The paper deals with assessment of fir growth on four research plots in Slovakia situated in mixed spruce, fir and beech stands, where no interventions have been carried out during last 30 years. The results showed the high decrease of fir, which was 76-89% out of the number of trees. On the contrary, the highest proportion on each plot during investigation period has been registered for beech, which shifted into the dominant canopy layer whilst the middle canopy layer comprised of fir and spruce. As for mean crown width the low, as well as statistically insignificant differences among tree species were found. The crown width in relation to diameter increment of tree species was the closest on each plot for beech, and the correlation was found statistically significant (P < 0.01), too. For fir and spruce, lower values of coefficient of correlation were found, while they were not always significant. The highest mean annual diameter increment was registered for spruce and the lowest for fir. The above-mentioned outcomes suggest that beech is characterized by strong competition ability in comparison to other tree species under the given ecological conditions.