Harrowing and Seed Addition for Sandplain Grassland and Heathland Restoration

Sandplain grassland and coastal heathland are globally rare communities threatened by succession, development, and shoreline change. Restricted mainly to coastal plains of the Northeast. they provide vital habitat for many state and regionally rare species, highlighting their importance for conservation and restoration. Brush-cutting and prescribed lire have been successful in maintaining these communities but have proven ineffective in converting overgrown shrubland to an earlier successional state. Previous research has established that the soil seed bank in overgrown shrubland lacks key dominant grassland species, and that while small-scale soil disturbance leads to short-term increases in grasses and forbs, woody species rapidly resume dominance. We examined whether applying larger-scale soil disturbance in an area previously treated with annual brush-cutting could more effectively impede woody regrowth while providing an extensive mineral soil seed bed to recruit desired vegetation. We evaluated the effectiveness of harrowing, harrowing plus seeding, and seeding alone, compared to untreated plots and to existing sandplain grassland and coastal heathland reference sites. Harrowing stimulated seed bank germination of varied native disturbance-associated species. including four Massachusetts state-listed rare species that recruited only within the harrowed area, and indicated that the seed bank lacked key grassland dominants. Comparison to reference grassland and heathland sites suggested that harrowing plus seeding more closely approached the desired restoration outcome than any other treatment. Our results suggest that larger-scale soil disturbance can enhance biodiversity by stimulating germination of native early successional plants from the seed bank while providing germination sites for sown target species.