Influence of light conditions on variability and diversity of field-layer vegetation in the mountain spruce natural forests | Vplyv svetelných podmienok na variabilitu a diverzitu prízemnej vegetácie prírodných horských smrečín

At five localities of the mountain Norway spruce natural forests in the Nízke Tatry Mts. (Western Carpathians), we studied the effect of light under the forest canopy on the variability and diversity of ground vegetation. Data on vegetation, the availability of light (hemispherical photographs) and other selected environmental factors we obtained for the 302 plots on the size of 1 square m, located in the rectangular grids within individual localities. Chronosequency sampling design of microsite plots allows to study the variability of vegetation on the level of small-scale forest dynamics (gap dynamics). Significant influence of diffuse light on the overall understorey vegetation gradation and herb layer species diversity was found. Strongest positive correlation was found between the diffuse light and the dominance of Athyrium distentifolium and Calamagrostis villosa, but some species more closely correlated with direct solar radiation (Rubus idaeus, Calamagrostis arundinacea). Those species follow canopy gaps and their gradation can be considered as an indication of the decay stage (in terms of the developmental stages of the virgin- forest life-cycle). Slightly negative or indiferent relationship of moss layer and some herbs to the direct solar radiation can be attributed to their occurrence under the shading of high understory vegetation. This effect cannot be recorded by method of hemispheric photographs. Negative relationship between the variables of light availability and tree regeneration (Picea abies) can be explained by the competitive effects of vigorous vegetation, which culminates within larger canopy gaps. This is confirmed by many authors describing the importance of dead wood as an optimal microhabitat for regeneration of trees in the mountain forest conditions. Significant influence of light on the variability of vegetation was also confirmed by direct ordination method CCA, with respect to other important environmental factors. The results of microcoenosis types were statistically tested using one-way analysis of variance and Duncans multiple range test. The species response curves of selected ground vegetation species to the gradient of light (the ecological amplitudes in the short gradient), applicable for the subalpine spruce forests, is also part of this paper.