Indigenous and alien vascular plant species in a northern European urban setting (Tallinn, Estonia)

摘要

In recent decades ecologists have accorded special attention to urban areas as loci for the introduction and possible invasion of alien species. Data are lacking on urban flora that would allow having an overview of these phenomena in the Baltic Sea region including in all Scandinavia. This study seeks to address this missing information by establishing the species composition of indigenous and spontaneous alien vascular plants on the territory of Tallinn city, Estonia, and comparing the presence of alien species in the citya€?s greenery-rich areas with their presence more generally in Tallinn. In order to accomplish this, vegetation inventories were conducted on 10 greenery-rich 1 km?2 quadrants in the city and then a database of vascular plant species in Tallinn was compiled using these data together with those from other studies. Inventory data analysed using non-metric multidimensional ordination and permutation tests produced a comparison of indigenous to alien species for the whole of Tallinn. A greenery-rich city, with some tracts having areas of tens of hectares of broad compact forest and semi-natural meadows, Tallinna€?s green areas account for more than one-third (35%) of its entire territory. The analysis showed that the ratio of indigenous plant species to total species in Tallinna€?s greenery-rich areas was significantly higher than that for the whole of Tallinn. These green areas offer valuable habitats for the growth of indigenous species; they are centres of biodiversity and act as buffers for the urban areas by presenting obstacles to the distribution of alien species. The current situation of Tallinn with its high proportion of green areas that contribute to the dominance of indigenous species in its flora should be maintained and valued.