Alien and native species in Central European urban floras: a quantitative comparison

The paper provides quantitative information on the occurrence of alien species in Central European cities and analyses factors determining the richness of alien and native floras in this habitat type. Data for 54 cities (25 Polish, 24 German, 4 Czech and 1 Austrian) were gathered, and the representation of archaeophytes (i.e. aliens introduced before 1500 ad ), neophytes (introduced after that date) and native species was expressed. In an average city there were 87.4 archaeophytes (15.2% of the city flora) and 172.4 neophytes (25.2%) giving a total of 259.7 for alien species (40.3%). The number of native species averaged 386.5. The numbers of species in each category of immigration status increased significantly with city size. For neophytes, the species-area relationship showed a higher slope (0.49) on log–log axes than for both archaeophytes (0.16) and native species (0.30). Not only the number, but also the relative contribution of neophytes to the total flora, increased with city size, indicating that neophytes are the group which are most closely associated with human activity. On the other hand, archaeophytes were better represented in smaller cities, as they were confined to rural environment. A step-wise multiple regression was used to test for environmental variables acting as significant predictors, and explained between 40 and 65% of variation in the species numbers for particular categories of immigration status, providing the best fit for neophytes. City size was the best predictor for each characteristic, except of the proportion of total aliens, where the percentage of explained variability was low (8.2%), with latitude being the only significant predictor. Temperature was another highly significant predictor for the number of archaeophytes and total aliens, reflecting the origin of aliens in warmer areas. There was an effect of region on some flora characteristics. Polish cities had significantly higher proportion of archaeophytes and of total aliens than German cities. It is concluded that the occurrence of native and alien species in urban floras follows rather different pattern.     

Invasiveness of alien plants in Brussels is related to their phylogenetic similarity to native species

Aim Understanding the processes that drive invasion success of alien species has received considerable attention in current ecological research. From an evolutionary point of view, many studies have shown that the phylogenetic similarity between the invader species and the members of the native community may be an important aspect of invasiveness. In this study, using a coarse‐scale systematic sampling grid of 1 km², we explore whether the occupancy frequency of two groups of alien species, archaeophytes and neophytes, in the urban angiosperm flora of Brussels is influenced by their phylogenetic relatedness to native species. Location The city of Brussels (Belgium). Methods We used ordinary least‐squares regressions and quantile regressions for analysing the relationship between the occupancy frequency of alien species in the sampled grid and their phylogenetic distance to the native species pool. Results Alien species with high occupancy frequency in the sampled grid are, on average, more phylogenetically related to native species than are less frequent aliens, although this relationship is significant only for archaeophytes. In addition, as shown by the quantile regressions, the relationship between phylogenetic relatedness to the native flora and occupancy frequency is much stronger for the most frequent aliens than for rare aliens. Main conclusions Our data suggest that it is unlikely that species with very low phylogenetic relatedness to natives will become successful invaders with very high distribution in the area studied. To the contrary, under future climate warming scenarios, present‐day urban aliens of high occupancy frequency are likely to become successful invaders even outside urban areas.     

Native and alien floras in urban habitats: a comparison across 32 cities of central Europe

Aim To determine relative effects of habitat type, climate and spatial pattern on species richness and composition of native and alien plant assemblages in central European cities. Location Central Europe, Belgium and the Netherlands. Methods The diversity of native and alien flora was analysed in 32 cities. In each city, plant species were recorded in seven 1‐ha plots that represented seven urban habitat types with specific disturbance regimes. Plants were classified into native species, archaeophytes (introduced before ad 1500) and neophytes (introduced later). Two sets of explanatory variables were obtained for each city: climatic data and all‐scale spatial variables generated by analysis of principal coordinates of neighbour matrices. For each group of species, the effect of habitat type, climate and spatial variables on variation in species composition was determined by variation partitioning. Responses of individual plant species to climatic variables were tested using a set of binomial regression models. Effects of climatic variables on the proportion of alien species were determined by linear regression. Results In all cities, 562 native plant species, 188 archaeophytes and 386 neophytes were recorded. Proportions of alien species varied among urban habitats. The proportion of native species decreased with increasing range and mean annual temperature, and increased with increasing precipitation. In contrast, proportions of archaeophytes and neophytes increased with mean annual temperature. However, spatial pattern explained a larger proportion of variation in species composition of the urban flora than climate. Archaeophytes were more uniformly distributed across the studied cities than the native species and neophytes. Urban habitats rich in native species also tended to be rich in archaeophytes and neophytes. Main conclusions Species richness and composition of central European urban floras are significantly affected by urban habitat types, climate and spatial pattern. Native species, archaeophytes and neophytes differ in their response to these factors.     

Effects of different cultivation types on native and alien weed species richness and diversity in Moravia (Czech Republic)

Changes in weed species richness and beta-diversity are partly attributable to different types and intensity of disturbance and partly to broad-scale variation in environmental conditions. We compiled a data set of 434 vegetation plots of weed vegetation in root crop and cereal fields in Moravia (eastern Czech Republic) to compare the effects of environmental conditions and different disturbance regimes on species richness and beta-diversity. To detect changes in species richness, we related the variation in species richness to individual environmental conditions. To assess differences in beta-diversity between the vegetation of cereal and root crop fields, we used Whittaker's measure of beta-diversity. The relative importance of each environmental variable for the variation in species composition was evaluated using canonical correspondence analysis. All analyses were done for all vascular plant species and separately for native species, archaeophytes and neophytes. A comparison of weed vegetation of root crops and cereals showed a distinct dichotomy between these two types of weed vegetation. There was no significant difference in total species richness and native species richness; however, cereal fields were richer in archaeophytes and root crop fields were richer in neophytes. The beta-diversity of weed vegetation was higher in root crops. Environmental factors explained a significant part of the variability in richness of both natives and aliens. The richness of native species increased and beta-diversity decreased with increasing precipitation. The opposite relationship was found for archaeophytes, in both cereals and root crops. These results confirmed the importance of climatic factors and management practices for changes in weed species composition. They also showed a distinct pattern of species richness and beta-diversity of native and alien weed species.     

Native and alien plant species richness in relation to spatial heterogeneity on a regional scale in Germany

Aim The aim of our study was to reveal relationships between richness patterns of native vs. alien plant species and spatial heterogeneity across varying landscape patterns at a regional scale. Location The study was carried out in the administrative district of Dessau (Germany), covering around 4000 km². Methods Data on plant distribution of the German vascular flora available in grid cells covering 5′ longitude and 3′ latitude (c. 32 km²) were divided into three status groups: native plants, archaeophytes (pre 1500 AD aliens) and neophytes (post 1500 AD aliens). Land use and abiotic data layers were intersected with 125 grid cells comprising the selected area. Using novel landscape ecological methods, we calculated 38 indices of landscape composition and configuration for each grid cell. Principal components analysis (PCA) with a set of 29 selected, low correlated landscape indices was followed by multiple linear regression analysis. Results PCA reduced 29 indices to eight principal components (PCs) that explained 80% cumulative variance. Multiple linear regression analysis was highly significant and explained 41% to 60% variance in plant species distribution (adjusted R²) with three significant PCs (tested for spatial autocorrelation) expressing moderate to high disturbance levels and high spatial heterogeneity. Comparing the significance of the PCs for the species groups, native plant species richness is most strongly associated with riverine ecosystems, followed by urban ecosystems, and then small‐scale rural ecosystems. Archaeophyte and neophyte richness are most strongly associated with urban ecosystems, followed by small‐scale rural ecosystems and riverine ecosystems for archaeophytes, and riverine ecosystems and small‐scale rural ecosystems for neophytes. Main conclusions Our overall results suggest that species richness of native and alien plants increases with moderate levels of natural and/or anthropogenic disturbances, coupled with high levels of habitat and structural heterogeneity in urban, riverine, and small‐scale rural ecosystems. Despite differences in the order of relevance of PCs for the three plant groups, we conclude that at the regional scale species richness patterns of native plants as well as alien plants are promoted by similar factors.     

Diversity of native and alien plant species on rubbish dumps: effects of dump age, environmental factors and toxicity

Abstract. The flora of 96 rubbish dumps consisting of organic, inorganic and industrial wastes was studied in the Czech Republic. Some dumps contained toxic substances (heavy metals, chlorethylenes, phenols, polychlorinated biphenyls, oil hydrocarbons and biogas). Statistically significant factors explaining the number and proportional representation of native plant species, archaeophytes (introduced before 1500) and neophytes (introduced later) were determined. In total, 588 species of vascular plants were recorded, with archaeophytes (133 species) over‐represented and native species (322 species) and neophytes (133 species) under‐represented compared to their proportions in the national flora. Minimum adequate models were used to determine the effects of several factors on species numbers and proportions, independent of other factors. Dump area, human density in the region and altitude (non‐significant only in archaeophytes) were correlated positively with species numbers. Dump age, expressed as time since dump establishment, interacted with the dump toxicity; species numbers increased with dump age on non‐toxic dumps, whereas on toxic dumps no increase in numbers was noted. For neophytes, dump toxicity also interacted with human density; the increase in numbers of neophytes with human density is more pronounced on toxic than on non‐toxic dumps. The variables measured failed to explain observed differences in proportional representation of native species, archaeophytes and neophytes. This suggests that the occurrence of species growing in such extreme habitats is driven overwhelmingly by factors such as anthropogenic disturbance. A possible explanation for the positive effect of altitude on species numbers on dumps is that the effect of heating of the deposited substrate by microbiological processes, documented by previous studies, overrides the effect of altitude which was shown repeatedly to have a negative effect on species richness. Neophyte distribution is driven by an interplay of factors distinct from those influencing the distribution of native species, namely toxicity and human density (the latter we interpret as a surrogate for propagule pressure). Their distribution on studied dumps is more restricted than that of native taxa and archaeophytes, and they are more limited by toxic substrata; more intensive propagule pressure is required for their establishment at dumps with higher toxicity levels.     

Diversity of native and alien vascular plant species of dry grasslands in central Europe

Question: Which factors determine diversity of native and alien vascular plant species in semi‐natural dry grasslands? Location: Northern limestone Alps to the southern rim of the Bohemian massif in northern Austria. Methods: In 70 randomly chosen dry grassland patches (0.008 ha ‐ 7 ha) we sampled a complete inventory of vascular plant species at each site. We analysed the correlation between species diversity of natives, archaeophytes (pre‐1500 aliens) and neophytes (post‐1500 aliens). We used GLM to study the relationship of species number (natives, neophytes, archaeophytes) to five explanatory variables (altitude, within habitat diversity, habitat diversity of adjacent areas, within land‐use diversity and land‐use in adjacent areas). Orthogonal components of these variables were derived with a PCA and used in the models. We also tested the influence of minimum residence time (MRT) and the covariables origin, mode of introduction and life form on the number of grassland sites with neophytes with analogous GLMs. Results: Native species diversity species was positively correlated with the species diversity of new, but not old invaders. GLM explains 70% of the variance in the number of native species. Patch size explained the largest part of the variation in the number of native species. PCA axes 1 and 3 were significantly related to the number of native species. Axis 1was related to on‐site habitat and land‐use diversity. The GLM of the archaeophyte diversity explains 18% of the variance. Altitude and presence of fields and grassland in the neighbourhood mainly explained archaeophyte species diversity. The GLM of neophyte diversity explains 12% of the variance. The number of neophytes was positively related to that of archaeophytes. Only PCA axis 3, which is mainly influenced by adjacent land‐use types, showed a relationship with neophytes. MRT, mode of introduction and region of origin (but not life form) were significantly related to the number of grassland sites invaded by neophytes, explaining 35% of the variance. Conclusion: Most factors governing native species diversity are not significantly related to alien species diversity. Additional determinants of the local scale diversity of alien species exist such as region of origin and historical factors (MRT, mode of introduction).     

An updated checklist of the vascular flora alien to Italy

An updated inventory of the vascular flora alien to Italy, providing details on the occurrence at regional level, is presented. The checklist includes 1597 species, subspecies, and hybrids, distributed in 725 genera and 152 families; 2 taxa are lycophytes, 11 ferns and fern allies, 33 gymnosperms, and 1551 angiosperms. 157 taxa are archaeophytes and 1440 neophytes. The alien taxa currently established in Italy are 791 (570 naturalized and 221 invasive), while 705 taxa are casual aliens, 4 are not assessed, 7 are of unknown regional distribution, 47 have not been confirmed in recent times, 3 are considered extinct or possibly extinct in the country, and 40 are doubtfully occurring in Italy. This checklist allows to establish an up-to-date number (9792) of taxa constituting the whole (native and alien) Italian flora.     

Widely distributed native and alien plant species differ in arbuscular mycorrhizal associations and related functional trait interactions

It is debated whether alien plants in new environments benefit from being mycorrhizal and whether widely distributed natives and aliens differ in their associations with mycorrhizal fungi. Here, we compared whether species differing in their origin status, i.e. natives, archaeophytes (alien species introduced before the year 1500) and neophytes (introduced after the year 1500), and arbuscular mycorrhizal (AM) status (obligate, facultative, non‐mycorrhizal) differ in their area of occupancy in Germany (i.e. number of occupied grid cells, each ~130 km²). We used generalized linear models, incorporating main effects and up to three‐way interactions combining AM status, origin status and plant functional traits. The latter were chosen to describe the possible trade‐off in carbon allocation either towards the symbiosis or to other plant structures, such as storage organs (significant interactions involving traits were assumed to indicate the existence of such trade‐offs). AM status significantly explained the area of occupancy of natives and neophytes – with facultative mycorrhizal species occupying the largest area in both groups – but was less pronounced among archaeophytes. Archaeophytes may have reduced dependency on AM fungi, as they are generally agricultural weeds and the symbiosis potentially becomes obsolete for plants growing in habitats providing a steady provision of nutrients. Trait interactions between AM status and other functional traits were almost exclusively detected for neophytes. While facultative mycorrhizal neophytes benefit from trade‐offs with other traits related to high C cost in terms of area of occupancy, such trade‐offs were almost absent among natives. This indicates that natives and neophytes benefit differently from the symbiosis and suggests that native AM fungal partners might be less important for neophytic than for native plant species or that more time is required to establish similar relationships between neophytes and native fungal symbionts.     

Interaction of local and landscape features in the conservation of Hungarian arable weed diversity

Question: How do local and landscape management contribute to weed diversity in Hungarian winter cereal fields? Location: Central Hungary. Methods: Vascular plants were sampled in 18 winter cereal fields along an intensification gradient according to nitrogen fertilization, in the first cereal rows (edge) and in the interior part of the fields. Weed species were divided into groups according to their residence time in Central Europe (native species, archaeophytes, neophytes) and nitrogen preference (low to medium, LMNP, and high, HNP species). The percentage of semi‐natural habitats was calculated in the 500 m radius circle. Effects of fertilizer use, transect position and semi‐natural habitats were estimated by general linear mixed models. Results: We recorded 149 weed species. Fertilizer had a negative impact on the species richness of archaeophytes and LMNP species, and on the cover of native weeds. There was greater species richness and weed cover at the edge of the fields than in the centre. A higher percentage of seminatural habitats around the arable fields resulted in greater total species richness, especially of archaeophytes and LMNP species. We found an interaction between the percentage of semi‐natural habitats and transect position for species richness of archaeophytes and LMNP species. Conclusions: Reduced use of fertilizers and a high percentage of semi‐natural habitats would support native and archaeophyte weed diversity even in winter cereal fields, while large amounts of fertilizer may promote invasion of neophytes. However, the beneficial effect of the semi‐natural habitats and greater species pool on the arable flora may prevail only in the crop edges.