The Foundation manages approximately 400 acres within the “Serengeti” area of Nantucket’s Middle Moors by regular mowing to reduce tall shrubs. The goal of this effort is to restore grassland habitat to this area to benefit rare plants and provide hunting habitat for northern harriers, a rare bird of prey that nests on Nantucket. Mowing initiated in 1998 has been effective at reducing the height of shrubs such as scrub oak and huckleberry. However, these species efficiently re-sprout from root reserves following disturbance and we have observed limited establishment and expansion of grassland-associated species despite our ongoing management.
Upon the completion of a successful research project that indicated a lack of seeds of desired native species in the soil seed bank as a factor limiting recruitment of grasses and wildflowers in response to repeated mowing, we initiated a follow-up project. The goal of this research was to examine the effectiveness of disk harrowing followed by the addition of locally-collected native grass and wildflower seed within the Serengeti area.
This project evaluated the success of three levels of treatment: harrowing, harrowing plus seed addition, and seeding alone, compared to untreated controls. Disc harrowing within a large area stimulated seed bank germination of varied native early-successional species, but confirmed that key grassland dominants were lacking in the soil seed bank, as their recruitment only occurred in plots where seeds were added. Harrowing plus seed addition accelerated the trend toward the desired restoration outcome. Furthermore, we observed unexpected germination of three state listed rare species only within harrowed area, suggesting that harrowing larger blocks can stimulate germination of patchily distributed seeds of rare species adapted for high seed bank longevity. This research suggests that harrowing followed by native seed addition can be a very effective sandplain grassland restoration tool.
We are currently researching the effects of this technique on vegetation, insect, bird and small mammal populations at Head of the Plains and exploring options for implementing larger-scale harrowing within the Serengeti and on other Foundation properties.