Syntaxonomy of zonal dark-coniferous forests of southern taiga of the West Siberian plain and of humid low-mountains of the Altai-Sayan mounain region

The dark-coniferous forests of the West Siberian southern taiga subzone are quite unique. They deter­mine a specific of the Ob’-Irtysh geobotanical field in a sense of V. B. Sochava (1948) together with the West Siberian zonation type (Shumilova, 1979). The main features of zonal southern taiga forests are: dominance of Abies sibirica in a tree layer; species-rich shrub layer; poor ground moss cover; well developed herb layer with a constant presence of nemoral species. We consider the southern taiga forests as hemi­boreal after L. Hдmet-Ahti (1963, 1981). We described the zonal dark-coniferous forests of southern taiga in Milio effusi–Abietetea sibiricae class first proposed by T. I. Zhitlukhina (1988) for the forests in the North-East Altai. Significant increasing of the area studied and existing syntaxa diversity make it necessary to change a diagnostic species group. A new combination of diagnostic species includes Abies sibirica, Padus avium, Lonicera xylosteum, Daphne mezereum, Rubus idaeus, Aconitum septentrionale, Dryopteris dilatata (incl. D. expansa), D. carthusiana, Urtica dioica, Milium effusum, Calamagrostis obtusata, Paris quadrifolia, Allium microdictyon, Stellaria bungeana, Oxalis acetosella, Circaea alpina. Most of Milio effusi–Abietetea sibiricae class communities occur in the West Siberian plain, which is relatively geologicaly young. Due to this fact a flora of southern taiga is mostly allochtonic formed by species migrations fr om the Eastern Europe and the Southern Siberian mountains. Among the diagnostic species the main dominants of tree layer (Abies sibirica) and herb layers (Calamagrostis obtusata and Aconitum septentrionale) have the North Asian distribution. Two shrub species Lonicera xylosteum and Daphne mezereum are European ones and two herbaceous species (Allium microdictyon and Stellaria bungeana) are represented in Europe by vicariant species. All other diagnostic species are Eurasian or Holarctic. Wide distribution of few species, in particular ferns, could be explained by the antiquity of taiga flora (Tolmachev, 1954). Typical habitats of Milio effusi–Abietetea sibiricae forests are the most humid areas with annual precipitation about 500–600 mm on plains and more than 800 mm in mountains. Soils on plains developed under these communities are deeply podzolised type with second humus horizon. In the low-mountains the deeply podzolised soddy-podzolic soils correlate to the area of Milio effusi–Abietetea sibiricae forests distribution. The northern lim it of southern taiga perfectly coincides with the southern border of the largest Pleistocene glaciations. The low mountains of Altai-Sayan system were never glaciated. The thick loess deposits help to survive some nemoral plant species in the isolated refuges. Milio effusi–Abietetea sibiricae class consists of two orders. The order Carici macrourae–Abietetalia sibiri­cae comprises zonal dark-coniferous forests of the West Siberian southern taiga subzone and their successional variants. Diagnostic species are the same as for Carici macrourae–Abietion sibiricae alliance and Aegopodio podagrariae–Abietetum sibiricae association: Gymnocarpium dryopteris, Rubus saxa­tilis, Carex macroura, Aegopodium podagraria, Viola selkirkii, Galium triflorum, Atragene sibirica, Actaea erythrocarpa, Ribes spicata, Stellaria holostea. It contains the alliance Carici macrourae–Abietion sibiricae and three associations. One of these was previously described by N. B. Ermakov but two others are new. Aegopodio podagrariae–Abietetum sibiricae association includes the primary zonal coniferous forests of the West Siberian southern taiga as well as successional stages after some catastrophic events (crown fires, windfall, etc.). Usually it is characterized by closed canopy with Abies sibirica dominance, species-rich shrub layer and well-developed herb layer with high coverage of Carex macroura, Aegopodium podagraria, Stellaria bungeana, Oxalis acetosella and Calamagrostis obtusata. Linnaeo borealis–Abietetum sibiricae association comprises the zonal coniferous forests grown in the northern part of southern taiga subzone. Its diagnostic species: Linnaea borealis, Trientalis europaea, Luzula pilosa, Orthilia secunda, Lycopodium annotinum, Vaccinium vitis-idaea are common for the Vaccinio-Piceetea class communities. In contrast with previous association Linnaeo borealis–Abietetum sibiricae communities are characterized by multi-dominant tree layer with slight predominance of Abies sibirica; shrub layer is sparse and not so species-rich, in herb layer the main dominants are Carex macroura, Oxalis acetosella, Calamagrostis obtusata, Gymnocarpium dryopteris and sometimes big ferns. Moss cover is about 20 to 40% of soil surface. The order Abietetalia sibiricae consists of low-mountain chernevaya taiga and dark-coniferous mountain forests of the Altai-Sayan humid sectors. A set of diagnostic species includes Ribes atropurpureum, Saussurea latifolia, Geranium albi­flo­­rom (incl. G. krylovii), Euphorbia lutescens, Myoso­tis krylovii, Viola uniflora, Dryopteris filix-mas, Heracleum dissectum, Trollius asiaticus, Anemonoides altaica, Corydalis bracteata, Erythronium sibiricum. The most of diagnostic species are north-Asian or south-Siberian ones. Many of them are mountainous restricted to the Altai-Sayan mountain system. This order includes one alliance Milio effusi–Abietion sibiricae previously described by T. I. Zhitlukhina and N. B. Ermakov. Seven associations belonging to this alliance were described and characterized by N. B. Ermakov (2003). When thinking about further development of the class syntaxonomy we expect the diversity increasing by serial communities of mixed and small-leaved forests and swampy forests on a plain. We do not discuss western and eastern class limits now. No doubt that distribution area of the new class is wider than the West Siberia but to describe its limits and an interaction with neighboring classes some additional materials are needed.