Spatial organization of mountain landscapes
Introduction. Study of spatial landscape hierarchic organization is one of the main trends in the landscape science. Many interesting publications, based on some new approaches, are devoted to this problem (Armand, 1988; Kolomytz, 1998; Puzachenko, 1997; Solntsev, 1997 and etc.), but the majority of them deal with the organization of plain regions. Landscape structure of mountains and it dynamics were studied by K.I. Gerenchuk (1968), N.A. Gvozdetskiy (1972), A.A. Makunina (1974), G.P. Miller (1974), N.L. Berutchashvili (1995) and other scientists. Therefore only few investigators used the approach of nuclear and vector geosystems, widely spread in the mountains.
The main goal of this research is to reveal the regularities of a spatial landscape organization of mountain regions and factors of it formation on different hierarchic levels. The investigation based on the analysis of multiscale landscape maps on the Gorny Altay, the northern part of the Internal Asia and the Caucasus, compiled by the authors during fieldwork as well as decoding of space images.
Two interrelated approaches were used while study: traditional structural-genetic and functional-dynamic. They indicate the main types of mountain landscape differentiation. In the first approach we focus our research on geosystems of different hierarchic levels, the spatial composition of which characterize the horizontal (plane) landscape structure of the territory and mainly the discreteness of the geographical space.
The second one is based upon the study of landscapes as a functionally holistic systems joint by the lateral flows and the interconnections between them.
Spatial (plane) landscape organization. Two levels of the spatial landscape organization - regional and local, characterized by their own features of formation and functioning, are well defined practically in all mountain regions. Altitudinal zonality, characterized by composition of altitude belts with landscapes of different types and subtypes, is the main regularity of spatial organization on the regional level of differentiation in the mountains. The basic factors, determining the landscape structure on this level, are the position, tectonics, topography and climate. Different spectra of landscape altitudinal zonality are formed in the mountain physical-geographical countries and provinces.
At the local level the lithogenic basis and modern exogenic processes, are the most important factors of interzonal differentiation, determining the structural complexity, diversity, heterogeneity and metachronics of mountain landscapes (Avessalomova et all., 2001).
All factors of physical-geographical differentiation are classified into universal, which are common for different altitude belts and specific ones, localized in the certain belt. Tectonic factor, one of the main universal factors, forms the landscape frame, consisting of local geological structures and system of tectonic faults. It causes the common landscape composition, the orienting position of landscape contours and erosion forms with activity of exogenic processors and mechanic migration of material, the state and intensity of which change in different altitude belts. The glaciations and snow processors in the glacial-nival belt, intensive erosion in the forest belt and arid denudation in the steppe and semi desert zones, karst in the regions with carbon rocks and other exogenic processors can be mentioned among specific factors.
The variety of modern nature conditions, the complexities of mountain history in the Quaternary period, including climatic fluctuations determined the polygenetic and metachronic of landscape structure. The abundance of geosystems of different age indicates widespread of glaciations, activity of exogenic processors and lateral migration. The contrast of landscape boundaries increases due to the changes of humidity, relief, lithologic compound of rocks, becoming more notable in the places with joint action of factors, for example of exposition and steepness and so on.
Nuclear organization of landscapes. The approach, using the concept of the nuclear geosystems (Reteyum, 1988), is long-rang for the study of mountain landscape structure. The differentiation of geosystems on nucleus and membrane (geographical fields), where the impulse of nucleus-body markedly decreases in the direction to it periphery, is typical at different hierarchic levels of spatial landscape organization. The landscape nucleus has climatic and geoflow-forming, macrotranseluvial geochemical, phytocenetic and other functions. It is crucial that their significance for landscape formation vary according to the regional features of the mountain areas - the specific mesonuclei, characterized by more homogeneous landscape structure. The configuration of the nuclei as well as of the nuclear geosystems may be rather diverse - round (Elbrus, Kluchevskay Sopka), ellipsoid, asymmetric (Caucasus, Ural) and so on. The nucleus center is usually the highest part of the mountains with rotary motion of the lateral flows. But it may be also the large sized lowered tectonic block with lake or intermountain basin (Baikal). In this case the landscape structure has inversion character.
The structure of landscape nucleus of high hierarchic level consists of the nuclei of low levels and connection between them determine the common features of the region. The nuclei of regional level (macro- and meso-) have rather various landscape structures - relatively simple, complex, but their functioning is predetermined by common trend of different processes as redistribution of the heat and moisture, lateral migration, typical for the meganucleus at whole. The pulsated character of landscape forming processes is common for these geosystems. In palaeogeographical aspect this feature was revealed in the Quaternary glacier fluctuations, nowadays in the changes of warm and cold seasons, years and so on.
Formation of mountain nuclear geosystems are more typical for the contacts of geo- and morphostructures of high levels - the Northern Sibiria, the Ural, the Caucasus, of low levels - to the Kluchevskay Sopka, the Elbrus, the Patomskoe nagorie and so on. Term "nuclear geosystems" in this case is closed to the definition of landscape "consenters" by V.S. Mikheev (1987), but differs due to the more concrete landscape structure and interconnections in nuclear geosystems.
The mountains of the Northern Internal Asia and the Caucasus can be chosen as good objects for study of the main features of nuclear organization on different levels (Table 1).
Meganuclear geosystem of the Altae-Khangae-Sayan region is a specific landscape nucleus, characterized by polystructure and asymmetric configuration with south of Western Siberia and the center of Mongolia as geographical fields of it influence. The functions of this nucleus are diverse with flow forming as a more vital. The biggest Siberian rivers - the Ob, the Yenisei and their tributaries begin in this region -a world watershed of the Artic Ocean and the Internal Central Asia. Formation of their run-off is determined by nature conditions of these mountains, mainly of regime of solid and liquid precipitation, glaciations and so on.
Nuclear geosystems of the regional level
The polystructure of landscape nucleus of this region is closely connected with it continuum position in several zones - the south of taiga, steppe, subdesert and the northern part of the desert as well as with diversity of relief (from intermountain depressions to low-and high mountains with alpine-meadow and glacial-nival landscapes), with northwestern orienting of the majority of ridges, with barrier climatic effect and extreme nature conditions. The geostructures of high level, reflected in various morphostructures of the territory, determined the formation of nucleus landscape frame. The Quaternary glacier fluctuations with more notable tracks in the center of the landscape nucleus caused changes of relief as well as of the whole landscape and formed the contour of the lithogenic basis of some nuclei of the low levels. The inner boundaries of this landscape macronucleus are mainly determined by regional tectonic faults as Altaiskiy, Sayanskiy and others. Some mesonuclei within macronuclear geosystems have also distinct boundaries of orotectonic character, but some of them can be marked often only by specific features of landscape structure, which formation have been caused by the joint interconnection of factors with climate as predominant (Western Altay and etc). These nuclear geosystems formed in the "cyclonic" climatic provinces with west air mass and high humidity.
The extreme nature conditions in the center of Asia as aridity and cryogenesis, which are often incompatible, also affected the spatial organization of the nuclear of this region. The cryogenic processors and phenomena decrease from the center to the periphery in north and south direction, where they are marked out only on the local level of differentiation. The steppe geosystems, as indicators of aridity, are widely spread in the south part of the nucleus, distributing local in the north boreal landscapes as facies - the complexes of the lower level. The arid geosystems are also typical for the meridian orienting valleys - specific vector systems binding the nucleus in with it periphery.
Altay is the typical landscape macronucleus of regional level with the most complex structure among the regions of the Northern Internal Asia. It consists of some interconnecting mesonuclei. The landscape structure of Central Altay (Katunsko-Chuiskiy mesonucleus) as one of them is very polystructure. The high altitude ridges (to 4506 m), dissected by valleys, the prevalence of sublatitudinal orienting ranges with exposure differences caused the diversity of landscapes - from steppe to glacial-nival. The specific concentrate zonality of ellipsoid type is typical to the spatial landscape organization of this nucleus. The position of landscapes to the certain altitude belts is affected by the activity of different flows, mainly of gravity processes, snow avalanches and other, decreasing the height of landscape zonal boundaries (for example of forest type) and making landscape structure more complex due to the appearance of "lithogenetic" complexes.
The predominance of the dark coniferous forests in the middle mountains and subtaiga asp-abies height grass low mountains, forming in the humid conditions is typical for another nucleus - the Telezkoe lake region. The grass relicts of Palaeogene-Neogene flora retained in this nucleus, indicating the absence or small glaciations in Pleistocene and it "warm" variant. Landscape structure of the membrane of this nucleus is also very specific. The lateral and substantial-energy flows caused the widespread of taiga and subtaiga landscapes on the piedmont plain in the north and the formation of intrazonal geosystems in the forest-steppe ecotone. The landscape membrane of this nuclear geosystem has limited area in the south and it landscape-forming role reveals only on the northern slopes by appearance of boreal geosystems.
The interconnection of nuclei is determined by the geoflows of different kinds - water, aerial, gravitation and so on. Landscape structure of the ecotone type form in the zone of their interconnection. The landscape structure of the Northern Altay is a good example of this type with prevalence of forest-steppe of exposure character. The steppe exists under the impact of plain landscapes and formation of their loess-like soils is closely connected with the opposite influence of landscape membrane of the Altai at whole. The origin of taiga geosystems is caused by the direct influence of nucleus surroundings.
While South-East Altay is the part of the Mongolian nuclear with typical subdesert depressions and unique tundra-steppes in the high mountains, the Eastern Altai is the zone of interrelation of surrounding nuclei and their geographical fields (membranes) with a great role of palaegeographical conditions - numerous glaciations with centers in Katunsko-Chuiskiy, Mongolian and Mongon-Taiginskiy nuclear geosystems. The planation surfaces with glacial deposits under larch forests and ernik-tundra are the most typical complexes here.
Thus Altai as a macronuclear geosystem with complex landscape structure consists of interacting nuclei of low hierarchic level with substance-energy lateral flows between them.
The mountains with active nuclear geosystems with contrast fields round the nucleus body are distinguished by original structure. Volcano Elbrus in the Great Caucasus is an example of this mesonuclear geosystem of regional level. It represents a nuclear with centrifuge motion of substance in it center with pulse functioning as a result of it periodical eruptions, beginning from the upper Pliocene when Elbrus acted firstly. It directly impacted surroundings by lava flows and cinder as well as intensive lahars forming during eruptions. The joint action of different factors aggravated the endogenic substance-energy potential of nucleus, intensifying its impact. In time the landscape structure of Elbrus nucleus and its membrane became complex due to the formation of several volcanic cones and plateaus with diversity of inner structure. Volcano Elbrus is in a rest-stage nowadays. The radial type of landscape pattern is typical for Elbrus nucleus as a result of spreading of glaciers and fluvioglacial flows from the common center. The specific star-shaped type of glaciations is typical for this region. Some independent vector geosystems, separated in space, formed in its periphery. The increasing of climatic and landscape aridity in the Baksan valley with pine-tree forests on the northern slopes and steppes on the southern slopes is another originality of Elbrus surroundings due to the great height of this volcanic massif.
The glacial-nival geosystems can be also regarded as landscape nuclei. The decreasing of zonal boundaries, the reductions of zonal landscapes (for example, alpine and subalpine-meadows) are marked out to their surroundings. These fields (membranes) with asymmetric configuration are well defined near valley glaciers. The avalanche snow patterns are another nuclei of nuclear geosystems of local level.
Vector geosystems. The cascade and catenary's geosystems, widely spread in the mountain regions, are another original feature of their spatial landscape organization. These geosystems are formed due to the high altitude gradients, intensive gravigenic processors, and the prevalence of lateral links on the different levels of differentiation. Cascade system consists of a serial of geosystems, changing each other from watershed to the local depression, and join by lateral migration flows, where individual complexes are the components of the whole system (Glazovskaya, 1988). In the cascade geosystem the substance-energy flow on leaving one complex becomes the entrance flow to another one, located on the lower altitude.
Three main zones with different inner spatial organization can be defined in the cascade geosystem - zone of formation, zone of transit and zone of substance and energy accumulation. Usually they belong to the different altitude belts that cause the increasing of landscape complexity.
The formation of biota within cascade geosystem is determined by radial links, causing the originality of landscapes. The lateral flows can reduce the radial links favoring the formation of landscape ecotones of different hierarchic levels.
Two types of cascade systems are often can be revealed in the mountain regions. The first one is connected with area flows such as diluvia, nival, area avalanches and so on. The cascade systems joint by linear flows such as debris-flows, alluvial, erosion and others belong to the second type.
There is no classification of vector systems nowadays. But we may classified them according to the level of spatial organization as well as for their genesis, dynamics, position in different altitude belts and so on.
Landscape patterns. Varieties of landscape-forming factors and their local composition in the geospace determine the mosaic of spatial structure of mountain geosystems, which reflect in different landscape patterns. Several types of such patterns can be marked out usually in the mountain regions. The parallel-polygonal pattern is typical for ridges dissected by cross-sectional and linear faults that determine the frame lines of landscapes with transit zones of water and gravigenic flows. Fan-shaped or fan-blade patterns indicate the zones of flow accumulation with cones of different origin (debris flow,
snow avalanche and other). Semi concentric texture is usually typical to area with avalanches of the same magnitudes and where snow-patch represents the nucleus-body of very specific local nuclear geosystem. Banded pattern is marked out in the regions with concavo-convex slopes of ridges. This pattern is well defined on the dissected slopes with exposure differs particularly in the arid climate. Spotty pattern is typical for regions with activity of area exogenic processors, such as landslides and so on. The alternation of steep and gentle slopes, formed by rocks with different stability for denudation, determines the parallel-striped pattern of landscape structure. Arched pattern usually indicates the high mountain geosystems with modern and ancient glaciations. Specific radial structure is typical for mesonuclears of volcanic cones as well as for farewell rocks of high planation surfaces with dissected slopes. Dendritic pattern indicates territories dissected by water flows and erosion forms.
The combination of different landscape patterns are usually typical for mountain regions due to the tectonic activities, high climatic gradients, intensive exogenic processors, prevalence of lateral flows.
Conclutions. Two levels of the spatial landscape organization - regional and local, characterized by their own features of formation and functioning, are well defined in study regions. Landscape structure on the local level is particularly polystructure and metachronic.
The study of the nuclear geosystems in the mountains of the Southern Siberia and the Caucasus makes it possible to reveal some common features of their structure: 1/ the polystructure of the landscape nucleus, determined by the character of their evolution and pulsating in time; 2/ the hierarchy of the nuclear geosystems, the modification of their complexity on different levels (regional and local) and the divestiture nucleus of the different levels (mega-, macro- and so on); 3/ interconnection between nucleus and their connection with the surroundings by the matter and energy flows (vector geosystems).
In comparison with plains mountain regions are distinguished by high activity of unidirectional lateral substance-energy flows and widespread of vector geosystems. At the local level it promotes the increase in the complexity and the continuous modification of the morphologic landscape structure within different altitude belts.
Further research proposes the nuclear systems classification, the determination of their diagnostic features, the analysis of the impact of landscape-geographical fields and the parameterization of their substance and energy flows (cascade, catenary's and so on).
This work was partially supported by Russian Fund for Basic Research (grant 03-05-65024).
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