Calcareous grassland restoration at a coarse quarry waste dump in the Italian Alps

Establishing semi-natural grasslands by using seeds from wild harvesting is an effective method to restore vegetation with high natural value. However, studies implementing this strategy for the revegetation of coarse soils are scarce. In this study, different types of propagation material (green hay, dry hay, and hay-flower from seed stripping) harvested at a species-rich European vegetation typical for calcareous soils (Mesobromion) were used at different sowing densities (range, 450-3000 seeds per m2) to restore a very unfertile soil consisting of coarse wastes from a calcareous quarry. The experiment, organised in a randomised block design with three replicates, was established in 2009, and the species composition and structure were surveyed over five years. The threshold of 70% vegetation cover effective against erosion was achieved within two years after sowing. Neither the type of propagation material nor the sowing density influenced the number of species transferred or the final vegetation cover. However, seed density affected the time of achieving the 70% threshold of plant cover important for erosion control (two or three years after sowing depending on the seed density). Of the seventy-three donor site species, fifty-nine were recorded at least during one year on the restored site (absolute transfer rate of 81%), but only forty-six were recorded in the last year (final transfer rate of 63%). Vegetation development was characterised by loss or decrease of donor site species not well adapted to grow in nutrient-poor soils and increase by species typical for coarse textured soils. The very low soil nitrogen content caused an abundance of nitrogen-fixing species (legumes) compared with that at the donor site. Restoring very coarse calcareous quarry wastes, even without soil improvement, is possible provided the climatic conditions are favourable and seeds of good quality are available.