Temporal niche separation of the alien flora of Rome (Italy).

This paper deals with the flowering patterns of alien and native species of the urban flora of Rome. Our hypothesis is that beside their confinement in space, i.e. to very disturbed habitats, several aliens also show a segregation in time, by flowering during and/or after the summer vegetative or blossoming break of most local species. Data from the database of the flora of Italy, from a phenology survey in the city centre and from a field survey of the late-flowering flora of the whole city are presented. The results suggest that the role played by alien species in the flora of the city has a consistent seasonal variation, being more significant in summer and autumn than in spring. A possible explanation for this trend may be that some alien species occupy available temporal-niches unexploited by native species, thus avoiding competition with local Mediterranean plants.