the basic unit for classifying plant cover and representing the aggregate of uniform phytocoenoses with the same structural and specific composition and with similar relationships both between the organisms and between them and the environment. Each association is closely related to certain environmental conditions, such as climate and soil, as well as the animal life that inhabits it. An association is characterized by a definite productivity (supply and increment) of the plant mass. Associations change with a change in environmental conditions and composition of the flora. Thus, the modern European associations of broad-leaved forests arose from the Arcto-Tertiary forests and can in turn give way to other associations in the course of the historical development of the vegetation. Under the influence of changes in the topography and in hydrological and soil conditions, and as a consequence of anthropogenic influences, both direct (for example, haying, timber-felling, and the construction of man-made bodies of water) and indirect (for example, the pasturing of livestock), areas of present-day vegetation can be fundamentally changed.
Some examples of associations are pine forests with cowberry in the ground cover on dry and poor soil, pine forests with whortleberry on wetter soil, oak stands with goutweed in the grass cover, meadow areas with a predominance of foxtail and an even distribution of other plants, bogs with a sphagnum cover, cotton grass, marsh tea, and so forth.
The properties of the dominant associations are used as the bases of assessing the forest and feed lands. For example, in detailed studies of meadows and in the compilation of large-scale maps of vegetation cover, individual associations are plotted on them. (Groups of associations are plotted with a reduction in the scale.) Associations are usually named after the dominant plants in them—for example, pinetum-cowberry is Pinetum vacciniosium, and a spruce-pine forest with cowberry and oxalis is Piceto-Pinetum vaccinioso-oxalidosum. Russian and Soviet scientists such as G. F. Morozov, V. N. Sukachev, V. V. Alekhin, and A. P. Shen-nikov have made great contributions to the study of plant associations.
REFERENCESRastitel’nyipokrov SSSR, vols. 1–2. Moscow, 1956.
Osnovy lesnoi biogeotsenologii. Moscow, 1964.
V. N. SUKACHEV