Age-Related Changes in the Ratios of the Components of Aboveground Phytomass of Forest-Forming Species of Eurasia

The assessment of phytomass, as the most important characteristic of forest ecosystems, plays a key role in monitoring the global carbon cycle and assessing the state of forests. In order for the species to achieve optimal productivity at the plant level, some proportionality between the functions and phytomass of its components must be ensured. The theory of optimal phytomass partitioning suggests that plants adapt the size of their organs not only to the external environment, but also to the physiological activity of various tissues. According to this theory, it has been established that the share of the component in the total phytomass (i.e., the relative phytomass of the component) is not constant: if in mature trees the largest share of phytomass falls on the stem and the smallest on the assimilation apparatus, then in seedlings the largest share of phytomass falls not on the stem, but on the assimilation organs. In order to establish the age at which the aforementioned trends change, the author’s database on the phytomass of trees belonging to the forest-forming genera of Eurasia was used. Models of changes in relative phytomasses for four coniferous and four deciduous forest-forming genera have been developed in relation to the tree age and the aboveground phytomass. Their contributions to the explanation of the variability of relative phytomass components amounted to 57–60 and 40–43%, respectively. It is established that with tree age the positive dependence of the relative phytomass of the stem upon the aboveground phytomass is replaced by a negative one, and the negative dependence of the relative phytomass of the branches is replaced by a positive one. The negative dependence of the relative foliage mass upon the aboveground phytomass by the age of maturity is leveled. The ages of the change of the positive or negative dependence of the relative phytomass of the components upon the aboveground phytomass by the opposite dependence in the studied age range have been established. However, the ages of the replacing these rankings vary greatly in different genera, and further research is needed both to clarify the ages of the named shift and to clarify the reasons for such a significant variation. The obtained results showed that the relative phytomasses of the components change with age and phytomass in their interaction, i.e. there is a synergy of factors.