Large-scale restoration of species-rich dry grasslands on arable land: environmental filtering drives successful species establishment over a period of 10 years.
Abstract
Sowing of regionally specific seed mixtures on former arable land is increasingly used to restore species-rich grasslands but it often faces important obstacles in environmental conditions and colonisation from preserved surrounding grasslands. Long-term landscape scale studies, which explore the processes governing plant establishment from seed mixtures and later colonisation from the surrounding landscape are scarce. We studied the species and functional trait composition of 32 grasslands restored 1-11 years before the first sampling by sowing regional seed mixtures in the White Carpathian Mts (SE Czech Republic). We compared them with 23 well-preserved permanent grasslands in their surroundings. In each grassland, we estimated plant species cover in three plots of 25 m2, in restored grasslands in 2009, 2014 and 2019, in permanent grasslands in 2009. The species composition of the restored grasslands converged towards the permanent grasslands due to expansion of dry grassland species and retreat of mesic grassland and weed species. The majority (60%-71%) of the vegetation cover of restored grasslands was formed by sown species, while the species number was mainly determined by colonising unsown species (61%-63%). The species number of restored grasslands remained lower than that in permanent grasslands. Functional trait composition (community weighted mean) of the sown seed mixtures, permanent grasslands and restored grasslands overlapped in all three samplings. With increasing grassland age, species with resource-retaining traits of low specific leaf area and high leaf dry matter content, lower stature, higher seed mass and lower capacity for clonal reproduction expanded. Functional trait diversity of the plots was mostly lower than expected by null model randomisations of community, which indicates strong environmental filtering. Comparison of newly colonising species and extinct species indicated that mainly species with traits similar to the rest of the community are able to colonise the grasslands successfully. Synthesis and applications: Sowing of regionally specific seed mixtures was successful and demonstrated to be a fast way of grassland restoration, particularly in terms of functional trait composition. The resulting species diversity depended on the colonisation processes, which are controlled by the functional composition of the local communities.