THE ECOLOGICAL SIGNIFICANCE OF THE BIOMECHANICAL PROPERTIES OF WOODY PLANTS ON THE EXAMPLE OF JUNIPERUS VIRGINIANA L
The paper presents data on the ecological and biological effects of temperature changes on elasticity modulus of wood (Е) in Juniperus virginiana L. When passing to high temperatures, tree resistance to stress is reduced. Loss of elasticity causes uneven rigidity losses along the trunk or shoots reflected in branch union angle of skeleton branches with the trunk, i.e. in architectonics. In its turn, this fact affects the crown projection area, light permeability, and as a consequence, the temperature and water regimes under the canopy. The study has shown that in clear weather the intensity of total illumination under the pencil wood canopy in check tree clumps is significantly lower than in the trial. In the plots of openings under the canopy the clear-day illumination was ~40-60(max) % for the trial plots and ~4-5(max) % for the control areas. The air temperature in the canopy was at by ~30% lower in the check plots than in the experimental areas, he upper soil layer temperature being less by 19%. The sufficient solar radiation intake by experimental tree groups reduces their hardiness and, as a consequence, accounts for colonization by grasses and shrubbery vegetation. The allometry and tree biomechanics researches have indicated that at d/l coefficient less than 0.01 the few kilogram load or even self-weight become critical for the tree and causes irreversible trunk and shoot bending or even fall of the whole organism. This load can easily be reached with summer temperature rise up to 40<sup>o</sup>C and consequential elasticity modulus fall. When affected by dynamic factor such as the wind, the critical load is reduced by extra 20%.