| Summary: | The disturbances to soil horizonation and to organic matter pools caused by harvesting were assessed in a Middle Taiga zone. Soils were sampled before (pristine forest) and 5 years after clear-cutting in a Russian boreal forest near the village of Ust’Kulom (Komi Republic). After clear-cut, the logging residues were left in place, and forest allowed to naturally regenerate. At both sites, soils were bisequal: they showed a sequence of O horizons followed by E and spodic ones, and eluvial horizons depleted in clays overlying argic ones. At the clear-cut site the organic layers thickness was higher and an E/A horizon was also present, above the E one. The soils were characterised for the principal chemical and physical properties. Fractionation of humic substances was carried out on the horizons forming the Podzol sequum: after NaOH-extraction, humic (HA) and fulvic acids (FA) were separated by HCl acidification, purified and freeze-dried. Humic fractions were investigated for their chemical composition by elemental analysis, E4/E6 ratio and FT-IR spectroscopy. The results showed a translocation of organic matter, as expected, with an accumulation of carbon in the spodic horizons. At the clear-cut site, the mineral horizons showed generally lower carbon contents than in the pristine forest, although the organic layers were enriched in C. The C to N ratios were higher than those found at the pristine site, while the humification ratio was lower. In both soils, an accumulation of oxalate extractable-Fe (Feo) and Al (Alo) was visible in the mineral horizons enriched in organic carbon, and their trend with depth was related to the variations in the FA/HA ratio. The spodic index (Alo+0.5Feo), used as a taxonomic evidence for spodic horizons, pointed towards a more intense translocation of metallorganic complexes in the clear-cut site. In the pristine forest the Bhs was too shallow to allow this soil to be identified as a Podzol. According to the WRB, the soils were an Albeluvisol (pristine forest) and a Podzol ...
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