Species diversity and community structure of mountain pastures – a case study from Balkan Range
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Background and Questions: A complex land use history of mountain pastures in the Central Balkan leads to structural community dynamics influencing species performance and species richness patterns. How does compositional diversity perform with scale? Which relationships exist between dominant species and the spatial organization of other community elements? Location: Beklemeto region, Central Balkan National Park, above timberline, 1560-1700m altitude. Methods: We established six environmentally similar sampling sites on six hilltops of the ridge. Within each site we sampled one Nardus sticta-rich and one Vaccinium spp.-rich community stands. In each stand, we recorded species cover (%) data in three 4x4m plots and species presence/absence data along 52m long transects of 5x5cm contiguous micro-quadrats. We tested the increase of Nardus– cover as driver of community composition. We calculated diversity indices for each 4x4m plot. As indicators for fine-scale heterogeneity, we estimated the maximum number of realized species combinations (maxNRC) and the maximum compositional diversity (maxCD) for every transect and the plot sizes at which they appear, by computerized merging of consequent 5x5cm quadrats. Results: Dominants were inversely proportional in percentage cover (4x4m plots) and occurring frequencies (5x5cm plots). Diversity at 4×4 m plots was declining with increasing Nardus-cover. Vaccinium-dominated stands clearly showed higher diversity than Nardus-dominated ones according to diversity indices and maxCD. Two communities did not differ significantly in maxNRC, when dominants were excluded. MaxCD and maxNRC appeared at similar range of plot sizes in both community types. Conclusion: Compositional diversity between communities can be attributed to the biotic effect of matrix species, given that the effect of abiotic constrains and species pool were kept quasi-constant within pair of community stands and across all sampling sites.