Insect-pollinated plants are first to disappear from overgrowing grasslands: Implications for restoring functional ecosystems

Loss and fragmentation of natural and seminatural grasslands threaten the persistence of numerous species and the associated interactions. Awareness of possible biotic filters generated by overgrowth of grasslands, and related shifts in functional trait composition are crucial for restoring ecosystem functions. Yet, changes in the patterns of pollination -related plant functional traits in response to changes in local land use have been largely overlooked. We explored shifts in the functional trait composition and diversity of herbaceous plants in 28 paired sites of open and overgrown seminatural grasslands in Western Estonia, Northern Europe. We tested whether patterns of pollination -related functional traits were associated with the stage of succession (open vs overgrown grassland sites), accounting for the effects of the geographic location of sites and the phylogenetic relationships among species. The successional overgrowth of grasslands caused a significant decline in species richness of herbaceous grassland plants and resulted in substantial changes in the functional composition of plant communities. Grassland species retained in overgrown sites were less likely to be (i) insect -pollinated, (ii) reproducing by seed and (iii) shorter -lived than species in open grasslands. The observed pattern has significant implications for restoring functional grassland ecosystems. As insectpollinated plant species are first to disappear during grassland overgrowth, the consequences for the ecosystem pollination function may be substantial. Moreover, a relatively fast and effective restoration of the pollination function in grassland ecosystems may be achievable only before a significant loss of insect -pollinated species, as insect -pollinated species have been shown to recover more slowly than other plants.