Re-creating a woodland and heathland on slate waste in Wales

We report on ecological restoration at Penrhyn, Europe's largest slate quarry, which lies adjacent to Snowdonia National Park and a Site of Special Scientific Interest. Broadleaf woodland and heathland were targeted, to provide wildlife corridors to adjacent habitats of high conservation value. Young tree seedlings (six species) of local provenance were planted into slate pockets amended with nutrients (readily available mineral NPK or an organic mix of biosolids and paper sludge with an estimated five-year impact) and water retentive materials (clay overburden or polyacrylamide gel). Applying mineral NPK increased tree basal area by 70% in the first 18 months. The organic mix gave an increase of 130 % in tree basal area, promoted water retention and stimulated nutrient cycling. Both N-fixing tree species and non-fixers responded to fertilization and small-seeded species responded more than large-seeded ones. Tree basal area increased by 50% in the clay treatment compared with trees planted in bare slate ± gel. The transfer during quarrying of heath vegetation with associated peat to a site designated for restoration proved effective in establishing key heathland subshrubs. Bilberry re-sprouted easily from buried shoots whilst heather turf died, but within one year a flush of heather seedlings had germinated from the seedbank in the transferred peat. Three years on, there was complete ground cover of target heathland species, provided that sheep were excluded. Grazing by rabbits was beneficial in reducing grass and increasing heather cover. Where availability of heathland topsoil was limited, heathland brash was applied to clay-covered slate. Germination of heather proved slow and sparse, with no germination of bilberry.