Features of a Biennial Shoot System as a Unit for Modeling Crown Development in Ulmus glabra Huds

Abstract

This article presents the results of studies on the structural organization of the crown in Ulmus glabra. Knowledge of types of shoot systems regularly changing in the tree crown in the ontogenesis of a species is of both theoretical and practical importance. In our studies, we use an architectural (modular) approach that enables us to describe the spatiotemporal program of tree-crown development. The results show that the main structural unit of the tree crown, resistant to the changes in climatic factors, is a biennial shoot system (BSS). The choice of this unit is determined by the fact that zonality in maternal shoot can be detected only in the second year of the shoot lifespan. To identify the spatiotemporal structure of the BSS, we have compared the traits of 1- and 2-year-old shoots. The BSS of U. glabra undergrowth plants in the forest-steppe oak forest of the Belogorye Natural Reserve have been studied. The study involves 100 species of the same ontogenetic stage. The shoot systems in the studied trees have been differentiated into large (“growth”) and small (“basic”) ones with the same location within the crown. Based on the cross-correlation function, which depends on the internode number on the maternal shoot, a regression model of the length distribution of lateral shoots has been created. It is shown that, when numbering the internodes on the maternal shoot from the top downwards, the dependence of the lateral shoot length of both the growth and the basic BSS in U. glabra vs. the number of internodes is consistent with the exponential model. The development of the BSS is found to be dependent on the light conditions and positioning in the crown. The comparison of two samples allows us to introduce a shift parameter into the model, which defines a specific zone in the maternal shoot.