Mowing machinery and migratory sheep herds are complementary dispersal vectors for grassland species

Aim We assessed the role of mowing machinery and endozoochory by migratory sheep as dispersal vectors in semi-natural grasslands by comparing the species compositions and traits of species found in the vectors to the regional above-ground vegetation and soil seed bank. Furthermore, we discuss how their interplay may affect the conservation of semi-natural grasslands. Location Rhon Mountains, central Europe. Methods Plant material from mowers (n = 12 from one date) and dung samples from migratory sheep (n = 39 from 13 dates) were collected and the dispersed plant species were determined using the emergence method. We compared the species compositions to the regional above-ground vegetation and seed bank using non-metric multidimensional scaling (NMDS) and indicator species analysis. Furthermore, we compared functional traits of the dispersed species to traits of non-dispersed species of the regional species pools by calculating log-response ratios and performing metaregressions. Results While 43 species were shared between the vectors, the vegetation compositions differed from each other. Mower samples were more similar to the above-ground vegetation whereas dung samples were more similar to the seed bank. Mowers and sheep endozoochory favoured the dispersal of species with different traits and phenologies. Species with small seed sizes were prevalent in both vectors. Mowers were less selective concerning most traits, but favoured high-growing grasses such as Alopecurus pratensis and Trisetum flavescens. Sheep dung samples contained less grasses and more palatable species, such as Urtica dioica. Mowers were most selective concerning phenology, whereas endozoochory by migratory sheep also included late-flowering species. Conclusion Sheep endozoochory and mowing machinery are complementary dispersal vectors favouring species with differing functional traits. Sheep endozoochory enables dispersal of species that have unfavourable traits (e.g. low releasing heights) or phenologies for dispersal by mowing machinery. To ensure the dispersal of a high number of plant species in semi-natural grasslands, the interplay of different vectors should be considered.