Mechanical stability of Fagus sylvatica L. in the conditions of the south of the East European Plain: the theory of loss of stability

The paper considers the issues of ecological and biological features of the growth of the European beech in the territory of the steppe zone of Donbass in the conditions of the south of the East European plain. Taking into account the changing climate over the past 10 years, the issues of resistance of introduced species to temperature changes, the effects of snow and ice storms occurring within the seasons are becoming relevant. It was found that the greatest damage, from an ecological point of view, the plant experiences with sudden changes in weather conditions within the season (cyclic processes of freezing/thawing) and uneven heating of wood tissues during thawing, which locally reduces their physico-mechanical properties. As a result, the trunk or skeletal branches lose the property of relative uniformity. The uneven rate of change in mechanical properties leads to a loss of rigidity and increased stress, the upper part of the trunk becomes an additional glaciated mass, while the load on the thawed area approaches critical. The described effects are explained by the state of water in the vessels of woody plants. Thus, in the freezing/thawing cycle (seasonal phenomena), the phase state of free water and, as a result, its physical properties change. When passing through 0°C, ice melts in portions, which over time leads to an uneven decrease in the modulus of elasticity of the wood. As a result, the physical and mechanical properties of wood differ in different parts of the volume and change rapidly during the transitions of water from the solid phase to the liquid phase. The environmental consequences of this phenomenon are irreversible deformations of plant organs, a change in the architectonics of the crown and the angle of inclination of the trunk, in extreme cases, a fragment of the trunk and skeletal branches.