Benchmarking plant diversity of Palaearctic grasslands

Background and Aim: Knowledge on typical levels of plant species richness of plant communities is required both for fundamental research and biodiversity conservation. Vegetation ecologists and practitioners need reference richness values to be able to assess the diversity value of specific plant communities. Palaearctic grasslands, which cover around 22% of the realm surface, are known to host high plant diversity at small spatial scales, some of them being the world record holders. However, there are also some very species-poor Palaearctic grasslands. In any case, maximum and minimum richness values are only a small part of the story. It is evident that for a robust knowledge on plant diversity mean values averaged using many replicates are needed. As plant diversity is strongly dependent on spatial scale, here we aim at providing benchmarks of plant richness values of different Palaearctic grassland types at eight grain sizes: 0.0001 m2, 0.001 m2, 0.01 m2, 0.1 m2, 1 m2, 10 m2, 100 m2 and 1000 m2. Previous studies have already proved that richness of vascular plants, bryophytes and lichens is not congruent across vegetation types, therefore, besides total plant diversity, we aim to assess separately vascular and non-vascular plant diversity, as well as the two components of the latter, bryophytes and lichens. Location: Palaearctic grasslands and low-scrubs. Taxa: Vascular plants, bryophytes and lichens. Methods: We will use data extracted from the GrassPlot database, which stores standardized vegetation-plot data sampled in precisely delimited plots. They make a total of 117,777 plots of the eight standard grain sizes, which will be analysed together with 1,051 additional plots provided specifically for this survey by Milan Chytrý and other colleagues. The 118,828 plots span a wide range of grassland and low scrub types, including rocky, sandy, xeric, meso-xeric, mesic, wet, Mediterranean, and alpine grasslands, as well as heathlands, thorn-scrubs, ruderal communities and azonal grasslands such as dune grasslands, salt marshes, wetlands, and rocks and screes. All these vegetation types are distributed across eight biomes throughout the Palaearctic realm