Disturbance History Explains Current Compositional and Diversity Patterns of Primary Picea Abies Forest Vegetation

Development of primeval spruce forests is driven by series of mixed severity disturbances. Disturbances and their legacies revealed by dendrochronological methods are shaping recent tree-stand structure. In this paper, we focused on the effect of disturbance history on vascular plant understorey diversity and species composition. Series of 141 plots (1000 m 2 for dendrochronology and 400 m 2 for understorey) randomly placed in primeval stands in the zone of natural montane acidophilous forests dominated by Picea abies in the Western Carpathians was sampled. Dendrochronological, dendrometric and environmental parameters were compared to understorey properties using ordination methods and Bayesian approach or multilevel linear models (GLMM). Both historical disturbances and current tree-stand structure had significant effect on understorey diversity and composition. Interactions among spruce stand properties, Vaccinium myrtillus cover and topsoil chemical properties drive understorey diversity which decrease in time from the last severe disturbance. Period of severe disturbances between 1860–1890 resulted in legacy of current, relatively homogeneous spruce stands with less diverse understorey dominated by bilberry, in contrast to heterogeneous stands (in terms of age and spatial structure) driven by small-scale lower severity disturbances which showed higher understorey diversity. As a consequence, to preserve full understorey variability in the montane spruce forests, disturbances of all magnitudes and spatial extent should be accepted as natural drivers both in the field of nature conservation and close-to-nature forestry