The succession of terrestrial ecosystems (seres) is studied in aspects of structure, function, production and energetics of the participating organisms. All aspects mentioned involve history and evolution of the communities integrating the ecosystems.
The first approach is the structure, which is particularly dealt with in the present paper. Obviously, most knowledge of ecosystem succession regards the first step only. It indicates the need of study of other aspects, also, and a want for a clear image of structure.
Birds and mammals take part in almost all terrestrial ecosystems. Within the seres of a particular succession-primary and secondary we recognize three, mainly dynamically defined groups of higher vertebrates named, viz. 1) progressive species entering populations, 2) regressive, disappearing species and 3) conservative constant species populations, called in the present paper the core of series.
Some problems of structure, the sources from which group 1 penetrates and the function of the particular groups are there dealt with, based on author's own materials and data from some literature.