Aims Understanding fine‐grain diversity patterns across large spatial extents is fundamental for macroecological research and biodiversity conservation. Using the GrassPlot database, we provide benchmarks of fine‐grain richness values of Palaearctic open habitats for vascular plants, bryophytes, lichens and complete vegetation (i.e., the sum of the former three groups). Location Palaearctic biogeographic realm. Methods We used 126,524 plots of eight standard grain sizes from the GrassPlot database: 0.0001, 0.001, 0.01, 0.1, 1, 10, 100 and 1,000 m2 and calculated the mean richness and standard deviations, as well as maximum, minimum, median, and first and third quartiles for each combination of grain size, taxonomic group, biome, region, vegetation type and phytosociological class. Results Patterns of plant diversity in vegetation types and biomes differ across grain sizes and taxonomic groups. Overall, secondary (mostly semi‐natural) grasslands and natural grasslands are the richest vegetation type. The open‐access file ”GrassPlot Diversity Benchmarks” and the web tool “GrassPlot Diversity Explorer” are now available online (https://edgg.org/databases/GrasslandDiversityExplorer) and provide more insights into species richness patterns in the Palaearctic open habitats. Conclusions The GrassPlot Diversity Benchmarks provide high‐quality data on species richness in open habitat types across the Palaearctic. These benchmark data can be used in vegetation ecology, macroecology, biodiversity conservation and data quality checking. While the amount of data in the underlying GrassPlot database and their spatial coverage are smaller than in other extensive vegetation‐plot databases, species recordings in GrassPlot are on average more complete, making it a valuable complementary data source in macroecology.

Aim Species–area relationships (SARs) are among the best investigated patterns in ecology, yet the shape of the function that should describe SARs and the biological meaning of the function parameters are disputed. Elevational gradients offer the opportunity of investigating how biodiversity responds to large variations in environmental characteristics within small geographical areas. We asked which function describes SARs at different elevations and explored how variations in environmental characteristics influence SAR shape. Location Alborz Mountains (Iran). Taxon Vascular plants. Methods We used sets of nested plots (0.001 to 100 m2) placed at 100 m intervals from 2,000 to 4,500 m elevation to construct series of nested SARs as species accumulation curves. Then, we used these curves to assess the appropriateness of different SAR functions at different elevations. We investigated how parameters of the power function varied along the elevational gradient in response to variation in environmental parameters (ruggedness, temperature, precipitation, exposed rock, percentages of soil sand and total nitrogen, and productivity, expressed by the normalized difference vegetation index). Results The most frequently observed best fit model was the power function, which is controlled by two parameters: z (the velocity in species accumulation with sampled area) and c (the species richness per unit area). z was positively influenced by temperature and soil nitrogen, decreasing with elevation. c was positively influenced by temperature and soil nitrogen, and negatively by rock cover, decreasing with elevation. Main conclusions The decrease in c‐values with elevation is consistent with the altitudinal decrease in species richness and is explained by the increase in bare rock. By contrast, c was positively influenced by temperature and total nitrogen, which are two factors promoting plant growth. Similarly, z‐values decreased with elevation, thus indicating a decrease in beta diversity.

Climate and environmental heterogeneity are currently discussed as the most important drivers of plant diversity along altitudinal gradients. Compared to functional diversity, taxonomic diversity has received much more attention in research on altitudinal gradients, although functional diversity may provide more information on the ecological mechanisms shaping plant diversity. We assessed the importance of climatic and environmental heterogeneity as drivers of functional diversity in relation to altitude in the central Alborz Mountains, Iran. We sampled 132 vegetation plots along two altitudinal transects. Plant traits including life history, growth form, stem‐leaf ratio, spinescence, hairiness, leaf consistency, dispersal type and plant height were recorded. Functional diversity was measured as functional richness, Rao's quadratic entropy, and their standardized effect sizes (SESs). In general, functional diversity decreased with altitude. The decrease in observed functional diversity was related to the decrease in taxonomic richness. SESs of functional diversity showed contrasting trends, depending on transect and index. At both transects, climatic stress best explained the variation in observed and expected functional diversity. Harsh climatic conditions at higher altitudes decreased the number of species and thus the functional trait space. Environmental heterogeneity played only a minor role for shaping functional diversity. We expect this effect to be due to the length of the sampled altitudinal transects. With increasing length, small‐scale drivers become less effective. The two transects favoured different environmental drivers, meaning that transferability of single studies could be difficult.

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