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Aim: Climate is an important factor controlling plant distributions. However, it is not yet fully understood how climate interacts with human impacts or whether the effects of these factors differ between native and alien species. Facing ongoing climate change and urbanization, we explore the effects of climate on plant species richness and composition across European cities. - Location: Sixty cities in Western, Central and Southern Europe. - Taxon: Vascular plants. - Methods: Species presence was recorded in seven habitats in each city. Large scale climatic gradients were derived from 22 climatic variables using a partial principal component analysis that controlled for the effects of human population size and gross domestic product. The effects of climate and habitat type on the numbers of native and alien species were tested using linear mixed effect models. The native and alien compositional variation across cities and habitats was analysed using principal component analysis with variation partitioning. - Results: The Mediterranean to temperate climatic gradient had a significant effect on species numbers across all habitats. The numbers of both native and alien species increased from the Mediterranean to temperate Europe. Within each city, the proportion of alien species decreased from highly urbanized to less urbanized habitats. Climate had a stronger effect on the composition of alien plants than on the composition of native plants. The native species composition especially changed from the Mediterranean to temperate cities and alien species composition also from oceanic to continental cities. - Main conclusions: Urban native and alien species richness follow the pattern found for the whole European flora. Based on this observation, we suggest that the future shift of warm and dry conditions from the Mediterranean to the north that is expected under global change scenarios could affect richness and change the composition of European urban floras. However, this shift would not necessarily alter the proportions of aliens.

Aim It is generally believed that communities of small organisms, or those with small propagules, are structured mainly by local niche-based processes, and less by dispersal limitation. Conversely, weaker environmental and stronger spatial structure, indicating dispersal limitation, are expected to occur more frequently in communities of large organisms. However, this hypothesis has rarely been tested by comparing spatial and environmental effects across groups of organisms of different size (or with different size of propagules) sampled at the same set of sites. Here, we test it in urban environments. Location Thirty-two cities in 10 countries of Central Europe and Benelux. Methods Wecompared effects of spatial location and climate on species composition of different groups of organisms sampled in corresponding types of urban habitats. The studied groups were: (1) subaerial cyanobacteria and algae, (2) vascular plants, (3) land snails; and subgroups of vascular plants with different life form and dispersal mode, namely: (4) herbs, (5) animal-dispersed trees and shrubs, and (6) wind-dispersed trees and shrubs. Data were analysed by variation partitioning based on redundancy analysis (RDA) with principal coordinates of neighbour matrices (PCNM). Eighteen PCNM eigenvectors (expressing spatial effects) and mean annual temperature, July–January temperature difference and annual precipitation sum (expressing environmental effects) were used as explanatory variables. Results Pure effects of climate on species composition, indicating niche-based processes, were not significant for any group or subgroup of the studied organisms. In contrast, pure effects of space, indicating dispersal limitation, were significant for all groups and subgroups except herbs. Surprisingly, the community of cyanobacteria/algae possessed much stronger spatial structure independent of climate than communities of larger organisms, although cyanobacteria/algae had the lowest beta diversity among the studied cities. Main conclusions We hypothesize that the community of subaerial cyanobacteria/ algae is structured by natural processes which involve dispersal limitation, whereas communities of urban plants and snails are influenced by human-assisted dispersal of their propagules between cities, which results in weaker dispersal limitation. Our study indicates that dispersal vectors can be more important for community structure than size of organisms or of their propagules.

Aim Urbanization is associated with strong changes in biodiversity, but the diversity of plant and animal assemblages varies among urban habitats. We studied effects of urban habitats on the diversity of vascular plants and land snails in 32 large cities. Location Central Europe, Belgium and the Netherlands. Methods The species composition of all vascular plants that had not been planted by humans, and all land snails, was recorded in seven 1-ha plots within each city. Each plot contained one urban habitat type representing a different disturbance regime: historical city square, boulevard, residential area with compact building pattern, residential area with open building pattern, park, early successional and mid-successional site. For each plot, we obtained temperature and precipitation data. The effects of climate and habitat types on species composition were quantified using ordination methods with an adjusted variation partitioning algorithm. Differences in species composition among urban habitats were described using statistically determined diagnostic species, and differences in alpha, beta and gamma diversity were quantified. Results A total of 1196 plant and 87 snail species were recorded. Habitat type explained higher proportions of the total variation in both plant and snail species composition (11.2 and 8.2%, respectively) than did climate (4.6 and 6.3%). For both taxa, the main differences in species composition were observed between strongly urbanized sites in city centres and early successional and mid-successional sites. For vascular plants, the number of species was lowest in city squares and boulevards, and highest at successional sites and in residential areas with compact building patterns. Beta diversity of vascular plants calculated for the same habitat types among cities was highest for squares and successional sites. The number of snail species was lowest in city squares and at early successional sites, and highest at mid-successional sites. The highest beta diversity of snail assemblages among cities was observed within the city square and early successional habitat types, and the lowest within residential area habitat types. Main conclusions Urban habitats differ notably in the diversity of their vascular plant flora and land snail fauna. Understanding the habitat-related biodiversity patterns in urbanized landscapes will allow projections of future impacts of urban land-use changes on the biota.

Aim The diversity changes that occurred in Central European forests during the early Holocene can be better understood using ecological knowledge of modern analogues of these forests, which occur in far Eastern Europe. Here we compare the diversity of vascular plants, bryophytes and snails among different forest types of the Southern Urals to provide insights into the palaeoecology of the vanished Central European forests. Location Southern Ural Mountains, Bashkortostan, Russia. Methods We recorded all species of vascular plants, ground-dwelling bryophytes and land snails, and measured biotic and abiotic variables, in 100-m2 plots located in four forest types dominated by different trees: Pinus sylvestris-Larix sibirica, Betula pendula-Populus tremula, Quercus robur and Acer platanoides-Tilia cordata-Ulmus glabra. These types correspond to the chronosequence of forest communities that occurred in Central Europe in the early Holocene. Results The species richness of herb-layer plants was most affected by the canopy-transmitted light. The former three forest types had open canopy and were rich in species, whereas the Acer-Tilia-Ulmus forests were darker and poor in species. The species richness of ground-dwelling bryophytes decreased from coniferous to broad-leaved deciduous forests. In contrast, the highest species richness of snails was in the Acer-Tilia-Ulmus forests owing to the higher calcium content in the litter of these trees. Main conclusions Based on the modern analogue of the Southern Ural forests, we propose the hypothesis that the late-glacial open-canopy pine and larch forests of Central European lowlands were rich in light-demanding species of vascular plants, many of which were also typical of tall-grass steppes or mesic grasslands. They also contained several species of ground-dwelling bryophytes. The spread of birch, aspen and oak in the early Holocene reduced the local species richness of ground-dwelling bryophytes but not of vascular plants. The subsequent spread of elm, lime, maple and ash caused canopy closure, a retreat of the light-demanding herbs and a decline in the local species richness of vascular plants. Besides the increased shading by these tree species, their litter enriched soils in calcium, and enhanced decomposition and nutrient cycling. This supported an increase in the species richness of land snails.

Aim Shells of fossil molluscs are important for palaeoecological reconstructions. However, habitat requirements of snail species typical of central European full-glacial loess sediments are poorly known because most of them became very rare or extinct in Europe. The recent discovery of an almost complete extant assemblage of such species in mountainous regions of central Asia enables more precise characterization of their habitats, which may significantly improve reconstructions of Pleistocene environments. Location Altai Mountains, Russia. Methods Terrestrial snail assemblages, vegetation composition and selected environmental variables were recorded at 118 sites along a gradient of climatic continentality in the Russian Altai. Habitat characteristics of sites where the species typical of full-glacial period occurred were described using a classification tree. Results Seven of the eight species that are typical of central European full-glacial loess sediments were found in the study area. They were confined to cool areas with January mean temperatures below -17 C, but occurred mainly in sheltered habitats with a warmer microclimate such as scrub or open woodland. Pupilla loessica and Vallonia tenuilabris had the broadest habitat range, occurring from woodland to dry steppe. Unexpectedly, Columella columella, Pupilla alpicola, Vertigo genesii, V. parcedentata and V. pseudosubstriata were mainly found in wooded fens and shrubby tundra rather than in open steppe. Most of these seven species were recorded in base-rich wooded fens. Very dry open steppe habitats usually supported no snails. Main conclusions Habitat ranges of the studied snails in the Altai indicate that the full-glacial landscapes of central European lowlands that harboured these species were not completely dominated by open and dry loess steppe. Most probably they contained a significant component of shrubby vegetation, patches of wet habitats, and probably also areas of woodland at sites with favourable mesoclimate.