or geography of the vegeta-tional cover, the branch of knowledge which studies the veg-etational cover as a component of the geographical landscape. In contrast to plant geography, which studies the distribution (range) of species or other systematic categories of plants and their regional complexes, or flora, botanical geography relies on the data of geomorphology, soil science, climatology, and other sciences, as well as the data of geography, plant ecology, and phytocoenology. Botanical geography is close to geobotany in content. Generalizing data on the distribution of vegetation (especially, the types of vegetation) on a broad plane, botanical geography is of great cognitive and practical significance. Its data are used in planning agricultural development of lands, in developing forest and water resources, and in carrying out natural and economic-geographical regjonalization.
Some elements of botanical geography are found even in the works of the ancient geographers, such as the Greeks. But the first works of botanical geography proper date from the 18th century. Among these works, a prominent place is held by the expeditions of the St. Petersburg Academy of Sciences, described in the works of J. G. Gmelin, S. P. Krasheninnikov, P. S. Pallas, and I. I. Lepekhin, among others. The most important positions of botanical geography were formulated by the German botanist and geographer A. Humboldt at the beginning of the 19th century. The subsequent stage of its development came with the works of the Danish scientist J. F. Schouw (1823), the Swiss botanist A. de Candolle (1855), and the German botanist A. Grisebach (1872), among others. The development of botanical geography was especially aided in Russia by the works of such scientists as F. I. Ruprekht, K. I. Maksi-movich, A. F. Middendorf, A. N. Beketov, V. V. Doku-chaev, S. I. Korzhinskii, A. N. Krasnov, A. Ia. Gordiagin, P. N. Krylov, V. L. Komarov, J. K. Paczoski, and G. I. Tanfil’ev. Works on botanical geography were particularly widely developed after the October Revolution. Intensive study of the tundras, forests, marshes, meadows, steppes, deserts, and vegetation of mountainous areas added new data to enrich the theory of botanical geography and the practice of national economy. An important role in this process was played by the work of V. V. Alekhin, B. A. Keller, B. N. Gorodkov, A. P. Il’inskii, N. I. Kuznetsov, V. N. Sukachev, A. A. Grossgeim, E. P. Korovin, and others.
Terrestrial vegetation is characterized by latitudinal zones which are subordinate to the climate zones. This is expressed more sharply in the northern hemisphere. In the areas farthest from the equator are the treeless arctic deserts and tundra. To the south of them are coniferous forests, then the deciduous forests and the hard-leaved evergreen forests. In the continental interiors the hardwood forests are replaced in large areas by steppes. Further south there are desert belts. Further south in the tropical latitudes, tropical rain forests alternate with arid sparse forests and savannas; such an alternation is explained mainly by the differences in moisture conditions in a hot climate. To the south of the equator the zonal vegetation changes are repeated in reverse order, but they are expressed incompletely and less clearly as a result of the limited and broken land area. The distribution of vegetation within the boundaries of each latitude zone is determined by such factors as the distance from the given area of land to the sea, the direction and intensity of the prevailing winds, and the presence of significant mountain systems and ranges which can block the passage of moist air masses to the continental interior. The distribution of vegetation is also influenced by the exposure of slopes, the ease or obstruction of water flow, and the soil conditions.
A most important factor which complicates the distribution of vegetation in each latitude zone is the altitudinal, or vertical zonation which is caused by climatic (mainly temperature) changes, depending on the altitude above sea level. Substantial changes in the character and distribution of vegetation are linked with the influence of man’s economic activity, especially in areas which have been settled for a long time or which are densely populated. In the Mediterranean countries, Central Europe, southern and eastern Asia, and a number of other areas, the vegetational cover has only here and there preserved its original character, or one close to it. Often it is replaced by cultivated plantings—such as fields, gardens, and the complex of vegetation of oases in irrigated parts of the desert—or by so-called secondary growth formation, which grows in the place of cut-down forests or drained swamps. Such secondary growth formations are exemplified in a significant part of the meadows of the temperate zone, the shrub undergrowth, and part of the savannas.
There is no generally accepted system for typing the vegetational cover. All the classification systems are based on traits related to plant ecology, and partly on the systematic composition of plant communities.
In the USSR, with its variety of topographic, climatic, and soil conditions, practically all the types of vegetation of the cold and temperate zones are represented. The zonal distribution of the basic types of vegetation is seen particularly clearly in the USSR in the European part, Western Siberia, Kazakhstan, and Middle Asia. The study of laws of zonal vegetation distribution in its connection with the climate and soil zonality makes up a substantial part of the works of Russian and Soviet scientists in the field of botanical geography. Usually the following zones are distinguished: arctic desert, tundra, forest tundra, taiga with subzones of coniferous and mixed coniferous and broad-leaved forests, broad-leaved forests (only in the European part of the USSR and the Far East), forest steppe or presteppe, steppe, desert steppe or semidesert, and desert. For each zone a particular system of vertical zones is characteristic for mountain vegetation.
The composition of vegetation depends not only on the basic laws of its distribution, caused by the influence of the environment, but also on the history of the development of the vegetational cover. The composition of flora, in particular, is linked with this history.
One of the most important forms of generalizing data on the earth’s vegetational cover is the use of maps of the vegetation, or geobotanical maps. Their detail and their principles of showing plant distribution depend upon the scale. Depiction of “reconstructed” vegetational cover—that is, the types of vegetation which existed on land not exploited by man—is given on small-scale maps. Representation of the distribution of natural types of vegetation as well as of various types of land transformed by man is possible only on large-scale maps, which reflect the present-day condition of the vegetational cover more accurately and in more detail. In the development of vegetation cartography a large role was played by the unfinished edition (begun in 1921) of the Map of the Vegetation of the European Part of the USSR, on the scale of 1:500,000, which was compiled under the direction of N. I. Kuznetsov and Iu. D. Tsinzerling, and by the Geobotanical Map of the USSR, on the scale of 1:4,000,000 (edited by E. M. Lavrenko and V. B. Sochava, 1956), with two volumes of explanations. Another substantial form of generalizing data about the vegetational cover is botanical-geographical (geobotanical) regionalization. Its principles were worked out in the USSR by A. P. Shennikov, P. N. Krylov, B. N. Gorodkov, A. A. Grossgeim, and E. M. Lavrenko, among others. The result of the application of these principles to the USSR as a whole was a compendium of the geobotanical regionalization of the USSR (1947). The largest regional unit in this work is the oblast, and the following oblasts are distinguished: the Arctic tundra, European and Siberian shrub region (forest-tundra), Bering shrub region (forest-tundra), Eurasian coniferous forest (taiga), Far Eastern mixed coniferous and broad-leaved forest, Kamchatka hardwood forest with a grass layer, European broad-leaved forest, Mediterranean forest, European-Siberian forest steppe, Eurasian steppe, and Asian desert. The oblasts are subdivided into provinces (in some cases intermediate categories, suboblasts, are introduced), and the provinces are further divided into okrugs. In the territory of the USSR, 384 botanical-geographical okrugs have been established.
A more detailed regionalization has not been applied to the USSR as a whole. It exists for individual parts of the country, for example, the work of Iu. D. Tsinzerling for the Northwest European USSR, the work of A. P. Shennikov for the Northeast European USSR, and the work of A. A. Grossgeim for the Caucasus; but the principles of such detailed regionalization do not always coincide in the works of various authors. The botanical-geographical raion is taken as the smallest and basic unit of detailed regionalization.
Work in botanical geography is carried out in the majority of countries by botanical (rarely special botanical-geographical) institutes of academies, universities, and sometimes of bureaus studying the development of agriculture and forestry. In the USSR such work is carried out by the botanical institutes of the Academy of Sciences of the USSR, its branches, the republic academies of sciences, and also botanical (and special geobotanical) subdepartments of universities and other institutions of higher learning, as well as institutes and offices of agricultural and forestry bureaus. The results of botanical-geographical scientific work are used by the USSR Gosplans (State Planning Commissions) and those of the Union republics, by ministries of agriculture and forestry, and others.
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V. N. SUKACHEV