Saturday, 15 July 2006

Soils of Taiga and Their Evolution in the Course of Forest Successions.

Lev O. Karpachevskiy, Moscow State Univ, Faculty of Soil Science, Leninskie Dory, home 1, stroenie 12, Moscow, 119992, Russia, Mikhael L. Karpachevskiy, Moscow State Univ, Leninskie Gory, Moscow, 119992, Russia, and Tatiana A. Zubkova, Moscow State Univ, Facultty of Soil Science, Leninskie Gory, h.1, stroenie 12, Moscow, 119992, Russia.

Most of the boreal zone in Russia is occupied by larch forests, followed by spruce, pine, fir and secondary birch and aspen forests. Forests of alder, bird cherry, willows and poplars are typical found along water streams. It should be noted that the proportion of secondary forests dramatically increased as a result of massive industrial logging during the 1930-1990s. The main soil types in taiga (or boreal forests) are represented by podzols on sandy deposits (under pine stands), podzolic soils (Albeluvisols) and their more southern variants with a more profound sod horizon on loamy deposits, brown forest soils (Cambisols) in the Ural, Sikhote-Alin and Transbaikal mountains and analogs of these soils on sandy and loamy sandy deposits (under complex pine stands). Variants of peaty podzolic gleyed soils (Histosols) prevail in northern taiga. They can be also found to the south as small patches. Bogs with a peat layer up to 10-12-m thick are also a widespread type of ecosystems within the boreal zone. Such wetlands may form vast homogenous areas (like bogs Staroselie and Katin Mokh in Tver Oblast). Specific analogs of brown forest soils (named taiga-soddy soils by O.V. Makeev) characterized by light brown and pale colors but lacking textural differentiation develop on eluvium of basic rocks in Eastern Siberia. Variants of brown forest soils with the red-brown B horizon occur on the outcrops of red-colored Permian deposits in Cisurals. In northern taiga and mountains podburs (soils enriched with organic matter in the upper layer but lacking clear vertical differentiation) can be found. Various Umbrisols, Histosols and Gleysols occur along the water streams. The latter type is especially widespread in the taiga. Northern and middle taiga in Siberia is dominated by Cryosols. All forest soils are characterized by anisotropy: regular changes in morphological, physical and chemical properties from the soil surface downwards as well as in space (a specific tessera forms around individual edifier trees). After logging, forest fires and catastrophic damage by pests (e.g. massive attack of Siberian silkmoth, which destroyed vast areas in Siberian taiga in the 1970-1980s) soil characteristics change. Thus, specific organic sod horizon and well manifested A horizon develop. Some wet soils on which most of trees was removed or died are subject to paludification. Such soils evolve into peaty podzolic gleyed soils (Histosols, Gleysols). As trees regenerate on felled and other treeless areas, soddy (Umbrisols) and peaty soils (Gleysols) evolve into zonal podzolic and brown soils. Within the taiga significant areas are occupied by Regosols and Rankers. The soil cover of the Kamchatka Peninsula is almost exclusively represented by Andosols. It should be noted that most of Rankers and other soils with the thick humus horizon are formed due to continuous accumulation of fine soil matter on the soil surface. This is typical for many brown forest soils (Cambisols), soddy soils (Umbrisols), volcanic ash soils (Andosols) and alluvial soils (Fluviosols). Within one forest type soil evolution can be driven by windthrow of individual trees, which lead to formation of mound-and-pit topography. In depression, Gleysols (peaty podzolic soils) develop, which gradually evolve into Albeluvisol (soddy podzolic soils). On the mound, Umbrisol (soddy soil is formed), which later evolves into soddy-podzolic soils (Albeluvisol).

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