|Turtureanu, PD; Palpurina, S; Becker, T; Dolnik, C; Ruprecht, E; Sutcliffe, LME; Szabó, A; Dengler, J: Scale- and taxon-dependent biodiversity patterns of dry grassland vegetation in Transylvania (Romania), Agriculture, Ecosystems and Environment, 182, 15-24 (2014), doi:10.1016/j.agee.2013.10.028|
Patterns of biodiversity may vary across spatial scales and between taxonomic groups; therefore, specific studies are needed to provide insights into factors driving community structure. Semi-natural grasslands are among the most biodiverse ecosystems, providing a suitable model for examining key ecological mechanisms. We analysed dry grasslands in Transylvania (Romania), which harbor extraordinarily species-rich plant communities, including the global maxima for two small grain sizes. We sampled data of vascular plants, bryophytes, and lichens in both nested and separate plots. We used soil, topographic, climatic, and land-use variables as predictors. Species richness at seven grain sizes (0.0001–100 m²) was modeled as a function of these predictors by generalized linear models, followed by multimodel inference over all possible variable combinations with AICc. We also fitted power-law species-area relationships (SARs), both across the full range and for each transition of two subsequent plot sizes, as they provide a way of assessing β-diversity (through z-values) and its dependence on environmental variables. We found large differences in factors between scales and taxonomic groups, which generally supports the hypothesis that niche-related variables are important at very fine scales, while heterogeneity and disturbance-associated parameters become influential at larger scales. We explained the differences among the responses of taxonomic groups by their ecology. The exponents of the power-law SARs (z) for total richness were higher than in most other European dry grasslands, demonstrating that β-diversity is also extraordinary here. Further, the z-values showed strong and unexpected scale dependence, peaking at 0.01–0.1 m², and exponentially decreasing above these grain sizes. In conclusion, our study highlights the strong scale dependence of diversity-environment relationships, both in the case of α- and β-diversity, while emphasizing the importance to study multiple taxonomic groups.