Dry grasslands of Sicily: Multi-taxon diversity and classification challenges

Aims: In Southern Europe, grassland phytosociologists typically do not record non-vascular plant taxa and focus either on annual or perennial vascular plants even when both groups co-occur spatially. By contrast, researchers from temperate and northern Europe typically aim to record the entire community. We thus asked how such a comprehensive sampling approach would affect vegetation classification and biodiversity analyses when applied to Mediterranean dry grasslands. Study area: Island of Sicily, Italy. Methods: We sampled homogeneous stands of dry grasslands of different soil types and from sea level to 1200 m a.s.l. with nested-plot series and additional 10-m2 plots, each with a complete list of all terricolous vascular plant, bryophyte and lichen taxa. For the 67 plots, ten square meters each, we additionally estimated the cover values of the species and determined structural, topographic and soil variables. We subjected these 67 plots to TWINSPAN and determined diagnostic taxa for the clusters at two hierarchical levels. Results: The mean total species richness increased from 2.1 in 0.0001 m2 to 60.6 in 100 m2 with 15% non-vascular plant taxa on average. The four main TWINSPAN clusters corresponded to base-rich coastal sands (mainly Ammophiletea), acidic inland sands (mainly Poetea bulbosae), nutrient-rich loamy soils (mainly Chenopodietea) and alkaline clayish soils (mainly Lygeo-Stipetea). Each cluster contained annual and perennial plants and mostly also non-vascular plant taxa, both in the species com bination and the diagnostic species. Conclusions: Alpha and beta diversity of Mediterranean grasslands is higher than previously thought. While our numerical analyses yielded well characterised and ecologically meaningful units, there was no separation of annual and perennial grassland types at the higher level. We thus recommend recording all vascular plant species occurring in the plot also in Mediterranean regions, so as to allow straightforward comparisons with the rest of Europe in biodiversity studies.