The thesis is focused on the natural forests and their characteristics, development and structure. The thesis describes natural (primary) forests located in the 7th spruce forest vegetation zone. Further important aim of the thesis was to find out and compare the changes in crown parameters in spruce stands with changing altitude. Measurement and subsequent comparison was carried out in two altitude zones. The first and second measurement was carried out in the altitude below 1,350 m a.s.l. and above 1,400 m a.s.l. respectively. Individual measurements were carried out in the national nature reserve Zadná Poľana. In 2013, 20 permanent research plots were established on Poľana, specifically in the areas 526 and 527, where these measurements were carried out. The research plots had circular shape, and their area was 1,000 m2 with the diameter of 17.85 m. Living and dry standing trees were measured; the data were subsequently used for calculating the spruce crown dimensions while these values were considered average for the entire plot. The final values and differences between individual altitudes were evaluated using descriptive statistics and via testing the differences using the software Statistica 6.0.