MODELS AND TABLES OF THE PHYTOMASS OF DEAD BRANCHES IN GROWING TREES OF SCOTS PINE AND SILVER BIRCH IN THE STEPPE ZONE

Under conditions of a changing climate, the relevance of assessing the full carbon pool of all components of forest ecosystems increases, not only of the living aboveground and underground parts, but also of litter, large detritus, soils, etc. There are numerous estimates of the phytomass of the aboveground part of forest trees and stands, both taking into account the mass of branches that have died and preserved on tree stems, and without taking them into account. There is no information about the mass of dead branches on tree stems in the available databases on the phytomass of trees. Thus, the mass of dead branches of trees and stands is not included in the calculation of both the input and output components of the carbon cycle, and when estimating the carbon pool of forest ecosystems, it is underestimated by some unknown amount. In the published data on the phytomass of trees, the relative mass of dead branches, i.e. the ratio of the mass of dead branches to the aboveground phytomass, varies from 0.1 to 26 %, however, attempts to identify factors explaining such a wide range of it are quite rare. In this study, the first attempt was made to develop allometric models designed to estimate the mass of dead branches of growing trees of Scots pine ( Pinus sylvestris L.) and silver birch ( Betula pendula Roth) in the conditions of the steppe zone. The study was based on 465 model trees obtained on 35 sample plots. It was found that in the mature birch stand, the mass of dead branches is 1.32 t/ha and relative mass of dead branches is 2.5 %, in natural pine forests 0.9-17 t/ha and 0.7-13 %, respectively, and in plantations 0.2-13 t/ha and 1.3-11 %, respectively. The dependencies constructed for the relative mass of dead branches are combined with yield tables of the aboveground phytomass of stands of natural origin and plantations of the Turgay Depression. It was found that, depending on the origin of the stand, its age and site index, the relative mass of dead branches varies from 0.8 to 15 %. The proposed allometric models and inventory tables can be used in the assessment of the mass of dead branches on tree stems of pine stands. When calculating carbon pools in the forests of the steppe zone, it is necessary to take into account the mass of dead branches by applying increasing coefficients in pine forests from 0.8 to 15% and in mature birch forests 2.5 %.