The preserving of the genetic diversity of the forest types is the basis for sustainable management and conservation of the natural composition of the forests. Natural forests make up 95% of the total forests in Croatia and in its wealth geographic region contains different ecological types and a large number of the forest tree species. Global climate changes, rising temperatures, falling rainfall, occurrence of the extreme weather events directly affect on genetic diversity. The main objective of the proposed project is to make recommendations for the conservation of the genetic diversity of the forest trees. Precondition for achieving the goal is the identification and understanding of the genetic variability of the individual tree species. The research to be carried out by the project would be based on the common oak and beech. On existing genetic tests that were established at different sites, data on the survival and growth of plants, phenology, silvicultural properties, plant resistance to pests, etc should be collect. The stem forest stands from which the seed was taken will be used for collecting the data of health condition, fruiting and climatic parameters. The genetic diversity of the provenance will be analyzed by DNA markers. This project should be continued and expanded research on the identification of proven European beech resistant to drought, which are conducted in the framework of a bilateral cooperation with Germany (MSES-DAAD 2013/14) and the preservation of the gene pool and study of the variability of our most important tree species which are conducted as part of the project “Breeding and forest seed” supported by MSES of Croatia. From the economic point of view, the project aims is to raise the category of the forest reproductive material (FRM) in a higher category according to the Law of FRM (Official Gazette 75/2009, 61 /2011 – EU directive EC/105/99). Higher category guarantees a higher quality, and thus a higher price in the market.