How much do we know about distribution and ecology of naturalized and invasive alien plant species? A case study from subtropical southern Brazil

Megadiverse tropical and subtropical countries may be especially at risk from exotic species invasions. However, for these regions, the number of studies on invasive species is low. This paper aims at synthesizing knowledge on the alien herbaceous and shrub flora in the state of Rio Grande do Sul, southern Brazil, considering both presence of alien species in different vegetation types and availability of trait data. Our database is an extensive list of different studies that present vegetation data or species lists in the state. Trait data was gathered from a large number of sources. Only a small portion of alien plants was found with higher frequency in the analyzed studies, some of them species considered to be invasive. However, the data set available for our study clearly is biased towards well-conserved vegetation, and vegetation types that likely contain larger proportions of alien species have been poorly studied. On the basis of the existing data, it is impossible to assess impact of the large majority of the species considered to be invasive. Ordination analysis of alien species described by traits revealed no clear set of traits associated to species that are considered to be invasive, even though some broad patterns became obvious: C4 grasses of African origin, a group that includes several invasive species, were separated from the large majority of species, and very few invasives are among the large group of European forbs. Overall, we conclude that lack of data is a serious impediment to an evaluation of the risk posed by invasive species for the study region.