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Biomes and Regions of Northern Eurasia

Mixed and Deciduous Forests

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The Changing Nature of Forests

Over the 18th and 19th centuries, the share of arable land in European Russia increased from 20 per cent to 50 per cent (Mandych, 1989) and in the deciduous forest zone to 60-80 per cent (Isachenko and Shlyapnikov, 1989). Virgin forests were widely replaced by arable fields and meadows. In many areas, particularly in the deciduous forest zone, a new biome of agricultural fields was established. The structure and composition of forests have changed. The demand for high quality timber and selective cutting transformed pine-deciduous stands into forests dominated by small-leaved species, and locally into shrublands. Harvesting of oak, which represented the lower tier in oak-pine forests, has led to the development of pure pine stands (Walter, 1977). This may explain a broad distribution of pine stands in Polesye and Meshera. The widespread development of mixed forests has probably been supported by human activities which made a broader use of the original deciduous species than conifers. As a result secondary species, small-leaved trees and pine, became predominant. Small isolated patches of woodland replaced large massifs. At present, they constitute between 70 per cent and 80 per cent of the total forested area in the mixed and deciduous forest biomes (Mandych, 1989). Clearings are prone to swamping which is partly prevented by the use of clearings as pastures. The negative impact of cattle grazing is that it prevents the development of undergrowth and promotes the dispersal of weeds in forests. Forest fires are another natural and human-induced hazard that destroy large areas of woodlands, especially pine stands. The introduction of new species contributed to shaping the composition of contemporary forests. For example, in the Kaliningrad region alone about 500 new species have been introduced (Agakhanyants, 1986) and in Estonia more than 1000 (Valk and Eilart, 1974). Stands of Larix, represented in Estonia by more than 10 species, are the most typical example.

Similarly, in the southern Far East forests have been strongly affected by human activities and greatly damaged by fires of both natural and anthropogenic origin.5 Primary forests have been widely replaced by arable fields, shrublands, secondary stands of birch (Betula platyphylla), developing Quercus groves and, in wetter habitats, by Alnus and Salix stands, meadows and swamps. In the Amur valley, selective fellings of conifers favour the development of deciduous tree species. Oak often invades clearings which has led to a hypothesis of a young age for oak forests. However, palynological evidence has shown that oak was already widespread in the region by the late Pleistocene (Shumilova, 1962). In the west of the Amur valley, the typical secondary species is Carpinus.

In the Colchis lowland, the exploitation of forests and drainage has led to a massive decline in woodland and plant succession. Normal tree stands were replaced by procumbent trees and shrublands. Drained lands are covered by subtropical cultures, bamboo, and eucalyptus plantations. In the foothills, secondary forests are mainly represented by Carpinus. On the Talysh lowland, forests have been almost completely replaced by agricultural lands.

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