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 t he 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 befo re 1500AD), 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 incr eased significantly with city size. For neophytes, the species-area re lationship 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, b ut also the relative contribution of neophytes to the total flora, inc reased with city size, indicating that neophytes are the group which a re most closely associated with human activity. On the other hand, arc haeophytes were better represented in smaller cities, as they were con fined to rural environment. A step-wise multiple regression was used t o test for environmental variables acting as significant predictors, a nd explained between 40 and 65% of variation in the species numbers fo r particular categories of immigration status, providing the best fit for neophytes. City size was the best predictor for each characteristi c, except of the proportion of total aliens: where the percentage of e xplained variability was low (8.2%), with latitude being the only sign ificant predictor. Temperature was another highly significant predicto r for the number of archaeophytes and total aliens, reflecting the ori gin of aliens in warmer areas. There was an effect of region on some f lora characteristics. Polish cities had significantly higher proportio n of archaeophytes and of total aliens than German cities. It is concl uded that the occurrence of native and alien species in urban floras f ollows rather different pattern.