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Biomes and Regions of Northern Eurasia

Boreal Forests

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Forest-tundra and Northern Open Forests

The forest-tundra ecotone extends across Russia from the Kola peninsula to the Chukchi peninsula (Figure 9.2).

Fig. 9.2 Subzones and longitudinal sectors within the taiga zone

It is best expressed on the plains of Western and Central Siberia, while in the mountainous regions of northeastern Siberia, open Larix forests with thickets of dwarf Betula and Pinuspumila dominate. The spatial change in tree species forming the northern tree line is controlled by historical (i.e., glaciations and marine transgressions) and ecological (climate, relief, bogging and soil fertility) factors. However, the most important controls are air temperature and the temperature of the uppermost layer of soil, which determines the availability of nutritious solutions to trees (Tyrtikov, 1995). Among the woody plants of the forest-tundra, the resistance to low temperatures and effects of permafrost changes from high to low in the following order: Larix gmelinii —> L. sibirica —> Alnaster fruticosus —> Pinus pumila —> Picea obovata —> P. abies —> Betula tortuosa —> other species.

In the Kola peninsula, forest-tundra is dominated by Betula tortuosa with a participation of Picea abies. Small patches of woodland alternate with shrubby tundra represented by the genera of Vaccinium, Ledutn, and Empetrum. On the plains of the European north, the forest-tundra zone is 100-200 km wide. Winters are more severe in this region in comparison with the Kola coast and woodlands are composed mainly by the cold-resistant Picea obovata with a participation of Picea abies and Betula tortuosa. Woodlands alternate with southern tundra ecosystems represented and dominated by shrubs, mainly Betula ïàïà with an admixture of Salix, dwarf shrubs (Vaccinium spp.) and mosses.

In Western Siberia, two provinces are distinguished within the forest-tundra. In the western province, which extends from the Urals to the river Taz, woodlands composed of Larix sibirica alternate with shrubby tundra. The absolute heights do not exceed 50-80 m above sea level and drainage conditions are very poor which predisposes the widespread development of wetlands. In the easternmost part of this province, sandy deposits are more common and in the conditions of better drainage Picea obovata-Betula and Picea obovata-Larix sibirica woodlands, otherwise more typical of northern taiga, develop on southern slopes. The eastern province, located between the Taz and the Yenisey, is more elevated and dissected with absolute heights ranging between 120 m and 180 m. Bogs develop on the watersheds while on better-drained slopes woodlands formed by Larix sibirica or by Larix sibirica and Picea obovata occur. A distinguishing feature of the woodlands formed by Larix sibirica is the domination of lichens. These woodlands, similarly to the open forests of Central Siberia, are termed 'lichen woodlands'. The tree line in Western Siberia is located to the south of the modern ecological limit of tree growth apparently because of the recent retreat of the ice shield (Agakhanyants, 1986).

In Central Siberia, forest-tundra and open forests reach their largest latitudinal extent. The main tree species here is Larix sibirica. Relatively high, about 13°C, summer temperatures on the lee side of the Putorana plateau, which shelters the region from the northerly winds, allow forests to penetrate further north than anywhere in the world. On the Taymyr peninsula, woodlands (known as 'forest islands' Ary Mas and Lukinsky) formed by Larix gmelinii extend to the world's northernmost location at 72°30'N in the valley of the river Novaya, the Khatanga's tributary. Trees reach a height of 4-5 m and about 80 per cent of them are over 200 years old. Both woodlands are protected by the Taymyrsky nature reserve.

The position of the northern tree line changes over time. Both variability and processes controlling it differ across Northern Eurasia. In most regions over the last few decades the tree line has migrated southwards and the tundra communities have advanced mainly in response to deforestation, frequent forest fires (including those of human origin), and damage inflicted by the growing reindeer herd (Tyrtikov, 1995).

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