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Gracheva R., Targulian V. Institute of Geography of RAS, Staromonetny 29, 109017 Moscow, Russia Soil is a main life-supporting factor in mountain regions. At the same time the soil is the most fragile and vulnerable component of the mountain nature. The main reasons of the mountain soil vulnerability are: a) the shallow total thickness of the mountain regolith usually underlined by consolidated rocks; b) shallow and stony soils limited by regolith depth; c) high rates of the natural denudation and human-induced erosion; c) the general discordance between the relative low rates of fine earth substances generation by weathering and high rates of these substances loss by denudation, partucularly by anthropogenic erosion. It means that any loss of the fine earth from the mountain soils and regoliths are practically unrenewable and irreversible within the human time-scale. Accordingly, in mountain regions the fine earth properly and the whole regolith mantle including the soil cover are the strategic unrenewable natural resource for human habitat, agriculture, forestry, etc. It is the essential peculiarity of mountain soils as distinct from lowland ones, which are usually developed on thick loose deposits and, as a result, have an unrestricted resource of fine-earth mineral materials. The perception of the fine-earth finiteness and unrenewability in the mountains means that not only soils should be an object of conservation, but all kinds of regolith mantle covering mountain watersheds and slopes. Just whole regolith is the main object of human impact and "victim" of many natural catastrophes (slides, avalanches, mud flows). The irreversible loss of the whole loose mantle seriously damaged or even ruined the social and economical life in many mountain regions (Caucasus, Central Asia, Mediterranean, India, Ethiopia, etc.). The natural regeneration of fine earth in mountains depends on different factors such as rocks properties, climate, topography, but in the most cases needs centuries and thousands years, which is too much for the human expectations. The importation or making of fine-earth for mountain soils are extremely expensive and not available for mountain communities even in developed countries. So, the sustainable development of mountain regions tightly related to the existence and conditions of their soil and whole regolith mantle, primarily to the total thickness and fine earth content. Soil variability in mountain regions often is a result of successive erosion loss of surface loose matter and involving of deep horizons of regolith mantle into soil formation. The soil diversity within erosion sequence depends on the thickness and properties of the soils and subsoils which are subjected to erosion, and on the correlation between the rates of soil loss and soil formation. The most wide erosion-dependent spectrum of soils is formed in humid tropics and subtropics where the different horizons of the thick soil and saprolite profiles are exposed as a result of long-term natural and human induced erosion. The new soils derived from material of various exposed horizons inherit properties of substrata and differ in acidity, texture, mineralogical composition, the reserve of nutrient elements, and other ecologically important features. On eroded hills and terraces of the east coast of the Black Sea the following spatial-erosional soil sequence is formed: Stagnic Acrisols and Haplic Nitisols, derived from red clayey soft saprolite; Eutric Cambisols, derived from loamy brown saprolite, and Lithic Leptosols as a final component, derived from coarse brown saprolite or desintegrated rocks. Generally, erosion sequence includes soil profiles from strongly acid clayey kaolinite to weakly acid or neutral polymineral coarse textured, and this fact determines the ways of agricultural activity in the region. Distribution of managed ecosystems correlates with soil pattern very closely. As soil erosion advances, acid-tolerant plants such as tea are changed by lime-loving and xerophyte crops on young soils, and the final ecosystems are pine or shrub stands or badlands. The main goals of soil science related to the problem of sustainable mountain development are:
- to define the rates of fine earth generation processes (weathering, pedogenesis, sedimentation) in different environments; - to explain to mountain stakeholders the extremely important life-supporting role of the loose soil and regolith mantle for the long-term sustainable development. |