[Succession in forest coenoses: a model of second-order phase transition].

The changes of arboreous coenoses composition resulting from natural and anthropogenic impacts are considered. The mathematical model is proposed and verified that describes arboreous cenoses transition from one succession state into another by analogy with phase transition in statistical physics. It is demonstrated that the model is concordant with the data of full-scale observations. The model allows to explain the trend of succession processes and determine the stage of forestation process at which succession transitions should be expected. The analysis of full-scale observations data by means of the proposed approach makes it possible to calculate, for given regions and forest types, the critical values of planting phytomass that, upon being attained, initiate the succession transition. Those values are important to be known for middle- and long-term forecasting of forest cover dynamics.