Seed introduction and gap creation facilitate restoration of meadow species richness

Summary owing to traditionally managed grasslands has been considered as a useful restoration tool at sites where local dispersal is limited. A three-year trial in northern Finland sought to answer the following questions: 1) can the species richness of semi-natural grassland be increased with seed sowing, and 2) is the slow increase in species richness under continuous mowing management explained by dispersal and/or micro-site limitation? Seeds of eight grassland herbs were sown into permanent plots with four treatments (no mowing, June mowing, August mowing and soil disturbance). The fate of emerged seedlings was monitored for three seasons. Large differences were found between different species and treatments. Four species produced a notable amount of seedlings. Only two species could establish a permanent population on the site, Dianthus deltoides and Prunella vulgaris. Their establishment rate in plots with August mowing and soil disturbance was around 10%. As much as 82% of all observed seedlings emerged in the soil disturbance treatment. The study supported dispersal as well as micro-site limitation. Dispersal limitation was evidenced by the successful germination of 50% of sown species. The lack of suitable germination sites restricted seedling establishment effectively, as exposing mineral soil enhanced germination greatly. As the traditional management of meadows included July hay cut followed by autumn grazing, gaps were created for seedling establishment, the present results suggest that if grazing animals are not available gaps to sward should be produced by mechanical means. Overall, seed sowing can facilitate restoration of impoverished semi-natural grasslands where the species richness has decreased due to insufficient management and when local seed sources are no longer present.