Dense white-tailed deer populations represent one of the largest natural disturbance factors on Nantucket, which hosts the highest density of white-tailed deer in Massachusetts (~45-55 deer per square mile). Research, particularly in forested areas, indicates that browse by white-tailed deer can have intense and long-lasting impacts on native vegetation communities, drastically reducing the abundance and diversity of native flowering plants. Our Science and Stewardship Department is researching how white-tail deer might be impacting vegetation composition and diversity within managed sandplain grassland and heathland habitats on Nantucket.
In 2011, an initial research project used a 10-foot fence to exclude deer from a 50 x 50-meter study area on the Foundation’s Sanford Farm property and examined vegetation communities within the exclosure and outside of the exclosure in an adjacent 50 x 50-meter study area. We sampled vegetation community composition for five years and saw very little difference between the area with deer browse and the area without deer browse. The lack of a shift in vegetation composition may be due to the relatively short length of time that deer were excluded, but could also potentially be the result of a depauperate seedbank that lacks seed of the desirable flowering plants we expected to recruit into the exclosure.
As a next step in this project, in 2019 we began a research project designed to examine deer browse pressure on specific flowering native plants, orange milkweed and New England Blazing Star, by adding seed to plots inside and outside of the established deer browse exclosure. If the existing seed bank is lacking seed of these desirable plants, and seed does not arrive on its own, then seed addition of key species may be necessary in future restoration projects. Understanding how deer browse pressure might influence establishment from seed addition may be an important factor in future restoration success. In 2022, we will be growing seedlings of the target species in our greenhouse and planting seedlings in the fall of 2022 or spring of 2021 with the intention of accelerating the establishment of orange milkweed and New England Blazing Star to be able to examine deer browse impacts sooner and assess establishment success of transplants rather than direct seeding. Plants grown in a nursery often reach maturity more quickly than direct seeded plants due to regular watering and more moderate conditions, and our direct-seeded plots were affected by drought and high temperatures which impeded germination and growth in 2019-2022.
We selected Sanford Farm for this research because of the abundance of deer activity observed in the area, the presence of several rare plant species palatable to deer, the lack of public vehicle access (decreasing the potential for vandalism of the exclosure fencing), and the opportunity for increased educational opportunities about our research efforts. The results of this work are relevant to sandplain grassland and heathland communities at this site, Head of the Plains, and many other Foundation-owned properties.