EN
A new theory of processes occurring in forests of the varied structure of breast-high diameters is presented in the work. The two processes differentiated and defined are the survival and the decrement, the measurability of their intensity being determined. The identified processes were used in formulating the model of development of a forest management class characterized by a varied structure of breast-high diameters, in the form of the probability matrix of transitions. Such a matrix constains a complete information concerning the effect of the survival and decrement processes on the sustainability and balanced development of forests of the varied structure.