The article presents the results of a study of the structural organization of the crown of Ulmus glabra . Knowledge of the types of shoot systems that regularly change in the tree crown in ontogenesis of an individual is of theoretical and practical value. In our studies, we used the architectural (modular) approach, which allowed us to describe the spatio-temporal program of tree crown development. The results obtained allowed us to determine that the main structural unit of the crown, resistant to changes in climatic factors, is a biennial shoot system. The choice of this unit is due to the fact that the zonality of the maternal shoot is only detected in the second year of its life. To identify the spatio-temporal structure of a biennial shoot system, the characters of shoots of the first and second years of life are compared. The biennial shoot systems of undergrowth plants of U. glabra were studied in the forest-steppe oak forest of the Belogorye reserve. 100 individuals of the same ontogene