Nantucket’s sandplain grassland and coastal heathland plant communities are globally rare and support many regionally rare and endangered plant and animal species. On Nantucket, many areas of grassland and heathland have been overgrown with scrub oak shrubland or pitch pine forests, or have been lost to development. In order to retain grasslands and heathlands in the island landscape, land managers have used brush-cutting, grazing, and prescribed fire.
These methods have also been used with the goal of converting some areas of dense shrubs such as scrub oak and huckleberry back to earlier successional grassland and heathland. After observing that these species efficiently re-sprout from root reserves following disturbance with limited establishment and expansion of grassland-associated species, we decided to examine the soil seed bank (seeds stored in the soil) to determine if it was a limiting factor.
We collected soil cores from sites in sandplain grassland, coastal heathland, and scrub oak shrubland habitats and grew them out in the Foundation's research greenhouse. A total of 3,548 individual seedlings germinated, which we transplanted and grew to maturity for identification. We found that there were indeed large differences in the seed bank of the three communities. Grassland samples had by far the highest germination, while heathlands had moderate germination and scrub oak shrubland samples had low germination. Grassland and heathland samples had the highest number and diversity of grass and wildflower species, while the scrub oak shrubland samples were lacking most of these.
From this research, we concluded that since key grass and wildflower species that are characteristic of sandplain grasslands were missing from the scrub oak shrubland seed bank, management combining disturbance (such as disc-harrowing) with seed addition of desired grasses and forbs, would most likely speed conversion of scrub oak barrens toward sandplain grassland and coastal heathland habitats. This management technique was tested in a follow-up research project undertaken in the Serengeti area of the Middle Moors.