at the root collar and, steered by the wind, roll across the steppe, scattering seeds. Grambe tatarica, Gypsopmilapaniculata, Ceratocarpus arenarius, Phlomis pungens, and Salsola belong to this group of plants.

Before the development of agriculture, zonal steppe vegetation was dominated by the turf-forming grasses such as Stipa, Festuca, Koeleria, Poa, and also Carex. Widespread are ephemeroids, i.e. plants which develop in spring when the soil is wet and flower and produce seeds by the beginning of the dry period (this is yet another adaptation to the dry conditions). Typical ephemeroids of steppe are Tulipa, Iris, Gagea, Adonis spp. and some species of Astragalus. However, under conditions of insufficient moisture supply, the distribution and character of vegetation are strongly affected by microrelief and the lithology of soils and rocks. Meadow vegetation often develops in topographic depressions. Variations from the zonal vegetation occur in sandy and stony and gravely soils. The sandy steppes, whose origin is linked to aeolian and river sands, occur in almost all provinces. Vast areas are occupied by sandy steppes in the lower course of the Dniepr (the so-called Aleshkovskie sands), in the basin of the river Don and on the watershed of the Volga and the Ural. Psammophytic vegetation dominates these landscapes. The most typical species are Elymus giganteus, Gnaphaliwn arenarium, Stipa rubens and Koeleria.

The stony and gravely steppes are typical of the Southern Urals, Central Kazakhstan, the Altay and Sayan mountains and the Transbaikal region. Fragments of the stony steppes also occur in the Ukraine (in the Donetsk upland and Crimea). Soil cover is poorly developed in the stony steppes and erosion rates are particularly high. Compared to other ecosystems, stony steppes are less productive. However, the share of endemic plants is much higher than in zonal steppe ecosystems because stony soils served as a refugium for many species during unfavorable climatic epochs. According to Gorchakovsky (1997), the stony steppes are not just a petrophilous type of zonal steppe but an ancient floristic complex. Endemics and relics include petrophilous species especially of the genera Astragalus, Oxytropis, Hedysarum, Miniartia, and Dianthua.

The character and distribution of vegetation in steppe and semi-desert is affected by the salinity of the soils. Three groups of steppe ecosystems are distinguished with respect to salinization: calcareous and those developing on solonets and solonchaks. On calcareous soils, the floristic composition is shifted towards xerophi-lous species such as Stipa capillata on calcareous chernozems and 5. lessingiana on calcareous dark-chestnut soils. In contrast, Stipa is practically absent from the solonchak steppes, where species of Artemisia, Grinitaria and Kochiaprostrata widely occur. Silaum besseri, Galatella and Artemisia dracuncuhis develop on the well-moistened saline chernozems. The flora of the solonchak steppes, which are widespread in the south of the biome, consists almost entirely of halophytes such as Salicomia, Holocnemum, Suaeda and Salsola.

Tree and shrub vegetation in steppes

The steppes and even the semi-deserts of Northern Eurasia are not completely treeless. A typical feature of steppes is the occurrence of shmblands which are composed of Prunus fruticosa, P. spinosa, Amegdalus, Caragana, Spirea and Rosa. Apart from the open.steppes, shmblands often form a dense belt surrounding woodlands. Isolated woodlands occur mainly in the specific habitats characterised by higher moisture supply and often represent peculiar oases of unaltered nature in the steppe biome. Typical woodland ecosystems include Quercus woodlands on the watersheds, Betula and Populus tremula woodlands developing on sandy soils and in the topographic depressions, open woodlands composed of Pinus silvestris, which occur on granite rocks, and riparian forests comprised by Ainus ulnutinosa and Populus spp. Ravines, which are a typical feature of steppes, are mostly covered by woody vegetation, among which Quercus, Tilia, Acer, Fraxinus, Ulmus, and Betula predominate. The composition of woodlands changes from west to east. In the European steppes, Quercus is the dominant tree species while east of the Urals Betula, Pupulus tremula and Pinus silvestris occur. The occurrence of patches of woodland in steppes often makes it difficult to distinguish between steppe and forest-steppe, particularly in the context of the complex topography of Southern Siberia and the Baikal region (Bannikova, 1998).

Fauna

A characteristic feature of the animals of the steppe and forest-steppe zones is that most of them (for example, wolf, fox, elk, badger, wild boar, roe deer, grouse) have polizonal areas of distribution. The number of endemic species is much lower than in the neighboring forest and desert biomes. Thus mammal species endemic to the steppe biome account only for 30% of all mammal species that occur in steppe, while in boreal forests and in deserts about 70% of all mammals are endemic to these biomes. This is because in the steppe and forest-steppe there is a large variety of habitats ranging from wetlands to semidesert and from woodlands to sandy or stony steppes. Ungulates and rodents dominate among vertebrates. According to Formozov (1981), ninety two species of mammals occur in steppes at present, not including the long extinct tur, the European wild horse and bison. The animal population of the steppe is highly variable both in terms of number of individuals and diversity of species. Some animals (e.g. saiga, the Asiatic wild ass, bustard) migrate to the steppe seasonally, some rodents (ground squirrel, marmot) are 'active' only for a few months of the year and others (e.g. griffon) reproduce only in favorable years.

The animal population is also sensitive to ecological factors and the interannual variability in environments which is so typical of the steppe biome.

As the main feature of steppes is the open character of the landscape, many species developed various adaptations to existence in open spaces. Thus many rodents inhabit the below-ground part of the ecosystem and form colonies. Out of ninety two species of steppe mammals, seventy two dwell in the soil (Formozov, 1981). Life in colonies allows rodents to move safely across large areas. For example, the population density of marmots often reaches 20-30 individuals per hectare. Burrows are located close to each other and connected by passages along which marmots can move very fast. Grazing marmots always closely observe each other and quickly react to each other's warning signals. This is a very effective system of protection which makes it difficult for carnivores to attack marmots. Many rodents feed on the below-ground parts of plants, i.e. rhizomes, bulbs and tubers, which are particularly well developed in the steppe biome. Fifty three species that inhabit burrows are active all year round and fifty of these species accumulate stores for winter. For example, steppe pika accumulates hay in the early summer when plants have the highest nutritional value. It stores hay in burrows, hollows or on the surface, forming small haystacks.

Burrowing activity of rodents is an important factor in the formation of soils (Dokuchaev, 1883; Grinnel, 1923), the nature of microrelief and the vegetation in all types of steppe ecosystem from the meadow steppes in the north to the desert steppes in the south (Formozov, 1981). The interrelationships between vegetation and the animal population were studied in detail by Lavrenko (1952) who suggested that rodents (especially marmots and the ground squirrel) have a considerable influence on the stmcture of steppe vegetation and attributed the complexity and irregularity of vegetation patterns, observed across vast areas in pristine steppes, to the burrowing activity of rodents. Ungulates of the steppe are gregarious and are able to move fast in the search of food such as, for example, saiga, a typical species of the Kalmyk, southern Urals and Kazakhstan steppes. The European wild horse (now extinct) and the Asiatic wild ass (at present not found in the steppe) used to form herds of 50-100 and sometimes up to 1000 individuals. Well known are the effects of ungulates on the development of steppe ecosystems. Research conducted by Lavrenko (1980) in protected steppes has shown that the true steppe 12 ecosystems dominated by bunch grasses can exist under conditions of moderate grazing.  The absence of grazing results in the accumulation of dead phytomass, a changing microclimate of the plant canopy and the replacement of grasses by rhizomatous species and shrubs, while extensive grazing leads to a decline in the abundance of forbs and later species of Stipa followed by an increase in species of Festuca (Chibilyov, 1990; Lavrenko and Karamysheva, 1993).

The transformation of steppes has caused an irreversible decline in the diversity of animals. In prehistoric times, the population of saiga and Persian gazelle exceeded 10 million and 5 million individuals respectively, while the population of wild horse and tur accounted for dozens of millions (Mordkovich, 1982). The development of pastoralism and agriculture over the 2-3 millennia destroyed the habitats of wild ungulates and most species had become extinct by the beginning of the nineteenth century. For example, the Asiatic wild ass disappeared from the Ukrainian steppes in the sixteenth century and from the Volga-Urals watershed and Kalmykya at the end of the eighteenth century. At the beginning of the nineteenth century it was still widespread in Western Siberia and Central Kazakhstan. However, already at that time the boundary of its distribution was rapidly receding southwards and by the 1930s it had become extinct in the steppe biome. Well documented is the extinction of the European wild horse, hunted widely both for meat and skin and because it often distracted females from the domestic herds. Its population had been critically depleted by the beginning of the nineteenth century and the last individuals are known to have been killed in the 1870s (ironically in the region of the now most well-known steppe nature reserve Askania Nova) which marked the end of the European wild horse as a biological species. Among ungulates, only saiga and Persian gazelle still occur in the wild. However, by the beginning of the 1990s saiga had diverted its migration routes away from the northern steppes and Persian gazelle has not been seen in the agricultural regions for many years. Other species, including such typical bird species of the steppe as the great and little bustard, have been affected by both development and hunting. Nature reserves could play an important role in the protection of the steppe species. However, protected areas account for a rather small territory (Tishkov, Chapter 24). After the Askanya Nova nature reserve was established in 1898 in the southern Ukraine, no other large reserves capable of protecting typical wild life have been established in the steppe and forest-steppe zones.

The expansion of agriculture has affected both the environmental characteristics of habitats and species selection and has led to the formation of a new fauna which did not exist in prehistory. The modern fauna of the steppe biome comprises domestic animals and species that have adapted to agricultural landscapes. This fauna is species poor and its composition is uniform across the biome. Typical species include ground squirrel, common hamster, European hare and small birds feeding on grain and insects such as locust.

ANTHROPOGENIC TRANSFORMATION OF STEPPE AND FOREST-STEPPE

Steppe is the main agricultural region of Northern Eurasia and 57% of the area occupied by chernozems is arable land (Table 2). The agricultural development of steppes has a very long history and three major phases in the transformation of steppe soils are distinguished:

development, degradation and cultivation (Kovda, 1974). In the early stages of cultivation of steppe and forest-steppe soils (the first few years after ploughing), yields are usually high. However, at this stage cycling of minerals is transformed, and a decline in the contents of organic matter, nitrogen and phosphorous and degradation of the physical and moisture properties of the soil occur. If no organic fertilizers are applied, soils degrade. The fertility of chernozems starts to decline, followed by a changing morphology (compaction) of the soil, a sharp decline in yields and their subsequent stabilization at a much lower level. Cultivation of chernozems refers to its rational and sustainable use which is only possible if fertilizers are used in order to compensate for the loss of natural fertility. The maintenance of the optimal balance of organic matter and other nutrients makes its possible to obtain high yields while preserving or even improving chernozem fertility.

Long cultivation has considerably altered the properties of chernozems and particularly their organic matter content. In the 1980s, data were published illustrating the losses of organic matter, which occurred during the last hundred years since Vasily Dokuchaev began studying chernozems (Rozanov, 1983; Rozov, 1983). Thus in 1881, the humus content in the uppermost 30 cm layer varied between 10% and 13% in the typical chernozems of the Voronezh oblast in Centra! Russia while its stock was estimated as 30-39 thousand tonnes km"2. By 1981, these values had decreased to 7-10% and 21-30 thousand tonnes km"2. The total loss of organic matter over the last hundred years was, therefore, 9 thousand tonnes km"2 in all or 90 tonnes km"2 each year. In the Stavropol region, organic matter declined at the rate of 70-80 tonnes km"2 a'J , in Orenburg oblast at the rate of 90 tonnes km'2 a" ', and in the leached chernozems of the Ulyanovsk oblast at the rate of 270 tonnes km"2 a"1. On average, the loss of organic matter over the last hundred years is estimated as 20-35% in the Black Soils region of Central Russia, Northern Caucasus and Orenburg oblast, and as 56-69% in the forest-steppe of the Volga region (Chesnyak, 1983).

Soils of the European steppe and forest-steppe are highly susceptible to the formation of gullies and erosion which in turn contribute towards the intensive loss of organic matter from soils. The physical geography of the southern East European plain (e.g. parent rocks are mainly loess and chalk; the high intensity of summer rainfall; and freeze-thaw effects) predetermines the naturally high erosion rates. However, the major cause of landscape degradation is anthropogenic and the most important is the removal of natural vegetation and cultivation of land. The elimination of shrubs and tall grasses, which delayed snowmelting in spring, minimized surface runoff and maintained high ground water levels, resulted in less moisture accumulation in soils, thereby increasing their erodibility. In addition, traditional agricultural techniques (emphasis on grain cultures in the three field system, shallow ploughing) favoured development of erosion. The origin and history of soil erosion in the southern East European plain were studied by many scientists and Stebelsky (1974; 1983) provides a good summary.

Although the chernozems of the East European plain have been cultivated since the Neolithic, there is little evidence for early land degradation. The fourteenth century chronicles only occasionally mention dust storms, and there are no reports of dust storms in the forest-steppe zone. However, land inventories compiled in the sixteenth century mention the occurrence of gullies, both active and stabilised and wooded, in what is now the Tula oblast, thus testifying to earlier periods of soil erosion (Stebelsky, 1983). During the sixteenth and seventeenth centuries, the forest-steppe and steppe were rapidly settled and extensive lands were cultivated, but it was in the nineteenth century when most of the expansion took place. Over that century, the rural population doubled from 6 to 12.8 million people in what is now the Black Soil region (Stebelsky, 1974). With no growth in industrial employment and improvements to agricultural techniques, the agrarian development placed increasing pressure on land resources. By the end of the nineteenth century, about two-thirds of the land were cultivated in the Black Soils region and the pressing need for land caused river terraces and slopes to be ploughed. Much of the rich farmland was lost to the formation of gullies and landscapes of forest-steppe and steppe zones were permanently altered (Stebelsky, 1983).

As often happens, environmental change was accompanied by growing poverty, conflict and eventually social crisis. In 1890, the Eighth Congress of Russian Naturalists and Physicians approached the Ministry of State Property with a request to fund research on gullying and soil erosion in forest-steppes and steppes. This study, completed by Masalsky (1897), revealed widespread gullying in Bessarabia (now Moldavia), Podolya, the Dniepr Heights, and the Donets Uplands, and particularly in the Central Russian Upland and the Volga Upland. The percentage of land occupied by gullies ranged between 0.5 to 25% with 3-5 % of the area being most commonly reported (The highest figures were later proved to have been overstated since not only active gullies but also ravines were included). Land owners and peasants were encouraged to take action against soil erosion. However, most did not see a connection between land use and gullies and considered soil erosion unavoidable and conservation measures too expensive (Stebelsky, 1983).

The work by Masalsky provided a considerable amount of descriptive material; the first detailed maps of intensity of soil erosion and gully density appeared a few decades later. A large expedition through the European part of the USSR was conducted between 1939 and 1941 and provided data for the first general comprehensive map of soil erosion in the European USSR. The Black Soils region of southern European Russia experienced the most extensive soil erosion. By the middle of the twentieth century, only 10% of land was not affected by gully erosion here, a medium network of gullies (0.2 to 0.4 km of gully per km2) covered about 30% of land, and a dense network (0.5 to 1.2 km of gully per km2) covered another 35% (Sobolev, 1948; Guzhevaya, 1948).

At present, landscapes of the steppe and forest-steppe biome are at different stages of anthropogenic transformation. The following categories can be distinguished: pristine landscapes; lands used for grazing with irregular arable agriculture (this land use corresponds to nomadic livestock breeding); arable lands with extensive agriculture; and arable lands with modern agriculture (Krupennikov, 1983). There are very few regions where virgin steppes occur. Perhaps, only steppes protected in nature reserves fall into this category. Nomadic land-use was typical of the European steppe until the beginning of the nineteenth century, in Northern Kazakhstan it existed until the 1950s and at present is practiced in the Altay steppes. The most typical example of extensive agricultural land-use was the infamous Virgin Land project of the 1950s, which aimed at the expansion of arable agriculture into the steppes of Northern Kazakhstan and Southern Siberia. Intensive agriculture is practised in the forest-steppe and steppe of the Ukraine, Northern Caucasus, the Black Soils region of Central Russia and the Volga region. The scale of transformation of the steppe and forest-steppe biomes is illustrated by tables 2 and 3. Thus in the Ukraine, the Black Soils region of Central Russia, the Volga region, and Kazakhstan between 74 and 91 % of flat, well drained plains is occupied by arable fields. The remaining 10-20% is usually not a natural steppe or forest-steppe but, on the contrary, anthropogenic landscapes.

MODERN STRUCTURE OF LAND USE

The land-use structure in the steppe and forest-steppe developed over centuries and agriculture has played the most important role. There are four major types of land-use (Milkov, 1973; Chibilyov, 1992). The first one, characterised by the highest degree of transformation, includes urban, industrial and agro-industrial areas and transport networks. Landscapes of this type account for 2-7% of all territory in the steppe and forest-steppe.

Because these zones accommodate large mining areas, about 200 km in Russia, Ukraine and Kazakhstan are occupied by excavated lands and trails (Mordkovich et al, 1997). The second category includes rural settlements and minor agricultural lands such as private gardens and allotments. The third and the largest group comprises arable land and pastures. It occupies between 50 and 85% of the total area in European Russia and the Ukraine, and between 30 and 55% in Northern Kazakhstan. Agriculture in the steppe zone often relies on irrigation and irrigated lands are among the most strongly transformed landscapes of this group. The fourth category is represented by natural grazing lands (transformed to various extents), hayfields and marginal lands such as ravines, small woodlands and shrublands. Lands of this type often have a mosaic distribution within the agricultural landscape and have a stabilising effect on the transformed and disturbed ecosystems. Their share increases eastwards from 5-12% in the Ukraine to 37% in Northern Kazakhstan. The fifth group comprises riparian woodlands and meadows, vegetated wetlands and large woodlands. The stabilising function of these landscapes is particularly important. Flood-plains of the large steppe rivers are important centres of biological diversity and are highly productive. They also accommodate agriculturally valuable lands which are central to the development of the region. Lands of this group usually occupy between 3-4% of the total territory.

Large areas of the steppe, to which agricultural development has never advanced, belong to the Russian Ministry of Defence. One such area, the Donguzskaya steppe, is located to the south of Orenburg and occupies 900 km2. It is the largest fragment in Northern Eurasia of the Stipa - Festuca steppe on the southern chernozems which has never been used for arable agriculture (Chibilyov, 1996; Levykin, 1997). Protected areas account for 0.3-0.8% of the steppe and forest steppe biomes. The largest protected areas are Askania Nova nature reserve (11.1 ha) in the southern Ukraine and Orenburgsky (21.7 ha) nature reserves in the Orenburg oblast (see also Tishkov, Chapter 24).

ISSUES AND PROBLEMS OF DEVELOPMENT

Overexpansion of arable agriculture

Although the modern structure of land-use is a result of the long history of development, the greatest influence has been exerted by certain socio-economic factors of the Soviet period of which state land ownership, establishment of large-scale state farms, housing policies and the development of irrigation are the most important ones. Perhaps the most drastic transformation of the steppe landscape occurred between 1954 and 1960 when in the course of the Virgin Land project 418 thousand km2 of virgin steppe was brought into agricultural production in the Transvolga region. Southern Siberia and

Northern Kazakhstan and three million people migrated into the area to provide labour. In order to meet the nation's food need quickly, large-scale fields were ploughed and planted using heavy machinery. Massive overexploitation of land occurred as not only the best soils but also soils ill-suited for cultivation (sandy, stony and saline soils) were developed. In the following years, national yields of wheat increased and in this sense the project achieved success, albeit more limited than it was expected. The effects on the steppe environment, however, were adverse. The frequency of wind erosion and dust storms increased dramatically, the runoff in small rivers declined by 40-50% and productivity of pastures and hayfields in the adjacent areas of the Transvolga region decreased by a factor of 2.5-3 (Chibilyov, 1992).

Large-scale production undoubtedly proved damaging and the optimization of structure of arable land is required. Measures aimed at it should involve: introduction of the optimal sizes of arable and irrigated fields; usage of lands best suited for the given agricultural practice; diversification and finding the optimal combination of various types of agricultural activities; and development of agricultural ecosystems which can easily adjust to the natural bioclimatic conditions without exhausting the agricultural potential of the landscape. The single most important measure should be the reduction in arable land and particularly the withdrawal of marginal lands from cultivation. In the past, cultivation of stony, gravely and saline soils and already eroded slopes led to widespread aridisation (.desertification).

Aridisation is particularly an issue in the southern steppe and semi-deserts. It is manifested in the intensive development of erosion, decline in the contents of organic matter, reduction of the above-ground phytomass, and the changing radiation budgets of soils. A distinct indicator of aridisation is the northward advance of the distribution areas of such semi-desert and southern steppe insects and birds as locust and Demoiselle crane and such plants as Festuca and Stipa lessingiana.

Grazing capacity of pastures

Unanimously researchers agree that steppe ecosystems have formed under the influence of grazing livestock. Grazing has always had both beneficial and detrimental effects on pastures. In intensively used pastures, degrading effects of overgrazing occur which, notwithstanding what original types of vegetation association dominated, include a reduction in number of species, mechanical disturbance of soils, and invasion of unproductive species such as ephemerals, emphemeroids and nitrophilous plants (particularly perennial weeds).

The effects of overgrazing on ecosystems have been a focus of research in Russia since the beginning of the twentieth century (Vysotsky, 1915; Pachosky, 1917; Alekhin, 1934; Evseev, 1954; Ivanov, 1958; Gorchakovsky and Ryabinina, 1984; Chibilyov, 1992). However, it is difficult to put these results together and assess the issue for the whole of Northern Eurasia because of the vastness of the area and the different timing of research. Thus in the 1950s, Ivanov (1958) distinguished five stages of pasture degradation in Western Kazakhstan, showing that the productivity of pastures declined from 1.35 kg m"2 (undisturbed pastures) to 0.12 kg m (permanent damage). Similar data were obtained later by Gorchakovsky and Ryabinina (1984) for the Southern Urals. They distinguished four stages of pasture degradation and reported declines in productivity from 1.4 kg m'2 to 0.3-0.2 kg m"2. The detrimental effects of overgrazing are notoriously persistent and it takes a very long time for pastures to recover.

The timing of grazing is particularly important for the steppe ecosystems. Especially damaging is grazing in spring, when soils are still wet after snowmelt. Mechanical pressure of hooves on soil disturbs it, causes compaction and damages plants. Soil crusting, rapid loss of moisture from soil and loss of valuable fodder species follow. Early grazing is widely practised in the southern steppes of the Volga region and southern Urals because of the shortages of forage in winter.

A number of measures have been proposed to use pastures in a more sustainable way and to restore the damaged ones. This includes: evaluation of pasture capacities and compliance with the established norms of grazing; improving winter forage supply and prohibition of early spring grazing; introduction of recovery periods for pastures instead of using them by different livestock; and improving productivity of pastures through mulching, application of fertilizers and artificial sowing of sedges and leguminous plants. The introduction of pasture management was started in the Transvolga region, Southern Siberia and Northern Kazakhstan in the 1980s when livestock numbers peaked. After 1992, a decline in stock occurred. In some regions of Kazakhstan stock numbers decreased by a factor of 2.5-3 and in the Transvolga and southern Urals by a factor of 1.5-1.8. The area of arable land was also reduced, encouraging the formation of fallow soils which are often used for grazing. However adverse the economic effects of agricultural decline were, pastures received a much needed recovery period and the problem of overgrazing has become less pressing.

Irrigation

Although the most intensive development of irrigation occurred in the desert and semi-desert zones, and particularly in Central Asia (see Middleton, Chapter 22), steppe also accommodates a number of large projects. The most unfortunate aspect of irrigation development is that little distinction was made between irrigating desert and steppe soils. Norms of water supply, originally proposed for the arid regions, were introduced ignoring the fact that climate and weather in steppes are different and, unlike in deserts, dry and wet years and spells alternate and so does the moisture contents of soils. Similarly to the infamous irrigation projects of Central Asia, irrigation practises used in the steppe are rudimentary with canals unlined, pipes leaking and return flows not collected properly. The attempt to supply water to chernozems has had a very damaging effect because natural to these soils are a seasonal moisture deficit and a succession of wet and dry years. Instead of improving the quality of chernozems, irrigation has caused a substantial loss of organic matter, a rapid rise of the groundwater table, waterlogging, salnization and the development of erosion. In almost every chernozem region where irrigation was ever practised, there are examples of abandoned fields which originally had a high quality but then became degraded because of irrigation. By 1987, in Russia's steppes alone, 606,000 hectares of arable chernozems had been withdrawn from agricultural use (Egorov, 1989). Particularly damaged were soils in the Rostov and Saratov oblasts. The 10-15 year history of irrigation of chernozems in the Northern Caucasus has led to a two-fold increase of salts in the uppermost metre of the soil (Shipunov, 1989).

Researchers, concerned with the effects of irrigation on chernozems, suggest that irrigation practises in the steppe regions should change and be in future based on the following principles: irrigation should be limited to periods of droughts and norms of water supply should be adjusted to weather conditions: water losses to soil should be reduced by lining canals and furrows; and the groundwater table should be maintained at a depth of 5-6 m (Rozanov et ah, 1983). However, the best solution may be to keep the irrigation of chernozems to a minimum while introducing alternative methods to improve agricultural productivity (Chibilyov, 1992).

Agroforestry

The naturally low woody cover of steppes and the deforestation by humans long ago made scientists and agronomists consider reforestation and agroforestry as measures to improve the climate and water balance in the steppe and forest-steppe. This work was pioneered at the end of the nineteenth century by Vasily Dokuchaev (1891). Already in 1892, working for the State Forestry Department, he established three experimental plots covering 50 km2 each in the Voronezh, Kharkov and Ekaterinoslav provinces with the purpose of developing agromelioration and agroforestry (Dokuchaev, 1895). The major idea was that belts of trees (termed shelterbelts) planted around arable fields improve moisture retention by soils and protect fields from dry winds which are one of the major climatic hazards in the region. Later in the 1920s, following severe droughts in the southern East European plain, the Russian government adopted a series of measures aimed at combating the adverse effects of droughts, emphasizing once again the importance re-forestation and agroforestry. By 1941, about five thousand km of shelterbelts and protective woodlands had been established across the USSR and by 1953 another twenty three thousand km2 had been planted. Now these woodlands have the same ecological, cultural and recreational functions as natural woodlands. They have also proved helpful for the improvement of microclimate, productivity of agricultural ecosystems (through a more favorable climate and by harbouring birds who feed on pests and weed seeds) and regeneration of damaged landscapes. By providing habitats for animals and birds, they improve biological diversity of the steppe and forest-steppe.

Although agroforestry proved extremely successful in the steppe and forest-steppe regions, the completed agroforestry systems are still lacking in the steppes of Russia and even more so in the steppes of Kazakhstan. Even in the Kamennaya steppe in the Voronezh oblast, where one of the Dokuchaev's experimental plots is located, shelterbelts and protective forests around fields occupy less than 1% of all arable land, although the area required is 2.2-2.5%. Only 11% of the shelerbelts needed to prevent gullies from expansion has been established (Shipunov, 1988). Essential to the agroforestry practice is its implementation in full so that it can work as a landscape system in which a balance between various types of woody cover and arable land has been achieved (Chibilyov, 1992).

Restoration of fauna

Before the advent of arable agriculture, steppe and forest-steppe biomes had a rich fauna. According to Mordkovich (1982), the stock number of large (such as marmot and larger) mammals exceeded one billion. There were also a few hundred million large birds such as great bustard. The potential of steppe vertebrates to adapt to the transformation of habitats, caused by humans, varies. Crops provide some species (e.g. ground squirrel, common hamster, rook) with an additional food supply and their populations have increased in marginal lands and pastures. Shelterbelts and protective woodlands provide habitats for other species (elk, roe deer, hawk, woodpecker) who migrate to the steppe from the north. However, agricultural development has had a detrimental effect on most species. Due to the widespread loss of habitat, the distribution areas of many species have diminished, population has been depleted and locally some species (great bustard, tawny eagle) have become extinct.

There are, however, signs that that there is still a potential for the restoration, at least partial, of fauna in the forest-steppe and steppe. Research, conducted in Northern Kazakhstan and the Southern Urals in the 1970s-1980s has shown that across large areas marmots have begun to adapt to the transformed habitats (Dezhkin, 1987; Bibikov, 1989). In the Karaganda oblast of Kazakhstan, the average population density of marmots within the 300 m of an arable field varies between 17 and 21 animals per km2 compared to 25 in the pristine steppe (Kapitonov, 1987) while in the Orenburg oblast its population in close proximity to fields reaches 28-35 (Chibilyov, 1992). Since the early 1980s, the population of tetrax has been increasing in the steppes of Transvolga and the Urals while an increase in the population of the great bustard has occurred in the Transvolga areas of the Saratov oblast (Khrustov et ah, 1997). Forestation and re-forestation, construction of reservoirs and diversification of land-use in comparison with the previous decades reduce pressure on the steppe inhabitants and provide at least some opportunity for the restoration of the steppe and forest-steppe fauna.

Nature reserves and research institutions are also concerned with the restoration or biological diversity. There has been much success in the restoration of the stock of saiga. The population of the Asiatic wild ass, the restoration of which began in 1941 in the Badkhyzsky nature reserve in southern Turkmenistan, has now reached 2000 individuals (Chibilyov, 1990). Attempts are now made to restore the population of tur and to restore European wild horse as a biological species.

THE FUTURE OF THE STEPPE

Steppe and forest-steppe occupy a vast area in Northern Eurasia, extending as an uninterrupted zone from the Carpathian to the Altay mountains. In contrast to most other biomes, steppes and forest-steppes have been transformed by human activities of which agriculture is the most important. Natural steppe and forest-steppe landscapes have been widely replaced by agricultural ecosystems. Not in a single steppe or forest-steppe region of Northern Eurasia do protected areas, accommodating pristine ecosystems, occupy more than 1% of the territory. The degree of transformation varies. On the plains, arable land occupies between 46% and 83% of the territory. The Black Soils region of Central Russia has been transformed most strongly. The steppe and forest-steppe zones are, therefore, represented by three types of landscape: agricultural landscape with artificially created ecosystems (arable land); (2) pastures and hayfields with strongly modified biota; and (3) protected ecosystems which have experienced only minor changes. The nature and functions of these landscapes differ. Although protected areas occupy only a fraction of the territory, their role in the protection of biodiversity and sustaining ecological equilibrium is very important. In many regions, such as the Transvolga and Northern Kazakhstan, there is still a chance of partial restoration and preservation of biological diversity in the areas untouched by humans. The establishment of the Orenburg nature reserve, comprised of fragments of virgin steppe which in the future could serve as 'centres of steppe biodiversity', provides a good example of nature preservation in these biomes (Chibilyov, 1980; 1982; 1993). Another way of partial restoration of steppe ecosystems is the conversion of unproductive arable fields into pastures and hayfields. The share of such lands in the Transvolga and Northern Kazakhstan varies between 18% and 30% (Chibilyov, 1992). The situation is different in the European territory where all opportunities to restore steppes were lost long time ago. Here most important is conservation of small remaining fragments of natural steppes and forest-steppes and regeneration of steppes through the creation of the so-called agricultural steppes, the development of which began in the 1980s in the Ukraine and Stavropol region (Dzyba, 1992).

Preservation of productivity of arable lands is another important issue. However, in order to do so, the approach to agriculture should be revised (Bekarevich and Masyuk, 1983: Rozanov etal, 1983; Chibilyov, 1992; Mordkovich 1997; Blokhin, 1997; Klimentiev, 1997). The new and more sustainable agriculture should rely on techniques which are well suited for natural conditions of the region; reduction of pressure on arable lands and retaining fragments of natural vegetation among arable fields; anti-erosion measures; prevention of the degrading effects of irrigation on chernozems; and further development of protective woodlands. These measures and techniques have been tested by many generations of scientists and practitioners beginning with Vasily Dokuchaev (1892; 1895) and have proved successful. Possibly in the future, the role of steppe and forest-steppe zones as major food providers may be reduced. They could then again become highly productive natural pastures. This, however, requires protection of natural landscapes across the whole biome so that they can serve as refugia and future centers of dissemination of biological diversity.

Table 1 Zonal soils and vegetation in steppe, forest-steppe and semidesert

Table 2 Environmental characteristics and land-use in the steppe biome (sources: Rozov, 1983; Chibilyov, 1992)

Table 3 Environmental characteristics and land-use in the forest-steppe zone (sources: Rozov, 1983; Chibilyov, 1992)

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