Zoochory on and off: A field experiment for trait-based analysis of establishment success of grassland species

Aims We tested the establishment success of grassland species in the presence or absence of zoochory by livestock and identified the traits associated with successful establishment. Location Hortobagy National Park, Hungary. Methods In six restored species-poor grasslands we established two species-rich 4 m x 4 m source plots per site in 2013. One source plot was managed by extensive cattle grazing ("zoochory on"), the other one was fenced and protected from grazers ("zoochory off"). We monitored the vegetation development in the source plots (2014-2018), and the establishment success of sown species (2016-2018) in adjacent dispersal plots in four, 20-m-long strips per source plot in a total of 960 dispersal plots. We calculated community-weighted means of thirteen plant traits related to regeneration and competitive ability. The effect of grazing, year, distance from source plots, grazing-year and grazing-distance interactions on population and trait dynamics in the source and dispersal plots were analysed with generalized linear mixed-effect models. Results Although grazing reduced the cover and flowering success of sown species in the source plots, the number of successful establishment events was higher in dispersal plots next to grazed source plots. The sown species were the most abundant in plots adjacent to source plots, but occurred at all monitored distances. Zoochory favoured perennial plants with high specific leaf area (SLA), low leaf dry matter content (LDMC), short stature, light seeds, early flowering period, high clonal index and anemochory index. Conclusions We showed that species that can colonize the matrix with and without zoochory have contrasting trait syndromes. In grazing-adapted ecosystems, fencing source populations of target species does not always seem to be a good option. It was a good tool for increasing the cover and flowering success of the sown species in the short run, but it significantly decreased their chance to colonize the surrounding area in the long run.