Phytomass of Tree Fractions According to the Rank Distribution Model

One of the most important indicators of the condition of a tree is its phytomass. Its direct measurements (with cutting, drying and weighing) are very labour-intensive and have varying degrees of reliability. The data on root phytomass are the least reliable (especially for older trees, where direct excavation of the root system requires considerable effort). This necessitates the development of models for calculating the phytomass of fractions based on fairly simple reliably measured inventory characteristics. The article suggests using a free competition model to describe the structure of a tree when distributing resources available to the tree during growth between its fractions (stem, roots, branches, leaves or needles). The model allows calculating the ratios between the phytomasses of fractions. Based on these calculations, a method for estimating root phytomass has been substantiated. The differences in the parameters of the models for the distribution of fractions by phytomass for different tree species and different growth zones have been analyzed. To verify the correctness of the proposed model, data from the database by V.A. Usol’tsev (2016) on the phytomass of tree fractions (6,617 records) in Eurasian forest plantations have been used. The calculated rank distributions for 95 % of trees of various species of different ages growing in different geographical conditions have a coefficient of determination greater than 0.96, therefore, this model is of a general nature and describes well the relationships between the phytomass fractions of trees. The proposed approach significantly simplifies field measurements, but requires a preliminary assessment of the parameters of the equation of age dynamics for a particular species in specific climatic zones. Calculations of the competition coefficient for Scots pine (Pinus sylvestris L.) in Siberia in the territories of the Tomsk and Novosibirsk Regions, the Altai and Krasnoyarsk Territories based on the data from the database by V.A. Usoltsev show the proximity of the model parameters for trees of the same species growing in different conditions. The use of the developed model makes it possible to estimate the tree phytomass (including root phytomass) using such easily measurable indicators as tree height and stem diameter. An approach has been proposed for determining the phytomass of roots, in which, instead of excavating them, data on the phytomasses of the above-ground fractions of the tree are used.