The mountain spruce forest in the Lopučnica valley is located in Triglav National Park and is part of the Savica-Ukanc forest reserve. After abandoning managment since 1883, it has been left to natural development. After 39 years since the first measurement (Cvenkel and Mlinšek, 1983) and 24 years since the second measurement (Poljanec, 1998) we repeated the measurements on a permanent research plot in the Lopučnica valley, which was established by Cvenkel in 1983 as part of research on forest reserves in Slovenia. The purpose of the thesis is to present the changes in the structure and development of the mountain spruce forest in the period 1983-2022. We quantified mortality and recruitment rates in two periods: 1983–1998 and 1998–2022. The tree composition remained unchanged during the observed period. The basic stand indicators for 2022 had the following values: N = 388 trees/ha, G = 57.60 m2/ha, V = 675 m3/ha. The annual mortality rate increased from 1,3 % in 1983–1998 to 1,5 % in 1998–2022. The annual mortality rates for both observed periods had a similar pattern, with the highest values in the smaller diameter classes. The annual recruitment rate decreased from 0,06 % in 1983–1998 to 0,04 % in 1998–2022. Annual recruitment rates for both studied periods were highest in the larger diameter classes, and the lowest in the smaller diameter classes. During the observed period (1983–2022), there was a decline in the number of trees, uncharacteristic changes in the basal area and smaller changes in tree volume. This pattern confirms that the forest is still in an optimal phase, but a comparison of the diameter classes revealed a gradual aging of the stand.
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