The branching orders of the crown of virginal tree of Ulmus glabra Huds

Abstract

Tree crown formation in ontogenesis is a realization of spatial and temporal development program. Based on the study of young individuals of U. glabra growing in a natural oak forest, the presence of two groups of axes was shown. One group creates the axes of crown base - “skeleton”. The other one appears at a certain age and creates the so-called “crown lace” - a short-lived and replaceable base for photosynthesis. The transition from the formation of the skeletal part of the crown to the next stage, which occurs in the 4th branching order, the shoots of which are significantly shorter, and their number is greater, is quantitatively shown. It is shown that the lengths and number of leaves on shoots in the axes of the first three orders of branching vary within a large range. The maximum variability is reached on the third order of branching, after which it decreases. When crown development reaches the 4th order, spatial growth limitations, which are determined by angles of shoot branching, leaf size, lifetime of axes and shoots, begin to play their roles. Here, more structured crown space is required to optimize the photosynthetic surface.