Saturday, 15 July 2006

Common Features of the Soils of Forest Biogeocenoses.

Vladimir F. Val'Kov, Rostov State Univ, B. Sadovaya Str., 105, Rostov-on-Don, 344006, Russia

Under modern conditions of biosphere functioning, forests represent such indispensable global phenomena as cumulation of living substance and of essential chemical elements, as well as preservation of the carbon-oxygen balance established through centuries. The forest and herbaceous flora in the diversity of its life forms are the basic types of the Earth biogeocenoses. The zonal nature of forest associations varies from boreal taiga forests to tropical rain forests. Given the vast diversity of bio-ecologic extensional authenticity, all forests are the same in their soil-genetic essence. At vegetation period temperatures not lower than 50F (10 Celsius), the humid climate of the forest causes constant soils irrigation. Thus, substances which are water soluble should be washed out of soil. However nutritive materials are hardly ever carried away. Forest phitocenoses have formed out as eluvial-proof vegetation type. The essence of this adaptation lies in the mechanism of the forest cumulating and retaining the necessary stock of organogenic elements not in the soil itself, but in the biomass, which is much safer. The biological circulation of elements in a forest association is close to direct exchange of elements between living organisms and their litter. Elements in a forest association migrate by means of solutions of various substances ascending to the leafage and fixing in the biomass of the trees. The biological circulation of elements in a forest association features the following: the litter forming the forest floor is the main source of plants nutrition, the biomass is the major stock of biophilic elements. The concentration of the elements for mineral nutrition in the biogenic substance is the most important characteristic of forest biogeocenoses. The major ecologic function of soil in the forest biogeocenoses is to provide optimal conditions for unhindered growth of tree rootages with their high absorbing capacity. The term “fertility” applied to natural conditions loses its agronomic sense as the ability to satisfy the needs of vegetation is characteristic not only of the soil but of the biological association itself. At the same time forest soils being the habitat of tree rootages may be estimated from the ecological point of view as high fertility soils despite their agricultural inutility. This proves the fertility paradox: there is no soil absolutely fertile, there are only soils fertile for this or that biocenosis. Almost all forest soils, especially Podzols and Ferrasols, strongly lack bioorganic elements, their layers are almost non-humus, but despite being well-irrigated, at the same time they are the substratum for extraproductive biogeocenoses. The forest soil sideview is constituted by two functional layers. The surface layer of the forest floor represents maximum concentration of different processes varying in their biological essence. This layer is constantly renewed and provides the stability of the biological circulation. The underlying mass possessing a certain geographic specificity of genetic layers is not capable of retaining the chemical elements, but these layers are optimal environment for developing vast rootages able to capture from this forest floor everything that is biologically vital

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