Plant diversity, species turnover and shifts in functional traits in coastal dune vegetation: Results from permanent plots over a 52-year period

Question: What is the relationship between plant diversity and species turnover in coastal dune vegetation plots? How is the long-term change in species composition of vegetation plots related to shifts in functional traits, and what does it tell us about the dominant processes? Location: Coastal dunes, the Netherlands. Methods: Our data set comprised 52 years of vegetation data from 35 permanent plots in grassland/scrub/woodland vegetation. Vegetation dynamics were described in terms of changes in species composition and abundance, and shifts in 13 functional traits related to resources capture and forage quality, regeneration and dispersal. Results: Species turnover in the plots was high, because of local extinction and colonization. Species-rich plots were more stable in terms of species abundance and composition compared with species-poor plots. Over time, the plots converged with respect to their abiotic conditions, as reflected by Ellenberg indicator values – indicating that the prevailing process was succession. The high species turnover reflected high invasibility: accordingly, the relative importance of annuals increased. Most newcomer annuals, however, were competitive generalists of little conservation value. The functional trait analysis allowed us to unravel the complexity of effects of disturbances and succession, and yielded information on the processes driving the observed vegetation dynamics. Conclusions: In this study, small-scale species turnover was negatively related to species diversity, indicating more stability in species-rich communities. Regarding shifts in trait diversity, unifying filters appeared to be more dominant than diversifying filters. Counteracting this homogenization process poses a challenge for nature management