Features of the structure and development of the crowns of woody plants of the genus Robinia L

Abstract

The most important element in the formation of the habit of woody plants is the size and shape of the crown. Designing decorative compositions in landscape gardening is possible only taking into account the peculiarities of the structure and development of crowns. In the generic complex Robinia L. there are four species and several decorative forms of woody plants, which differ significantly in the structure and features of the development of crowns. The design of landscape compositions using these plants is complicated by the fact that they are all capable of forming different types of crowns, depending on the ecological conditions of growth in the process of ontogenetic development. In this regard, the purpose of this work was to study the features of the structure and development of crowns of representatives of the genus Robinia in different environmental conditions. The objects of research were species and forms of the genus Robinia L .: R. neomexicana Gray .; R. pseudoacacia L .; R. pseudoacacia f. pyramidalis (Pepin) Rehd .; R. pseudoacacia f. umbraculifera (DC) Rehd .; Robinia viscosa var. hartwegii (Koehne) Ashe .; growing in the dendrological collections of the Federal Research Center of Agroecology of the Russian Academy of Sciences, inventory No. 34: 34: 000000: 122, 34: 34: 060061: 10. Studies have shown that the formation of crowns is influenced by a genetically determined architectural model, as well as environmental factors of the habitat, the main of which are: hydrological regime, illumination and wind load. The formation of a certain life form under the influence of the hydrological regime leads to a change in the general geometry of the crown, uneven lighting leads to an increase in asymmetry, and an increased wind load reduces the overall density of the crown. It was found that for R. pseudoacacia with the life form of a single-stemmed tree, a spreading crown shape is typical, and for R. neomexicana and R. viscosa - narrow oval and domed, respectively. The multi-stemmed life forms of R. neomexicana have predominantly rounded-toothed crowns, while R. viscosa has rounded-domed crowns. The crowns of R. pseudoacacia with a change in life form, as a rule, change only the general geometry, while maintaining a spreading shape. The formation of this type of crown is caused by the large size of the plants of this species. The large height and diameter of the crown leads to an increased wind load (Chan W., Eng Y ..., 2020; Bunce A., Volin JC, Miller DR, 2019), to reduce which, in the course of evolution, a spreading crown with a high degree of openness was formed (the gaps are 60-70%). It was revealed that strict geometric spherical and columnar forms are characteristic only for decorative forms of R. pseudoacacia f. umbraculifera and R. pseudoacacia f. pyramidalis, and high-stemmed forms are formed in plants after radical rejuvenating pruning at a height of 3-3.5 meters. R. pseudoacacia, after radical rejuvenating pruning, forms a rounded-oval shape, R. neomexicana - a rounded-upper-oval shape, and R. viscosa - a wide-domed or even umbrella-domed shape. Analysis of architectural models made it possible to determine the main patterns of the formation of crowns of various types. Thus, in the development of the domed crown of R. viscosa, the determining factor is the genetic predisposition to the formation of obliquely drooping overgrowing branches. Ascending and inclined shoots of R. neomexicana at a relatively high crown density (gaps are 50-60%) lead to the formation of a narrow oval crown shape. During the implementation of the genetic program of development, in R. pseudoacacia, skeletal branches are predominantly formed, ascending at an angle of (45) 50-70 degrees, and in R. viscosa and R. neomexicana at an angle of 60-80 (85) degrees. The results of the studies have shown that the crowns of all species undergo significant transformation in the process of ontogenesis. In blueness specimens of single-stemmed trees, the asymmetry increases significantly, the crowns acquire a spreading or flag-like shape. Further aging processes lead to the loss of the central conductor and the transformation of the life form into a multi-stem aeroxyl or geoxyl tree. It was found that the crown density of all studied Robinia species has a pronounced seasonal and diurnal dynamics. Seasonal dynamics is determined not only by autumn, but also by summer leaf fall. Daily fluctuations in density occur due to thermonastic movements of complex leaves