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Biomes and Regions of Northern Eurasia

Boreal Forests

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Western Siberian Taiga

In Western Siberia, the taiga zone is marked by a widespread occurrence of wetlands (Figure 9.5) and the taiga zone here is often referred to as a biome of forested wetlands.

Fig. 9.5 Vegetation of Western Siberia. Compiled by A. Tishkov using data from Sochava (1979)

Wetlands cover over 50 per cent of the West Siberian lowland and only in the easternmost areas, drained by the Yenisey tributaries, is the development of wetlands relatively limited. Watersheds provide optimal conditions for the accumulation of peat and the development of strongly acid peat bogs. Forests develop in proximity to rivers where drainage is better and, because of the exceptional swamping, they do not occupy large areas but stretch for great distances along rivers. Forests also occur on elevated drier sites in wetlands. However, these forests are sparse and tree growth is impeded. Five tree species dominate: Picea obovata, Abies sibirica, Pinus sibirica (all are dark taiga species), and P. sylvestris and Larix sibirica. Pinus sibirica does not require much warmth and grows well in areas with an excess of stagnant water. It is often found along the edges of peat bogs where its growth is impeded. The participation of Picea obovata is reduced in comparison with the European taiga because of the excessive supply of moisture. The broad-leaved tree species are absent, with the only exception of Tilia sibirica, which occurs in the undergrowth in the southern regions.

Similar to the European territory, a characteristic of the West Siberian northern taiga is low and open canopy with a cover between 30 per cent and 50 per cent (Agakhany-ants, 1986). Two types of forests, which are often swampy, with abundant dwarf shrubs and green mosses dominate: those composed of Picea obovata and those with two dominants, Picea obovata and Larix sibirica. Better-drained localities are occupied by forests comprised of Larix sibirica. In the north, they develop on sandy substrata which is otherwise uncharacteristic of Larix which prefers soils rich in lime. Towards the southern edge of the northern taiga, Pinus sylvestris develops on sandy soils.

The main forest-forming species in the middle taiga are Picea obovata and Pinus sibirica that occur in association with dwarf shrubs (Vaccinium spp., Ledum palustre) and green mosses (Pleurozium schreberi). The participation of Abies sibirica increases southwards. Similarly to the European taiga, herbaceous cover in the West Siberian middle taiga is very poor. In the north of the middle taiga, pine forests are common while in the south birch forests, which mainly represent secondary succession, are widely distributed.

The widespread occurrence of Pinus sylvestris across extensive areas makes it difficult to draw a boundary between the southern and the middle taiga subzones. In the southern taiga, the share of forested areas increases to approximately 60 per cent while areas occupied by wetlands become smaller. Forests are formed by the dark taiga species with Abies sibirica, the conifer most demanding of warmth, becoming increasingly important. Forests are distinguished by a taller and closer canopy. The green-moss forests develop on well-drained watersheds and associations with grasses and herbs occur on the slopes of river valleys. Undergrowth composed of Sorbus sibirica, Cornus alba, Sambucus racemosa, and large ferns (Matteuccia struthiopteris) develop in the forests growing in river valleys. Phytomass reserves and productivity of forests increase in comparison with the northern regions from 90 to approximately 230 t ha^-1 and from 5 to 6.5 t ha^-1 a^-1 (Bazilevich, 1993). The stands are mainly mature and the share of wood in total phytomass exceeds 75 per cent (Bazilevich, 1993: Bazilevich and Tishkov, 1986).

Extensive areas on the southern edge of the West Siberian taiga are occupied by birch forests. The stands composed of Betula krylovii, which reaches 25-30 m in height, are primary forests. Secondary birch forests also develop in burned sites.

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