Effects of organic fertilisation on seed rain and short-term recruitment of Natura 2000-characteristic plant species in moderately species-rich and moderately species-poor mountain meadows

Following management extensification of meadows, the expected increase of plant species richness strongly depends on propagule availability from seed rain of new species and on their recruitment. Recruitment success therefore depends on the availability of seeds from adjacent areas and suitable microsites for establishment. At the end of a seven-year field experiment conducted in mountain meadows in South Tyrol (Italy), we investigated seed rain and short-term recruitment (seedling emergence and short-term survival) of three model species ( Centaurea pseudophrygia , Danthonia decumbens and Trifolium montanum ) characteristic of Natura 2000 meadows and missing in the aboveground vegetation. We applied three different manure types (MT; slurry, farmyard manure and a combined use of farmyard manure and manure effluent) combined with a nutrient input (NI) gradient from 0 to 1.3 livestock units ha −1 year −1, in moderately species-poor (C1) and moderately species-rich (C2) meadow classes (MC). We hypothesised that increasing NI, regardless of MT, increases seed rain but reduces short-term recruitment success, more strongly in C2 than in C1. Sixteen of the 23 seed rain-related variables we examined were affected either by NI alone (11 variables) or by the interaction of NI and MC (5 variables). NI increased most species richness and seed density-related variables affected by the treatments. Only Ellenberg L and the stress strategy index in C2 decreased with increasing NI. Furthermore, the recruitment was species-specific and decreased with increasing NI. Our study provides evidence that, in absence of natural seed rain, the active introduction of target species is necessary to increase species richness.