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The communities of middle taiga spruce forests (ass. Linnaeo borealis–Piceetum abietis dryopteridetosum var. typica) and secondary communities formed after winter clearcuttings are described (Fig. 1) and classified according Braun-Blanquet (1964) approach using 81 relevés. Ellenberg ecological values (Ellenberg et al., 1991) were used to assess lighting (L), soil moisture (F), acidity (R) and nitrogen (N). The ordination was carried out using the NMS method. Both primary forest and secondary communities are classified as the alliance Piceion excelsae Pawłowskiet al. 1928 within the order Piceetalia excelsae Pawłowski et al. 1928 in the class Vaccinio–Piceetea Br.-Bl. in Br.-Bl.et al. 1939. We described 2 associations (incl.  1 new), 3 subassociations (2 new), 2 varieties (1 new), 2 subvarieties, and 2 communities. Ass. Aulacomnio palustris–Calamagrostietum purpureae ass. nov. hoc loco (Table 2). Nomenclature type (holotypus hoc loco): relevé 16 (field № 26p/20), Komi Republic, Ust-Kulom district, two-year cutting place, swath (61.84083° N 54.33778° E, 16.07.2020, author I. A. Likhanova. Diagnostic species (DS): Aulacomnium palustre, Calamagrostis purpurea, Carex globularis, Chamaenerion angustifolium, Polytrichum commune, Sphagnum angustifolium. The association includes «young» (succession stage 1(2)-17(18) years after cutting) secondary communities, formed at the swaths and skidding trails. The absence of tree stand results in the increased lighting and soil moisture, which explains an invasion of heliophile and water-resistant species of vascular plants and mosses. After cutting, DS of the primary association and subassociation almost disappear, but those of class and order remain. Species number — 23–54, average — 38. There are 2 subassociations within aasociation. Subass. A. p.–C. p. typicum subass. nov. hoc loco (Table 2 relevés 1–16, Fig. 3). Nomenclature type (holotypus hoc loco): relevé 16 (field № 26p/20), Komi Republic, Ust-Kulom district, two-year cutting of spruce herb-bilberry-green moss forest at the swath (61.84083° N 54.33778° E , 16.07.2020, author I. A. Likhanova. No own DS. The subassociation includes communities at the swath and skidding trails of 1(2)-year cutting place with poor species richness in comparison with primary forests. Number of species 20–27, average – 24. Subass. A. p.–C. p. avenelletosum flexuosae subass. nov. hoc loco (Table 2, relevés 17–27, Fig. 4). Nomenclature type (holotypus hoc loco), relevé 25 (field № 13-УК), Komi Republic, Ust-Kulom district, 17-year cutting place, swath (61.99389° N, 54.14778° E , 17.09.2019, author I. A. Likhanova. DS: Avenella flexuosa, Gymnocarpium dryopteris, Rubus arcticus.The subassociation includes communities of swaths and skidding trails at 17(18)-year cutting place enriched by heliophile and water-resistant species. The forming forest environment is the reason of high abundance of forest species and emergence of several diagnostic species of primary association and subassociation. The cutting remains are overgrown by epigeous mosses and lichens. Species number — 24–45, average — 33. Community Carex brunnescens (Table 3, relevés 1–12, Fig. 5). DS: Carex brunnescens (dominant), C. canescens, Ceratodon purpureus, Dicranella cerviculata (dominant). Syntaxon includes communities at the main skidding trail at 1(2)-year cutting place. Despite high abundance of diagnostic species of the ass. Aulacomnio palustris–Calamagrostietum purpureae, we can’t include the relevés into the association due to high diversity of early succession species and low abundance of DS of both the class Vaccinio–Piceetea sylvestris and the order Piceetalia excelsae. There are numerous undergrowth of Betula pubescens (18 thousand ind./ha). Herb-dwarf shrub and moss layers are formed by pioneer, heliophile and water-resistant species. Forest dwarf shrubs, herbs and mosses occur on the litter remnants. Species number — 20–34, average — 27. Community Salix caprea. (Table 3, relevés 13–22, Fig. 6). DS: Agrostis gigantea, A. tenuis, Carex rhynchophysa, Deschampsia cespitosa, Epilobium palustre, Juncus filiformis, Populus tremula, Salix caprea (dominant), S. myrsinifolia, S. phylicifolia, Sphagnum russowii. The syntaxon includes communities at the main skidding trail of 17(18)-year cutting place. The presence of DS of ass. Aulacomnio palustris–Calamagrostietum purpureae and subass. A. p.–C. p. avenelletosum flexuosae as well as the prevalence of water resistant and early succession species and low abundance of DS of class Vaccinio–Piceetea sylvestris and order Piceetalia excelsae are character. Tree stand is formed by young trees of Betula pubescens (mean density is 21 thousand ind./ha). Shrub layer is formed by wiilows. Herb-dwarf shrub layer is dominated by species, preferring water logging, and species of disturbed habitats. Species number — 36–45, average — 40. Subass. Linnaeo borealis–Piceetum abietis dryopteridetosum var. Betula pubescens (Table 1, relevés 13–22). DS: Betula pubescens (dominant), Milium effusum, Rhytidiadelphus triquetrus. The variant includes communities at 48(49)-year cutting place. The tree lyer height and crown density are comparable to those of the indigenous spruce forest, however, the proportion of birch is higher. Vascular plant DS of ass. Linnaeo borealis–Piceetum abietis and subass. dryopteridetosum are registered, but the abundance of moss DS is low. Many forest species become abundant in the herb-dwarf shrub layer. Moss layer is inhibited by leaf litter. Species number — 29–45, average — 36. There are 2 subvarieties: typica (communities at the swath and skidding trails) and Calamagrostis purpurea (main skidding trail). The scheme of vegetation succession after clearcuttings of spruce small herb-bilberry-green moss forests (Linnaeo borealis–Piceetum abietis dryopteridetosum var. typica) (Fig. 10) is made on the results of NMS-ordination (Fig. 9) and the data on the restoration period and preferences of syntaxa to the certain technological elements of the cutting place. The following succession series are described: at the swaths and skidding trails — Aulacomnio palustris–Calamagrostietum purpureae typicum → A. p.–C. p. avenelletosum flexuosae → Linnaeo borealis–Piceetum abietis dryopteridetosum var. Betula pubescens subvar. typica → L. b.–P. a. dryopteridetosum var. typica; at the skidding trails – community Carex brunnescens →community Salix caprea → Linnaeo borealis–Piceetum abietis dryopteridetosum var. Betula pubescens subvar. Calamagrostis purpurea → L. b.–P. a. dryopteridetosum var. typica. In communities of different ages at swaths and skidding trails, the species richness of vascular plants (16–18 species/100 m2) and mosses (8–10 species/100 m2) is lower compare to the primary spruce forest (19 and 14 species/100 m2 respectively). The species richness of vascular plants at 17-year and 48-year communities of the main skidding trails (27 species/100 m2) is higher than in the primary forest due to the invasion of pioneer, meadow and mire species; that of mosses is lower (8–12 species/100 m2). Thus, the cutting has a negative impact on species diversity, which is expressed in forest species loss. The floristic composition of the disturbed forest community is not restored even fifty years after anthropogenic impact.

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Управляемое восстановление лесных экосистем на песчаных техногенных субстратах крайнесеверной тайги Европейского северо-востока России Работа выполнена в рамках темы государственного задания ИБ Коми НЦ УрО РАН «Выявление общих закономерностей формирования и функционирования торфяных почв на территории Арктического и Субарктического секторов Европейского северо-востока России» (АААА-А17-117122290011-5)

The article considers the role of hydromorphism in the soil formation processes on ancient alluvial sandy deposits at the primary succession period. Soil organic matter was given special attention. The studies were carried out in the European north-east of Russia (the Komi Republic) in the middle taiga subzone in the territory of a building-sand quarry (61°57′35″ N, 50°36′22″ E) and background sites near the quarry. The authors analyzed the morphological structure of soil profiles, and the principal physical-chemical properties of mature and young soils forming under pine forests. Formation of forest litter and humus-accumulative horizons, as well as soil organic matter accumulation were thoroughly studied. Already in the fourth–fifth succession decades, the soils in a series of increasing hydromorphism actively demonstrated regularities that sre normally characteristic of background soils, for example, increase in acidity, silt fraction, carbon and nitrogen reserves. Against moisture deficiency, the accumulation rate of organic carbon became slow and amounted to 0.07–0.11 t ha−1 year−1. The excessive soil moisture content increased the rate up to 0.38–0.58 t ha−1 year−1 due to the conservation of plant material in the form of peat. The upper 50-cm profile layer contained Corg 2–4 times less than that of background soils. The major soil-forming processes are litter formation and podzolization in drained conditions, litter formation in conditions of high moisture, and peat formation and gleization against excessive moisture.