forests with a predominance of birch. In the USSR, they are prevalent primarily in the forest and forest-steppe zones and in alpine forest regions. Birch forests generally arise as secondary forest on the site of cutover or burned coniferous and mixed forests, as well as on abandoned plowed fields. The area of birch forests in the USSR amounts to nearly 92 million hectares—about 13 percent of the forest area of the country. The supply of birch lumber in these forests is about 6.8 billion cu m.
In the area of the most prevalent species of birch in the USSR (European white birch and Old World white birch), birch forests consist of European white birch on dry and drained soils and Old World white birch on moistened soils. Frequently both species grow together. The area of secondary birch forest is increasing as a result of concentrated cutting in the spruce and spruce-fir forests of the taiga zone, where renewal essentially proceeds with a replacement of species and cuttings of the younger generation are conducted with insufficient care. However, as a result of the birch’s exceptional need for light and the settlement of the indigenous conifers displaced earlier under its canopy, birch forests gradually become birch-spruce, birchpine, or birch-deciduous forests. One hundred years or more is required for the complete displacement of the birch and the reestab-lishment of the parent type of forest. It is possible to decrease this period through cuttings that increase the growth of coniferous-deciduous shoots. Birch forests which grow up on the site of coniferous forests are usually represented by the same types of wood as the coniferous forests were. Thus, whortleberry bushes, red whortleberry bushes, and mixed grasses, which make up 50–80 percent of the area of birch forests, are often found in birch forests and groves.
Indigenous birch forests are encountered in smaller areas, in moist, depressed places. These are the cane and reed grass sedge (with Calamagrostis langsdorfii in the mantle), sphagnous birch forests, and also the birch groves of western Siberia, which consist essentially of European white birch, with a mixture of Old World white birch in sinks. The birch forests of eastern Siberia and the Soviet Far East are made up of different species of birch; they cover several million hectares and are of great value. Tidal paper birch and paper birch on slopes are distinguished. Forests of Betula ermanii grow over vast areas between Baikal and Kamchatka and on the Komandorskii Islands. Vast thickets of shrub birch—dwarf, Betula exilis, Betula middendorfii, Betula humilis, and other varieties—are encountered in bog and sphagnum swamps.
A. P. SHIMANIUK