Cyclic changes in tree species composition of mixed-species forest in Western Carpathians: role of disturbance and tree regeneration

The paper presents results acquired by an analysis of stand structure, regeneration processes and disturbance regime of a mixed natural forest located in the Carpathians (Central Slovakia). The data were collected on two permanent research plots located on different geological bedrocks (andesite and migmatites). Significant differences in the composition of the upper tree layer were observed among two types of geological bedrock. On the plot I (andesite), European ash (Fraxinus excelsior L.) occurred as a dominant component. An opposite situation was observed on the plot II (migmatites). The coexistence of beech (Fagus sylvatica L., spruce (Picea abies L. Karst.) and ash was recorded in the upper layer. The middle and lower layers were almost identical on both types of bedrock. The dominance of beech with the admixture of other tree species was observed. Regarding the structure of the present forest stand in relation to the structure of the gapmakers and natural regeneration, we observed a partial cyclical alternation of the tree species composition of this natural forest within the time span of several developmental cycles. The analysis of natural regeneration implied a crucial role of ungulates for the growth enforcement of ash individuals in the next generation of natural forest. Under the current condition, a negative trend in tree species diversity of the future generation of natural forest towards the dominance of beech was found.