BIBLIOGRAFIC REFERENCE Kloska, O. 2021. Selected Features of the Structure of Natural Spruce Forest in National Nature Reserve Poľana and Babia hora: Master thesis – Technical University in Zvolen. Faculty of Forestry, Department of Silviculture. Master thesis supervisor: Assoc. Prof. Ing. Peter Jaloviar, PhD., Zvolen LF TU, 2021, 50 p. The present thesis is focused on describing the characteristics of two natural forests. These natural forests are located in the 7th vegetation spruce zone. They are primeval forests (virgin forests) located in the National Nature Reserve Poľana and in the region of Orava (National Nature Reserve Babia Hora). The objective of the thesis was to compare the basic stand characteristics in spruce natural forests and find out the impact of various disturbance factors on the diameter and height structure as well as density of the selected stands. The main differences should be apparent in the diameter distributions and in the height structure of the stands, as well as in the number of individuals. In 2013 permanent research plots were established in the selected nature reserves Poľana and Babia hora with the area of 1,000 m2. The aim was to collect data from repeated measurement of dendrochronological analyses. In the National Nature Reserve Poľana a network of 20 permanent research plots was established and the plots were located in the plots no. 526 and 527. In the National Nature Reserve Babia hora 10 permanent research plots were established in the plots no. 1241 and 1244. The position of all trees was localised in selected plots (living trees, snags). 6 plots in the highest vegetation belt of Poľana, located at the altitude above 1,400 m ASL and 6 plots in the location of Babia hora with the altitude above 1,350 m ASL were selected for the assessment. It was found out that the diameter distribution in the National Nature Reserve Poľana is bimodal, and in the stand, there is two times higher number of trees per 1 ha of area. In the National Nature Reserve Babia hora, intense damage to the stand caused by insects can be observed, while probably only the most vigorous trees of the higher stand layer with sufficiently long crowns survived the insect damage.