subdivisions of a physical geographic zone (see ). A physical geographic subzone is formed within a zone as a result of gradual changes in the climate, hydrological conditions, geochemical and soil-forming processes, and the primarily longitudinal structure of the biocenoses. Such a subzone is characterized by the predominance of one or another type of landscape. For example, the equatorial forest zone has subzones with and without a brief dry period; the boundary between the subzones is usually indistinct. Within the subzones there usually are transitional indications of the adjacent subzones and zones; for example, in the northern taiga of forest communities, well-delineated areas of tundra are encountered.