Impact of plant invasions on functional diversity in the vegetation of Central Europe

Questions: How is the loss of plant species richness, associated with invasions, related to changes in functional diversity? What is the relationship between the traits of invasive species and those of invaded communities? Location: Different Central European vegetation types within the Czech Republic. Methods: Functional diversity was calculated for 260-paired releves, half non-invaded and half invaded by one of 13 widespread invasive species in Central Europe. Four traits (height, SLA, seed mass and clonal index) were considered as a way to understand the functional space occupied by native and alien species in the data set (410 species altogether). Results: Some of the functional diversity (FD) indices used (mean trait dissimilarity, mean nearest neighbour dissimilarity and SD of the mean nearest neighbour dissimilarity) revealed higher trait diversity for the invaded vegetation and negative relationship with species richness, while functional richness and evenness gave higher values for the uninvaded vegetation and positive relationship with species richness. Adding hypothetically the invader into the FD calculations for the uninvaded vegetation was found to increase most of the FD indices used, while excluding it from the FD calculations of the invaded vegetation decreased functional richness and also mean trait dissimilarity. Conclusions: Results suggest that invading aliens tend to be functionally different from native species and are therefore likely to occupy an empty niche in the invaded vegetation. Similarly, the resident species in the non-invaded communities are not likely to occupy the whole potential niche space, which could remain available for the invasive species with different traits. This study suggests that the probability of a successful invasion is related to functional dissimilarities between the alien invader and native species of the resident communities.