The importance of human mediation in species establishment : analysis of the alien flora of Estonia

In order to analyse the mechanisms of the crossing of invasion phases by alien species, a comprehensive 787-species database of all alien neophytes ever recorded in the Estonian flora was compiled. The invasiveness (invasive status, abundance type, introduction mode, residence time, etc.) of each species was estimated and analysed. Our analysis shows that humans have played a more profound role in fostering plant naturalisations than by acting simply as dispersers - the percentage of naturalisation among the deliberately introduced species is considerably higher than among the accidentally introduced taxa. Cultivation has preferred long-lived species that have advantages for reaching greater abundance and naturalised status in the area, especially in (semi-)natural communities. Invasion success also increases with alien species residence time in the study area. There is definitely a need, in the future, to regulate introductions, especially to control the ornamental plant trade.