Historical accounts and descriptions of the Boston Harbor Islands were searched for references to the islands' vegetation. They indicate dramatic changes in vegetation structure and composition since 1600. Many of the islands were wooded prior to European settlement, although Native American use is evident before 1600. Forests were cleared for agriculture, building materials, and firewood. Through the centuries since European settlement, the islands have variously supported municipal and military facilities, some of which have since been abandoned. As use of the islands changed, the vegetation of the islands also changed; in some cases native trees and other species returned to abandoned areas, while in others new, exotic species became established or were planted. By the end of the 20^th century the vegetation had become a mixture of woodlands (roughly 25% of the islands as a whole), shrub thickets, open lands, and manicured landscapes, all of which include a large component of non-native species.

We used microfossils preserved in salt-marsh peat to understand the landscape processes (both natural and anthropogenic) that have influenced the environment. Variations in the abundance of fossil pollen of native species suggest that the vegetation of this small, exposed island has been dominated by low, shrubby vegetation since before the arrival of Europeans in the early 1600s. Increases in non-native species since that time may reflect disturbance of the soil associated with grazing and other activities. Sorrel (Rumex) pollen, which indicates local grazing, declines by the late 19^th century, whereas Chenopodiaceae/Amaranthaceae pollen, an indicator of disturbed soil, is most abundant since 1900. Charcoal abundance shows that fires, probably ignited by humans both before and after 1600 A.D., have burned on the island throughout the last 1000 years. In addition, increases in soot and opaque spherules in sediments reflect increased air pollution during the last 100 years. Our analyses provide benchmarks for modern management by documenting pre-European conditions as well as the extent to which the modern environment differs from that prior to the settlement of Massachusetts Bay by Europeans.

From 2001 to 2003, 32 islands in the Boston Harbor Islands national park area were surveyed and inventoried for vascular plant species and plant communities. To date, 521 species in 99 plant families have been identified on these islands. A total of 229 species (44%) are exotic plants. On many islands, non-native plants account for 50% or more of the total flora. The islands with the largest number of plant species are: Worlds End (301), Peddocks (225), and Thompson (211). Duration and type of human uses are influential factors determining the present condition of the flora in the park. Seven rare plant taxa listed as endangered, threatened, special concern, or watch-list by the Massachusetts Natural Heritage and Endangered Species Program were documented on the Harbor Islands in this survey.

Upland vegetation communities on 18 islands have been surveyed, classified, and mapped. Plant communities found on the Harbor Islands include native and non-native forests and woodlands, maritime shrub communities, old fields, beach strand communities, maritime cliff communities, and dune systems.

A survey of the Boston Harbor Islands national park area yielded 175 lichen species in 67 genera, and 70 bryophyte species in 44 genera. Ten percent of the lichens represent a maritime floristic element, and 4% represent a coastal plain element. Caloplaca verruculifera, an orange lichen of rocky shores, is reported new for Massachusetts. Human disturbance and air pollution seem to be the major factors limiting the colonization of lichens and bryophytes on the islands, and specific recommendations for protecting sensitive lichen and bryophyte communities are presented.

Fourteen islands within the Boston Harbor Islands national park area were surveyed for Lepidoptera, Odonata, and tiger beetles (Coleoptera: Carabidae: Cicindelinae) on 67 nights during 2001 and 2002 as part of a five-year inventory of the natural resources of the park. A total of 394 macrolepidopteran species and 166 microlepidopteran species were documented nocturnally, and 51 species of butterflies, 10 of odonates, and 1 tiger beetle were observed during the daytime. Two moths listed in the Massachusetts Endangered Species Act were documented: Spartiniphaga inops (Grote) (Lepidoptera: Noctuidae: Amphipyrinae) and Abagrotis nefascia (J.B. Smith) (Noctuidae: Noctuinae). S. inops is resident on Worlds End, and A. nefascia on Lovells Island. Although two grassland-affiliated genera, Apamea Ochsenheimer (Noctuidae: Amphipyrinae) and Leucania Ochsenheimer (Noctuidae: Hadeninae), were well represented (13 and 8 species, respectively), the total number of macrolepidopteran species was low given the sampling effort and variety of habitats surveyed. Ambient light from Boston and surrounding cites as well as the high percentage of non-native vegetation on many of the islands are two possible factors, in addition to island biogeographic effects, resulting in reduced diversity.

We surveyed birds during May and June, 2001–2003, on 26 islands and 1 mainland location in Boston Harbor, MA. We detected 136 species, 67 of which were suspected of breeding. Abundant breeding seabirds included Double-crested Cormorants (Phalacrocorax auritus), Herring Gulls (Larus argentatus), and Great Black-backed Gulls (Larus marinus). We found 73 Common Eider (Somateria mollissima) nests on Calf, Green, Middle Brewster, and Outer Brewster Islands in 2003, making Boston Harbor one of the largest, southernmost nesting areas for this species on the western Atlantic Ocean. We surveyed 7 wading bird colonies composed of Black-crowned Night-Heron (Nycticorax nycticorax), Great Egret (Ardea alba), Snowy Egret (Egretta thula), Glossy Ibis (Plegadis falcinellus), and Little Blue Heron (Egretta caerulea). We found a colony of Least Terns (Sterna antillarum), a state-listed species, on Rainsford Island. We estimated that 49 species of landbirds nested on Boston Harbor islands, but most islands had few species (mean = 9.8 [± 2.2 (SE)] species per island), presumably because many islands were small and dominated by non-native second-growth forests. The most widespread species were Yellow Warbler (Dendroica petechia), Song Sparrow (Melospiza melodia), and Red-winged Blackbird (Agelaius phoeniceus). We also detected over 50 species of migratory birds which did not nest on islands in the Harbor, including many species of shorebirds and warblers.

The intertidal zone of the 34 islands that are the Boston Harbor Islands national park area encompasses over half of the total park area, thereby representing a significant natural resource. The purpose of this study was to inventory the intertidal zone by classifying and mapping all habitats and compiling species lists for major taxonomic groups. The Boston Harbor Intertidal Classification System was developed for mapping substrate and biotic assemblage types—a system specific to the local area, but capable of application throughout the Gulf of Maine. Intertidal habitats were mapped from GPS-based field delineations. Mixed coarse, consisting of rocks, boulders, cobbles, gravel, shell, and sand, was by far the most common substrate type; however, the islands were variable with a total of 13 discrete substrate types mapped, ranging from bedrock and boulders to mud. The outer islands (e.g., Outer and Little Brewster) were dominated by rocky substrate, while islands close to the mainland (e.g., Thompson, Slate) had high percentages of fine sediments. Of the 31 biotic assemblages mapped, Mytilus edulis (blue mussel) reef was the dominant assemblage on many of the middle and Hingham Bay islands, while the outer islands had assemblages common to the more exposed rocky substrates. The species inventory recorded 95 species of invertebrates, 70 marine algae, and 15 vascular plants. The information generated from this inventory will provide a foundation for natural resource management decisions, design of a long-term intertidal monitoring program, and identification of research needs.

Visitor carrying capacity has been a long-standing issue in management of parks and protected areas. Contemporary carrying capacity frameworks rely on formulation of indicators and standards of quality to define and manage carrying capacity. This paper describes a program of research to support management of carrying capacity of the Boston Harbor Islands national park area, a recent addition to the national park system. Research included: (1) an inventory and analysis of recreation-related resource impacts on selected islands, and (2) surveys of visitors to islands open to public use. Study findings are being incorporated into a visitor carrying capacity management plan through formulation of indicators and standards of quality for the park's natural resources and visitor experience.