The dissertation thesis deals with the design of a decision support system used in forest management planning. Dissertation thesis synthesizes both domestic and foreign knowledge of decision support systems, forest functions, indicators of fulfilment of forest functions and harvest-regeneration systems. The importance of the work is based on the fact that there does not exist complex decision support system in Slovakia providing the assessment of forest functions and forest management planning related to forest functions. In Slovakia, we have growth simulator of forest (SIBYLA), which is able to predict the development of forest ecosystems for several decades in future by using different forest management regimes. The outputs of Sibyla can directly serve as indicators of fulfilment of forest functions, which is a basis for the formation of decision support system.The designed decision support system consists of particular modules, which represent a complex system. It is comprehensive database of harvest-regeneration and thinning systems that can be performed within the legislation in Slovakia. Furthermore, there is module DBCreator which allows fast connection of the required forest stand structures with required forest management system. Automat module performs automated running of prognosis of forest ecosystem development and its calculation. The DBExtractor module synthesizes the results into a complex database needed for calculations. The Optimus is the last module forming a complex decision support system that optimize the outputs of growth simulator Sibyla. Optimus can select the optimal solution with maximizing required forest function or provide fulfilment of more forest functions, which is actually a typical requirement of forest management. The designed decision support system was used to assess the impact of tree species, site quality, thinning method, and harvest-regeneration method on the fulfilment of forest functions. What is more, the system evaluates the effect of discount rate as the most important economic factor on the fulfilment of forest functions. The designed system was used for the selection of optimal thinning and harvest-regeneration system in view of maximisation of selected indicators and harmonisation of all indicators in Forest Enterprise of University (Zvolen) and Community (Urbar) Forests Detva. Summarly, we performed 28,870 simulations (18,720 for thinning of homogenous forests; 5,200 for thinning of mixed forests; 4950 for harvest-regeneration systems), which would not have been possible without the particular modules forming the designed decision support system.The results of thesis showed that the designed system represents appropriate tool for assessment of fulfilment of forest functions and for forest management planning with the aim of fulfilment of required forest functions.