Summary: At the beginning of the millennium we passed from the epoch of single-purpose into the epoch of multi-purpose forest management. Forest economy requires that a forest as a natural wealth and an economic resource permanently satisfy growing needs of the society (multiple use). This overall requirement may be satisfied only by a forest of optimal form and sustainable growth.During scientific research of many years into the most favourable management procedures relating to the conversion of forests stands of selection silvicultural form into an optimal condition, prognostic models of sustainable development and management have been created based on the principles of imitating the nature.Two Croatian systems of optimal models – normal models may be applied to management of selection forests. Both systems are identical in purpose – to convert a degraded real condition into a normal (optimal) condition, but different in organisational elements and conversion procedures. Normal models by Ecological Management Types (EMT) have been constructed to convert forests in terms of forest types and subtypes, while the New System normal model is based on site classes.The analysis of the organisation of both systems has shown that certain elements of constructing EMT normal models are not compatible with the age structure of trees in selection stands. In optimising the scientifically objectively selected forest types and subtypes, the time elements of the construction: rotation, diagonal age (average) increment, absolute maturity, stand cutting maturity determined by the data in the corresponding growth-yield (GY) tables, as well as natural site productivity expressed by unified normal tree series, are questionable in terms of application. The disputable construction elements stem from the basic postulate of the system – identifying trees with stand maturity - which is debatable due to differences in the developmental dynamics of diameter and age structures, and consequently determining stand maturity of even-aged stands in relation to tree maturity of stands of selection silvicultural form.The paper presents scientific insights into theoretically debatable elements of optimisation by applying EMT normal models (partially of empirical origin) and proposes a solution and objective application.
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