Establishment of hemiparasitic Rhinanthus spp. in grassland restoration: lessons learned from sowing experiments

Questions What are the factors limiting the establishment of hemiparasitic Rhinanthus spp., ecosystem engineers promoting diversity and stability of communities, in restoration of species-rich meadows? How can these constraints be overcome? Location Czech Republic, Central Europe. Methods Sowing of Rhinanthus seeds in grasslands of different history, biotic and abiotic properties accompanied by a variety of management practices. Followed by consequent monitoring of establishment and population dynamics and synthesis of relevant literature resources. Results Appropriate timing of seed sowing is needed for successful Rhinanthus introduction. Rhinanthus seeds must be sown at latest in November to break their dormancy (valid for Central European populations; might be different e.g. in oceanic regions). Rhinanthus is able to establish a viable population mainly in low- to moderately-productive grasslands with biomass production below 500g center dot DW center dot m(-2). Its establishment is difficult in grasslands of higher productivity due to the effect of competition for light on the seedlings. Rhinanthus requires grasslands with appropriate management including mowing and removal of litter, if it accumulates. Otherwise, the litter layer strongly suppresses seedling establishment. Litter removal can allow establishment even in some productive communities such as stands of Calamagrostis epigejos. However, early mowing (i.e. mowing conducted before ripening of seeds) can lead to a strong decline or even local eradication of the hemiparasitic annuals. Soil conditions on the site of seed origin and the target site can play an important role, as indicated by failures of establishment of Rhinanthus originating from slightly acidic soils on sites with soil pH values around 8. Suitability of a given site for Rhinanthus introduction can be estimated on the basis of its species composition using the Beals index or less formal expert knowledge of local floristic associations of Rhinanthus spp. In the case of suitable conditions, sowing density of 200-500seeds center dot m(-2) should be sufficient for Rhinanthus establishment. Conclusion Mowing or grazing, litter removal, proper timing of sowing, and use of the seeds from local seed sources should considerably increase probability of Rhinanthus successful introduction. However, stochastic events like adverse weather conditions or damage through herbivory make the prediction of introduction success difficult.