Returning Sheep to the Island of Nantucket
Background
The Island of Nantucket is home to the sandplain ecosystem, one of the rarest ecosystems in the world. The coastal areas of Cape Cod and Long Island, and including Block Island, the Elizabeth Islands, Martha's Vineyard, and Nantucket have historically hosted large contiguous areas of this community. However, the coastal sandplain habitat has been all but eliminated on Cape Cod and Long Island. It is estimated that over 90% of the remaining sandplain habitat in the world is located on the islands of Nantucket, Martha's Vineyard and Tuckernuck. This habitat supports one of the highest concentrations of rare and endangered species in the Commonwealth. Therefore, protecting and restoring these grasslands is a top conservation goal on Nantucket.
While natural and human-induced fire is believed to have been a common historical occurrence, the direct impact of Europeans and their grazing animals was the most important force that shaped the island’s unique grassland and heathland habitats. Nantucket was one of the largest whaling capitals in the world during the 1700’s and early 1800’s, and a large number of settlers that came to the island during this period brought sheep and other grazing animals with them. By 1845, it was estimated that there were over 15,000 sheep grazing on the island. The sheep overgrazed trees and shrubs, allowing low-growing heathland and grassland plants to develop without competition for sunlight and nutrients. The sandy, nutrient-poor quality of the soils and constant maritime salt spray influence were environmental factors that also contributed to the development of these rare and unique vegetation communities.
Today, maintenance of the remaining grasslands and heathlands on Nantucket necessitates human intervention. Currently, management efforts being implemented by the island’s conservation interests are limited to prescribed burning and brushcutting. The Nantucket Conservation Foundation and its conservation partners are currently utilizing both of these forms of management on their properties and conducting associated vegetation monitoring projects aimed at documenting their effects. However, the land use practice that was predominantly responsible for the development of these communities has not been investigated as a potential management technique. The reintroduction of sheep grazing to control the expansion of woody species is a historically-accurate conservation tool. In addition to the consumption of above-ground plant material, sheep disturb the roots and soil with their hooves, creating ideal sites for the germination of grassland-associated species. These effects, along with variations in grazing patterns over time, are hard to reproduce with brushcutting and/or prescribed burning treatments.
Project History
During the summer of 2005, we initiated a pilot research project aimed at assessing the effectiveness of sheep grazing as a management tool for reducing woody shrub cover, comparing and contrasting the effects of this treatment with mowing, and evaluating the feasibility of employing sheep grazing as a vegetation management tool on a large scale basis. Field work for this project has focused on: (1) designating graze, mow, or untreated management units; (2) establishing and monitoring permanent vegetation plots within these units to document pre-treatment and post-treatment vegetation characteristics; (3) conducting two mowing and grazing treatments on a rotational basis; and (4) data analysis.
Plans for Future Research
Data from this research will be used to develop a habitat management plan that will benefit not only the Foundation’s land management efforts, but those being conducted by our conservation partners as well. Furthermore, this project aims to address issues of environmental conservation and historical preservation. By serving as a link between these interests, sheep have promoted opportunities for collaboration between different organizations for the purposes of education. For example, field trips with students from Nantucket’s local schools have visited our sheep at Squam Farm and learned about the conservation efforts on the island and how these tie into its unique historic land uses.
In conclusion, preliminary results indicate that both grazing and mowing management methods have advantages and disadvantages. Grazing appears to be better for encouraging the development of vegetation gaps and bare ground, while mowing seems to control woody plant species more effectively. However, our initial results need to be interpreted with caution, as it is difficult to distinguish between the effects of the two treatments being examined and the extremely dry summer that was experienced. In addition, until we see what species become established in the vegetation gaps and the effect that soil disturbance has on the vegetation composition of the area, we will not completely understand the full potential of sheep grazing as a management technique for promoting a heterogeneous and diverse grassland landscape on Nantucket.