Vascular Flora and Plant Communities of the Boston Harbor Islands TED ELLIMAN* Abstract - 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. Introduction The Boston Harbor Islands national park area is part of the Boston Basin Ecoregion of the Northeastern Coastal Zone (Barbour et al. 1998). There are 34 islands within the park, ranging in size from less than 0.1 hectare, or 0.2 acres (Nixes Mate), to 105 hectares, or 259 acres (Worlds End). Many of the islands are drumlins formed through glacial movement and deposition, while others, such as those in Hingham Harbor, are formed of rock outcrops (National Park Service 2000). The primary vegetation of this general region is the glaciated “Oak- Chestnut Forest” of the eastern United States (Braun 1950) or the “Appalachian Oak Forest” (Kuchler 1964). The extent to which the pre-colonial forests on the Harbor Islands resembled the oak-hickory-chestnut-maplebeech- white pine association characteristic of eastern Massachusetts is the subject of a paper in this volume (Patterson and Richburg 2005). Native Americans had cleared much of the Boston area for agriculture by the time of European colonial settlement. Francis Higginson, writing in 1630, stated that there were virtually no trees in the vicinity of Boston, and that wood supplies for the British settlements came from the Harbor Islands (Wessels 1997). *Wilberforce Environmental Associates, 4038 Chaucer Place, Slingerlands, NY 12159. Current address - 95 Westview Road, Voorhheesville, NY 12186; telliman@ nycap.rr.com. Boston Harbor Islands National Park Area: Natural Resources Overview 2005 Northeastern Naturalist 12(Special Issue 3):49–74 50 Northeastern Naturalist Vol. 12, Special Issue 3 All of the islands have a long history of human use, and many have served residential, institutional, and military purposes (Kales and Kales 1983). Some islands continue to be used and occupied. This history of use and occupancy has disrupted the natural communities on the islands. Much of the flora consists of non-native plants, and virtually all of the islands’ upland and freshwater wetland habitats have been impacted by human activities. Many of the Harbor Islands have been botanically surveyed in the past. An Illustrated Flora of the Boston Harbor Islands (Levering 1978) is the most comprehensive survey of the islands’ vascular plants, investigating 21 of the islands and listing a total of 231 species. Other surveys include studies of Bumpkin Island (McLaughlin 1994), Grape Island (Perkins 1985), and several of the outer islands (Hernandez 1976). The US Coast Guard Auxiliary has written a visitors’ guide to the plants of Little Brewster Island (Snowman 1999), and the Metropolitan District Commission has published a partial list of the flora on Peddocks Island (Commonwealth of Massachusetts 1989). In 1984, Bruce Sorrie, former State Botanist, documented rare plants on Langlee, Ragged, and Sarah Islands in Hingham Harbor (field records on file at the Massachusetts Natural Heritage and Endangered Species Program). Hopping (2000) has surveyed and mapped the plant communities of Worlds End. For this project, I inventoried the vascular plant species on 30 of the islands, and surveyed the upland plant communities on 18 islands. Scott LaGreca of Harvard University identified the vascular plants on The Graves and Nixes Mate. Moon and Hangman Islands are the only two islands that were not covered in this survey. The goal of the vascular plant inventory was to cover as many islands and identify as many plants as possible, and to document rare plant occurrences. A second survey goal was to describe, classify, and map the park’s upland plant communities. The survey focused on the park’s upland communities, but freshwater wetland and salt marsh plants are included in the floristic inventory. Methods During the surveys, 32 islands were covered extensively on foot. All of the plant species encountered on each of these islands were identified and recorded. Islands with the largest area and the most botanical diversity were visited repeatedly, while small islands with sparse flora were surveyed once. Plants not identifiable in the field were collected for office identification. Several hundred plant specimens have been collected as vouchers to be maintained at the University of Massachusetts and the Harvard University Herbaria. 2005 T. Elliman 51 The inventory includes all native and non-native plant species in the park that are growing without cultivation. Plants under cultivation and landscaped plants that have not reproduced and become naturalized populations are not included in this inventory. Plant nomenclature follows that used in The Vascular Plants of Massachusetts: A County Checklist (Sorrie and Somers 1999), which is based largely on Kartesz (1994) and initial volumes of the Flora of North America. The locations of rare plant populations identified in the survey were documented with a Trimble GeoExplorer III GPS unit. To classify the park’s plant communities, 134 releve plots (15-meter radius) were sampled in a variety of upland communities on 18 islands. Plots were placed in representative upland habitats selected on the basis of MASS GIS 1:5000 Color Ortho Imagery; aerial photographs (1:12,000 infrared aerial photographs of the national park area, flown in 2000); 1:25,000 USGS topographic maps (Boston South and Hull quadrangles); and personal knowledge of the islands’ upland habitat patterns based on the first year of surveys. For community classification, vegetation structure (the tree, shrub, and herbaceous strata) and dominant species (based on abundance and leaf and stem coverage) within plots were the basis for classifying the park’s upland habitats. Plant community nomenclature follows community classification systems developed by the National Vegetation Classification (Nature- Serve 2001) and by the Massachusetts Natural Heritage and Endangered Species Program (Swain and Kearsley 2000). The widespread presence of non-native plants has confounded the classification of a number of the Harbor Island plant communities. In some cases, community types dominated by non-native species are not described in either the National Vegetation Classification (NVC) or in the Massachusetts classification. Results A total of 521 native and naturalized non-native vascular plant species in 99 plant families were identified for the 32 islands investigated in the survey. Of this total, 229 species (44%) are exotic plants. On many islands, non-native plants account for 50% or more of the species composition. The islands with the largest number of plant species are: Worlds End (301), Peddocks (225), and Thompson (211) (Table 1). These figures are correlated with the size and habitat variety of these large islands. Bumpkin Island (182) and Grape Island (173) also have high species numbers, attributable to habitat diversity and recovering natural communities. Island size is not the only criterion for floristic diversity. The duration and intensity of human uses are influential factors determining the condition and variety of the flora on each of the islands. The history 52 Northeastern Naturalist Vol. 12, Special Issue 3 of plant introductions on many islands has influenced the distributional patterns of naturalized, non-native floristic associations, which may be strikingly different even on adjacent islands with similar habitat conditions (Middle and Outer Brewster, for example). Langlee (110 species) and Ragged (107 species) Islands in Hingham Harbor are small islands with large species numbers relative to their size. In these cases, proximity to the mainland, a sheltered harbor location, a relative lack of disturbance, and persistent species introductions yield a high floristic diversity. The outermost islands (Calf, Great Brewster, Middle Brewster, and Outer Brewster) have fewer species on a per area basis than many islands closer to the mainland. Lack of diversity on these islands is influenced by distance from mainland seed sources and exposure to wind and salt spray, resulting in a slow recovery of habitats from past uses. Staghorn sumac (Rhus hirta (L.) Sudworth1 ) shrublands cover much of Table 1. Floristic inventory results. Area statistics are for the terrestrial component of each island. Island Hectares Acres Total species Exotic species Exotic species % Bumpkin 12.2 30.1 182 92 51% Button 0.2 1.5 42 15 36% Calf 7.5 18.5 90 53 59% Deer 74.9 185.1 52 43 83% Georges 15.8 39.0 93 66 71% Grape 21.9 54.1 172 64 37% Graves 0.1 0.2 1 1 100% Great Brewster 7.5 18.5 108 67 62% Green 1.0 2.5 15 13 87% Langlee 1.8 4.4 110 48 44% Little Brewster 1.3 3.2 39 26 67% Little Calf 0.4 1.0 6 4 67% Long 85.1 210.3 176 85 48% Lovells 19.6 48.4 113 55 49% Middle Brewster 5.0 12.4 40 25 63% Nixes Mate 0.02 0.05 2 2 100% Nut 6.8 16.8 69 42 61% Outer Brewster 7.7 19.0 84 47 56% Peddocks 74.6 184.3 225 114 51% Raccoon 1.3 3.2 85 35 41% Ragged 1.1 2.7 107 39 36% Rainsford 6.6 16.3 103 66 64% Sarah 1.4 3.5 51 20 39% Sheep 0.4 1.0 29 16 55% Slate 4.8 11.9 80 27 34% Snake 2.9 7.2 55 23 42% Spectacle 34.6 85.5 118 60 51% Thompson 54.2 133.9 211 105 50% Webb State Park 13.9 34.3 178 90 51% Worlds End 104.5 258.2 301 101 34% 2005 T. Elliman 53 the upland area on the outer islands, and trees are scarce. Species totals for the largest of the outer islands are: Calf (90), Great Brewster (108), Middle Brewster (40), and Outer Brewster (84). The Graves (one species), Nixes Mate (two species), and Little Calf (three species), which are small outcroppings exposed to overwash from storms and ocean spray, have the fewest plant species. The hectare and acreage figures used in Table 1 cover that part of the islands that are above the high tide mark. This includes all of the terrestrial and freshwater wetland communities on the islands. Acreage of the islands in the Boston Harbor national park area was measured in 2002–03 using vegetation borders to determine this area. On each island, the high tide mark was recorded by walking the uppermost wrack line not in rooted vegetation or the upper edge of the black zone using a geographic positioning system unit (Trimble GeoExplorer III dGPS), creating a polygon for the terrestrial (and freshwater wetland) parts of the islands. Gallops Island, which was largely off-limits and only partially surveyed in this inventory, is not included in Table 1. Rare plants Based on Massachusetts Natural Heritage and Endangered Species Program records and the results of this survey, nine rare plant taxa with a total of 28 plant populations have been reported on 18 of the Boston Harbor Islands since the 19th century. Nineteen rare plant populations were observed and documented in 2001–03 (Table 2), nine of them for the first time. Four rare plant populations documented in the past are most likely extirpated from the park, and the status of five previously Table 2. Rare plant populations documented in this survey. Taxon Islands State Status Angelica lucida (seaside angelica) Calf, Long, Peddocks Watch List (WL) Geranium carolinianum var. confertiflorum (Carolina crane’s-bill) Langlee WL Rumex pallidus (seabeach dock) Bumpkin, Grape, Peddocks Threatened Setaria parviflora (bristly foxtail grass) Georges, Nut Special Concern Solidago speciosa (showy goldenrod) Worlds End WL Suaeda richii (Rich’s sea-blite) Ragged, Thompson WL Tilia americana var. neglecta (coastal basswood) Button, Bumpkin, WL Langlee, Raccoon, Ragged, Sarah, Worlds End 54 Northeastern Naturalist Vol. 12, Special Issue 3 Table 3. Boston Harbor Island plant communities. Massachusetts National vegetation Natural Heritage Provisional name classification equivalent Program equivalent Notes Forests and woodlands Oak-hickory forest Quercus alba (Quercus rubra, carya spp.) Oak-hickory forest Mature, mostly native forest, limited to Worlds End. forest alliance Norway maple forest Dominates sections of Peddocks and Thompson. Mixed maritime forest/woodland Forest or woodland of mixed native and non-native trees. On many islands. Sassafras-hackberry maritime forest Distinctive small forest in Webb State Park. Aspen–gray birch woodland Early successional of mostly native trees: aspens, gray birch, black cherry. Red cedar woodland Juniperus virginiana Maritime juniper Open stands of red cedar on rock outcrops above the woodland alliance woodland/shrubland spray zone. Examples on Langlee, Ragged, Worlds End. Black pine forest Pinus thunbergiana Forest alliance Large stand of black pine (Pinus nigra) on Long Island’s West Head. Shrub communities Maritime shrub community Prunus serotina–Rhus typhina/Cakile Maritime shrubland Community of native and non-native shrubs. On most edulenta shrubland community islands. Dwarf maritime shrub community Maritime shrubland Small staghorn sumac and saltspray rose shrubs, community within spray zone. Field communities Old field community Cultural grasslands Open communities dominated by a mixture of native and non-native grasses and forbs. Little bluestem grassland Small grassland on dry ridge, Grape Island. 2005 T. Elliman 55 Table 3, continued. Massachusetts National vegetation Natural Heritage Provisional name classification equivalent Program equivalent Notes Wetland communities Shrub swamp Cephalanthus occidentalis semi- Shrub swamp Restricted to edges of Ice Pond on Worlds End. permanently flooded shrubland alliance Phragmites marsh Phragmites australis semipermanently Deep emergent marsh Emergent wetland dominated by common reed. flooded rudereal herbaceous vegetation Found on many islands. Cattail–rose mallow marsh Typha angustifolia–Hibiscus moscheutos Deep emergent marsh Outstanding example on Long Island’s West Head. herbaceous vegetation Cattail marsh Typha (angustifolia, latifolia)–Scirpus spp. Deep emergent marsh Narrow-leaf cattail wetland on Middle Brewster. eastern herbaceous vegetation Maritime cliff and beach communities Maritime erosional cliff Maritime erosional cliff Sandy-stony cliffs Mix of herbaceous and scrub vegetation community community on many islands, notably Great Brewster, Peddocks, Thompson. Maritime rock cliff community Steep rock cliffs with native Maritime rock cliff Rock cliffs with little vegetation. On numerous islands. and non-native, sparse vegetation community Maritime dunes Ammophila breviligulata Maritime dune Lovells Island has best example. herbaceous alliance community Beach strand Cakile edulenta sparse Maritime beach strand Most islands have this shoreline community at the high vegetation alliance community tide line. 56 Northeastern Naturalist Vol. 12, Special Issue 3 documented occurrences is uncertain.2 Most of the islands’ rare species are coastal plants limited in distribution to shorelines, coastal marshes, and dunes. Federally listed and globally rare plant species have never been documented in the national park area. The seven rare plant taxa documented in this survey have state rarity designations of “threatened” (one species), “special concern” (one species), and “watch list” (five species). See the Discussion section (below) for a definition and details of these designations. Plant communities Six vegetation categories have been identified for the Boston Harbor Islands national park area: forests (trees dominant, greater than 60% canopy cover), woodlands (trees dominant, less than 60% canopy cover), shrub communities (shrubs dominant), old fields (open habitats with grasses and forbs dominant), freshwater wetlands, and maritime associations (Table 3). The maritime category is to a large extent based on geologic rather than vascular plant features. It includes communities that are close to the shoreline and periodically subject to salt spray and storm flooding. It does not include intertidal habitats, such as salt marshes and mud flats, which are the subject of another survey (Bell et al.. 2005). In the maritime category, only the beach strand community, occurring on beaches just above the high tide line, is based on a distinctive plant association. Plant communities within these categories are typically named for the dominant plant components of the community (Norway maple forest, or red cedar woodland, for example) and/or the physical structure of the community (dwarf maritime shrub community). Discussion Non-native plants The percentage of non-native vascular plant species (44%) documented in the Boston Harbor Islands national park area is high, but it is comparable to percentages reported in other coastal parklands in New York and Massachusetts, with ranges from 35% to 60% of the total flora (Backus et al. 2002, Frankel 1999, Stalter and Lamont 2002, Stalter and Scotto 1999). For the entire state of Massachusetts, non-native species comprise 43% of the flora growing without cultivation (Sorrie and Somers 1999). Non-native plants dominate many of the islands’ upland and freshwater wetland habitats. While many of these species are typical of disturbed habitats throughout Massachusetts, some, such as European ash (Fraxinus excelsior L.), Japanese hops (Humulus japonicus Sieb. & Zucc.), kudzu (Pueraria lobata (Willd.) Ohwi), and tamarisk (Tamarix parviflora DC.) are localized or rare in the state. Centuries 2005 T. Elliman 57 of human impacts and plantings of exotic species that have escaped, persisted, and in many cases proliferated on the islands have contributed to the variety of the Harbor Islands’ naturalized flora. A number of islands have diverse assemblages of exotic trees. Examples include the Siberian elm (Ulmus pumila L.) grove on Middle Brewster; the Norway maple (Acer platanoides L.), English oak (Quercus robur L.), and small-leaved linden (Tilia cordata P. Miller) woodland on Thompson; and the Siberian elm, English oak, European ash, and black cherry (Prunus serotina Ehrh.) woodland on Rainsford Island. East Head on Peddocks Island has large patches of mature, almost monocultural Norway maple forest. Langlee, Ragged, and Sarah Islands have woodlands with the non-native sycamore maple (Acer pseudoplatanus L.), tree-of-heaven (Ailanthus altissima (P. Miller) Swingle), European larch (Larix decidua P. Miller), white mulberry (Morus alba L.), and honey locust (Gleditsia triacanthos L.). Gallops Island has a stand of tamarisk on the beachfront near the landing. The non-native white poplar (Populus alba L.) dominates the northern drumlin of Lovells Island. Japanese barberry (Berberis thunbergii DC.), oriental bittersweet (Celastrus orbiculata Thunb.), Morrow’s honeysuckle (Lonicera morrowii A. Gray), glossy buckthorn (Rhamnus frangula L.), and multiflora rose (Rosa multiflora Thunb. ex Murray) are abundant in the islands’ shrub thickets. Old field communities have many non-native plants, especially members of the composite (Asteraceae), legume (Fabaceae), and grass (Poaceae) families. Mugwort (Artemisia vulgaris L.), goosefoot (Chenopodium album L.), and curly dock (Rumex crispus L.) are rampant in upland old fields throughout the islands. The invasive common reed (Phragmites australis L.) dominates many of the park’s freshwater wetlands. Broad-leaved pepperweed (Lepidium latifolium L.), purple loosestrife (Lythrum salicaria L.), and reed canary grass (Phalaris arundinacea L.) are also invasive in these communities. Native plants Worlds End, three of the small Hingham Harbor Islands (Button, Ragged, Sarah), Grape, and Slate are the only islands with a proportion of native species exceeding 60% of the total flora (Table 1). In the cases of these islands, proximity to the mainland, a relatively sheltered location in or near Hingham Harbor, and less intensive historical impacts are the probable causes of the greater presence of native plants. The Worlds End peninsula has the largest number of native plants, a result of its large size, varied topography, habitat diversity, connection to the mainland, and relative lack of historical disturbance. The mature oak forest on the southeast side of the Worlds End peninsula has a particularly diverse association of native woodland species. 58 Northeastern Naturalist Vol. 12, Special Issue 3 Red cedar woodlands, located on Langlee, Ragged, and Worlds End, and the beach strand communities found throughout the islands also have a high proportion of native plants (see plant community discussion). The most common and widespread native species on the islands include: (trees) gray birch (Betula populifolia Marsh), hackberry (Celtis occidentalis L.), eastern red cedar (Juniperus virginiana L.), big-tooth aspen (Populus grandidentata Michx.), quaking aspen (Populus tremuloides Michaux), and black oak (Quercus velutina Lam.); (shrubs and vines) bayberry (Myrica pensylvanica Loisel.), staghorn sumac, wild red raspberry (Rubus idaeus L.), and poison ivy (Toxicodendron radicans (L.) Kuntze); and (herbaceous plants) common milkweed (Asclepias syriaca L.), hedge bindweed (Calystegia sepium (L.) R. Br.), red fescue (Festuca rubra L.), Canada hawkweed (Hieracium canadense Michaux), and seaside goldenrod (Solidago sempervirens L.). The plant families with the largest number of species on the Harbor Islands are: Asteraceae (composite): 79 species (41 native, 38 non-native) Cyperaceae (sedge): 20 species (19 native, 1 non-native) Fabaceae (legume): 20 species (4 native, 16 non-native) Poaceae (grass): 53 species (28 native, 25 non-native) Rosaceae (rose): 35 species (22 native, 13 non-native) Past and present rare plant occurrences in the park Angelica lucida L. (seaside angelica). Seaside angelica grows in beaches, salt marshes, and rocky shorelines from Labrador to Long Island (Gleason and Cronquist 1991). The three documented Boston Harbor Islands populations occur on the upper edges of brackish marshes on Calf, Long, and Peddocks Islands. Seaside angelica is a watch-list species in Massachusetts. Hernandez (1976) reported this species on Calf and Little Brewster Islands. Aristida tuberculosa Nutt. (seabeach needlegrass). Seabeach needlegrass is a dune species occurring along the Atlantic coast from Massachusetts to Georgia, with inland occurrences at the Great Lakes and on dry uplands in the southeastern United States. Massachusetts populations have been documented in Essex, Middlesex, Plymouth, and Suffolk Counties (Sorrie and Somers 1999). It is a special-concern species in Massachusetts. In 1877, a population was documented on Deer Island by C.E. Faxon. This record is the earliest known documentation of a rare species on the Harbor Islands, and it is the only record of seabeach needlegrass in the park. It is most likely extirpated from Deer Island due to development. Geranium carolinianum L. var. confertiflorum Fern. (Carolina crane’s-bill). Carolina crane’s-bill occurs throughout the contiguous United States. In some areas, the taxon is considered a weed. It has a 2005 T. Elliman 59 wide distribution in Massachusetts, where it is a watch-list species. Var. confertiflorum is distinguished from the nominate variety on the basis of a more compact and crowded inflorescence (Gleason and Cronquist 1991). There is a large population on Langlee Island, where it was first reported by Levering (1978). It was reported on Little Brewster in the 1990s (Snowman 1999), but was not seen in this survey. Rumex pallidus (seabeach dock). Seabeach dock is a maritime species found on beaches from Newfoundland to Long Island, NY. In Massachusetts, where it is classified as a threatened species, it occurs in Essex, Norfolk, Plymouth, and Nantucket Counties. The Boston Harbor Islands' populations grow along the upper tideline where there is little vegetation. In this survey, seabeach dock was found on Bumpkin, Grape, and Peddocks Islands, where the populations have been known for many years. The Bumpkin and Grape Island populations are very small. A population on Thompson Island, consisting of two plants, was reported in 1984, but it has not been seen since then. Setaria parviflora (Poiret) Kerguelen (bristly foxtail)3 . Many of the foxtail grasses (Setaria spp.) are non-native species inhabiting fields and disturbed sites. Bristly foxtail is widespread in the United States, the Caribbean Islands, and South America, where it occurs as far south as Chile (Gandhi and Barkworth 2003). The species reaches its northeastern range limit in southeast Massachusetts, where it is found in fields and salt marshes on Cape Cod, Martha’s Vineyard, Nantucket, and Bristol and Plymouth Counties. This special-concern species is the only native foxtail of the six Setaria species listed for Massachusetts (Sorrie and Somers 1999). Bristly foxtail grass was found on Georges and Nut Islands in this survey. Solidago speciosa Nutt. (showy goldenrod). Showy goldenrod is scattered throughout Massachusetts, where this watch-list species is near its northern range limit (Gleason and Cronquist 1991). The plant favors old fields with a circumneutral substrate. The large Worlds End population, which has been known for many decades, “represents the only extant population in the greater-Boston area” (Hopping 2000). Suaeda species (sea-blites). The Suaeda genus has perplexed a number of botanists. Fernald (1907:140), for example, wrote that the “genus Suaeda has long been for the American botanist a source of much confusion and difficulty.” Sorrie (1987:153) stated: “I believe that a major obstacle in taxonomic revisions of this genus is the reliance on dried material for determinations. Shrinkage and distortion of leaves and sepals make them almost useless for discriminatory work. … Their distinctiveness needs to be worked out in a study of living plants. …” Most of the Suaeda are salt marsh species. The two rare sea-blites that have been reported on the Harbor Islands, American sea-blite 60 Northeastern Naturalist Vol. 12, Special Issue 3 (S. calceoliformis (Hooker) Moq.) and Rich’s sea-blite (S. richii Fern.), range from the maritime provinces of Canada south to Massachusetts and New Jersey. American sea-blite is a special-concern species and Rich’s sea-blite is a watch-list species in Massachusetts. Suaeda calceoliformis4 (American sea-blite). Bruce Sorrie documented 50 mature American sea-blite plants on Langlee Island in August, 1984, noting that this identification needed verification. The shoreline area identified by Sorrie was searched several times in 2001 and 2002, but the sea-blites seen at this location appear to be the common saltmarsh sea-blite (Suaeda maritima (L.) Dumont). Suaeda richii5 (Rich’s sea-blite). Hernandez (1976) listed Rich’s sea-blite on Calf and Great Brewster Islands, and Sorrie documented it on Ragged and Sarah Islands in 1984. In 2003, I located Rich’s sea-blite populations on Ragged and Thompson Islands. Its similarity to Suaeda maritima makes it easy to overlook, and the species is probably present on more islands. Tilia americana L. var. neglecta (Spach) Fosberg6 (coastal basswood). Coastal basswood trees were found on Bumpkin, Button, Langlee, Raccoon, Ragged, Sarah, and Worlds End. Most of the trees grow on the upper edges of rocky shorelines in thickets of native and nonnative trees and shrubs, including sycamore maple, hackberry, eastern red cedar, bayberry, English oak, black oak, and glossy buckthorn. On Raccoon and Langlee Islands, basswood grows in rocky uplands as well as along the shoreline. The Worlds End basswood population is spread widely over the peninsula. It occurs on the margins of shorelines and brackish marshes and on open uplands, where saplings are colonizing old fields (Hopping 2000). Since basswood has been planted on Worlds End, this population may be derived from a mix of native and introduced stock. Coastal basswood occurs in Barnstable, Essex, Norfolk, and Plymouth Counties in Massachusetts. The difficulty with recognizing coastal basswood as a subspecific taxon is its vague morphological distinction from the nominate variety of basswood, Tilia americana L. var. americana. The only feature that may distinguish coastal basswood is slightly greater pubescence on its lower leaf surfaces. In two studies of coastal basswood, Svenson stated that “differences between T. americana, T. heterophylla, and T. neglecta are pretty weak” (1970, p. 341), and “Tilia neglecta has always been a questionable species of Linden. … Due to variability and absence of a “type” with which the name could be correlated, it has remained one of the least tangible species in a taxonomically difficult genus” (1972:469). Morphological and chemical analysis of Tilia specimens collected in the eastern United States support Svenson’s statement (Hardin 1990, Hickok and Amway 1972). While noting some difference in leaf pubes2005 T. Elliman 61 cence between northern and southern specimens, Hickok and Amway concluded: “Although the geographical variation present may warrant the delimitation of taxa of lower rank within the species, the current data indicate that such subdivisions would be of an arbitrary nature” (Hickok and Anway 1972:7). Hardin’s (1990) taxonomic study of Tilia americana concurs with this analysis. Hardin concluded that all of the Tilia in North America belong to a single species, Tilia americana, with four varieties distinguished on the basis of fine differences in leaf and twig pubescence. “Tilia americana var. neglecta” is not recognized as a distinct variety in this study, only mentioned in passing as a “putative introgressant” between Tilia americana var. americana and Tilia americana var. heterophylla. If coastal basswood is to be treated as a subspecific taxon, and morphological characteristics are unreliable in separating it from Tilia americana var. americana, habitat appears to be the rationale for its distinction. The maritime rocky shorelines and wooded dune communities inhabited by coastal basswood are different than the moist, mature inland forests favored by Tilia americana var. americana. Status and management of rare plant populations Showy goldenrod on Worlds End is the only rare plant population noted in this survey that has suffered observable damage from human activities. Most of this population was mowed while in flower in 2001 and 2002. The population recovered in 2003, and The Trustees of Reservations will schedule future mowings to avoid further impacts to this population. The miniscule seabeach dock populations on Bumpkin and Grape Islands are vulnerable to trampling, extreme storm and tidal conditions, and competition with broad-leaved pepperweed. Neither of these seabeach dock populations, observed in 2001 on Bumpkin, and in 2001 and 2002 on Grape, was seen in a follow-up visit to these two islands in 2003. The seaside angelica population on Long Island is at risk from the spread of purple loosestrife, an aggressive invasive plant. This seaside angelica occurrence was the only rare plant population in the park directly threatened by competition from an invasive species. Purple loosestrife in the vicinity of this seaside angelica population should be removed from the marsh. The possibility of increased visitation patterns in the future has the potential of creating conflicts with rare plant populations on several islands, especially the seabeach dock population on Peddocks Island. This population is concentrated on an attractive beach and is exposed to trampling and campfires. (Cliff erosion is also a longterm concern for seabeach dock on Peddocks.) The rare sea-blite 62 Northeastern Naturalist Vol. 12, Special Issue 3 populations identified in the Hingham Harbor Islands could be at risk of trampling if visitation to these small islands increases. In the future, the park’s rare plant populations that are most exposed to human and natural impacts should be monitored on an annual basis by professional park staff or trained volunteers. An immediate conservation priority is to investigate the small, vulnerable seabeach dock populations on Bumpkin and Grape Islands to determine if their apparent disappearance in 2003 is permanent. New searches for this particularly rare species are recommended for other islands with shorelines beneath high bluffs. More secure rare plant populations in the park may be checked at threeto- five year intervals to monitor population trends and changes in habitat conditions. Future planning for the park should avoid facility development and greater public access to sites with rare plant populations. Future searches are recommended for more rare plant populations. Investigations for seabeach needlegrass on dunes and bluffs, for Rich’s sea-blite on shorelines throughout the islands, and for bristly foxtail grass on seawalls and headlands may locate more populations of these species. Searches for previously documented records, including seaside angelica on Middle Brewster, Carolina crane’s-bill on Middle Brewster, and American sea-blite on Langlee, could determine if these populations still exist in the park. Rank and status symbols of rare plants Rare Massachusetts plants have a “status” designation determined by the scientific staff at the Natural Heritage and Endangered Species Program, Massachusetts Division of Fisheries and Wildlife. Status categories are: endangered (E), for the rarest plants; threatened (T), for the next level of rarity; and special concern (SC), for the third level of rarity. Plants with these designations are protected under the Massachusetts Endangered Species Act (M.G.L., c.131A). A fourth category called watch-listed (WL) plants are “species with no legal standing [with respect to the Massachusetts Endangered Species Act] but considered by the state botanist to be sufficiently uncommon to be monitored in the field and studied further for possible listing.…” (Brumback and Mehrhoff et al. 1996). Plant communities The vegetation in many of the national park area’s terrestrial communities is in a state of partial recovery from a long history of use and occupancy. Although non-native plants are a prominent feature of the islands’ vegetation, comprising 50% or more of the flora in many uplands, the process of natural succession could lead to the establishment of more native vegetation associations on many islands. This process is more evident on certain islands (Grape is the best example, see under 2005 T. Elliman 63 “Woodlands”) than on others. Prospects for plant community succession on the outer islands, more exposed to storms and salt spray, are less certain. Staghorn sumac dominates these islands, and there is little indication of a successional trend toward woodland communities. As natural cycles continue, the recovery of soils even on these islands could lead, incrementally, to more diverse associations of native trees, shrubs, and herbaceous plants. Forests Mature forests are limited on the Harbor Islands. Peddocks, Thompson, and Worlds End have the only closed-canopy stands that cover more than one or two hectares. Oak-hickory forest. The oak-hickory forest on the southeastern side of Worlds End is the only plant community in the Boston Harbor Islands national park area dominated by native trees. Black oak, red oak (Quercus rubra L.), and white oak (Quercus alba L.) share canopy dominance. Red maple (Acer rubrum L.), bitternut hickory (Carya cordiformis (Wangenh.) K. Koch), hop hornbeam (Ostrya virginiana (P. Miller) K. Koch), white pine (Pinus strobus L.), and hemlock (Tsuga canadensis (L.) Carr) occur as canopy-associates and in the forest understory. A stand of large black gum trees (Nyssa sylvatica Marshall) grows in a moist section of this forest. Witch hazel (Hamamelis virginiana L.) and highbush cranberry (Viburnum opulus L.) are common shrubs in the oak forest. The community’s herbaceous flora has many native species characteristic of mature oak forests, including wild sarsaparilla (Aralia nudicaulis L.), striped wintergreen (Chimaphila maculata (L.) Pursh), whorled loosestrife (Lysimachia quadrifolia L.), Indian cucumberroot (Medeola virginiana L.), partridge berry (Mitchella repens L.), interrupted fern (Osmunda claytoniana L.), false Solomon’s-seal (Smilacina racemosa (L.) Desf.), carrion-flower (Smilax herbacea L.), bluestemmed goldenrod (Solidago caesia L.), New York fern (Thelypteris noveboracensis (L.) Nieuwl.), and wild oats (Uvularia sessilifolia L.). Norway maple forest. The East Head drumlin on Peddocks Island has the best example of Norway maple forest in the Harbor Islands. Norway maple is dominant on the higher sections of the drumlin. In some areas, this tree forms a virtual monoculture, casting deep shade over an understory consisting of sapling Norway maples.7 In other places, native and non-native trees are associated with Norway maple in the canopy, and shrub growth is dense and diverse. Black pine (Pinus nigra Arnold), Scotch pine (Pinus sylvestris L.), black locust (Robinia pseudoacacia L.), and the native hackberry (Celtis occidentalis L.), white ash (Fraxinus americana L.), and black cherry also occur in the East Head forest. The invasive oriental bittersweet, Japanese barberry, Morrow’s honeysuckle, and multiflora rose are abundant in shrub understories. 64 Northeastern Naturalist Vol. 12, Special Issue 3 Thompson Island has Norway maple stands along the top of the ridge on the island’s west side, and on lower slopes on the east side. The nonnative English oak and small-leaf linden are common in these stands. Mixed maritime forest/woodland. Many islands have small patches of mature forest with a mixed association of native and naturalized non-native trees. Langlee, Raccoon, and Ragged Islands have good examples of this forest community, which includes: Norway maple, sycamore maple, tree-of-heaven, European larch, black cherry, English oak, and black oak. Coastal basswood occurs in shoreline areas on the edges of this community. Rainsford Island has a unique forest mix of English oak, Siberian elm, and European ash growing with the native black cherry. The woodland phase of the mixed maritime forest community is a younger stand with a more open canopy. White poplar and English oak as well as gray birch, native aspens, and black cherry typically occur in this community above a dense growth of shrubs. The central and northern drumlins of Lovells Island have good examples of this woodland community. Hackberry-sassafras maritime forest. Hackberry and sassafras (Sassafras albidum (Nutt.) Nees) are the primary canopy trees in this unique 1.5-hectare (3.7-acre) area of closed-canopy forest on the lower slopes of Webb State Park’s Upper Neck Cove. Black cherry, black oak, and small-leaved linden are associated in the canopy. The stand’s shrub thickets are weedy and impenetrable—Japanese barberry, Japanese honeysuckle (Lonicera japonica Thunb.), Morrow’s honeysuckle, common buckthorn (Rhamnus cathartica L.), multiflora rose, and poison ivy form a wall of growth beneath the canopy. Saplings and seedlings of hackberry and sassafras are present in the stand, but the density of shrubs limits the potential for the regeneration of these native trees. Woodlands Aspen-gray birch woodlands. Early successional woodlands comprised mainly of native trees occur on a number of islands. This community is distinguished from the “mixed maritime woodland” by the greater proportion of native trees. Grape Island, where woodlands are succeeding shrub thickets on much of the island, has the best example of this woodland community. Gray birch, big-tooth aspen, quaking aspen, black cherry, and red cedar growing 4.5 to 10 meters in height form a dispersed canopy over a dense undergrowth of Morrow’s honeysuckle, bayberry, glossy buckthorn, staghorn sumac, wild red raspberry, Bebb’s willow (Salix bebbiana Sarg.), elderberry (Sambucus canadensis L.), and arrow-wood (Viburnum recognitum Fern.). Bumpkin, Peddocks, and Slate Islands have similar woodland associations. 2005 T. Elliman 65 Red cedar woodland. Langlee and Ragged Islands and the Rocky Neck section of Worlds End have small patches of semi-open red cedar stands growing on outcrops above the shoreline. These communities have an unusual plant association with a high percentage of native species. Shrubs include members of the heath family (Ericaceae), including black huckleberry (Gaylussacia baccata (Wangenh.) K. Koch), late lowbush blueberry (Vaccinium angustifolium Aiton), and highbush blueberry (Vaccinium corymbosum L.). Thicket shadbush (Amelanchier canadensis (L.) Medicus) and running shadbush (Amelanchier stolonifera Wiegand) also occur in these red cedar stands. The herbaceous flora in these woodlands includes columbine (Aquilegia canadensis L.), sand sedge (Bulbostylis capillaris (L.) C.B. Clarke), American pennyroyal (Hedeoma pulegioides (L.) Pers.), orange grass (Hypericum gentianoides (L.) B.S.P.), and blue curls (Trichostema dichotomum L.). Poverty grass (Danthonia spicata (L.) Beauv. ex Roemer & J.A. Schultes) and common hairgrass (Deschampsia flexuosa (L.) Trin.) occur on outcrops in these communities. The Massachusetts Natural Heritage and Endangered Species Program classifies this red cedar association as a “Maritime Juniper Woodland/ Shrubland,” a rare (S1) natural community in Massachusetts. Black pine woodland. Black pine woodland covers most of West Head on Long Island. The large pines are impressive, but they are not regenerating. Sycamore maple and quaking aspen are the successional tree species in this disturbed woodland. Poison ivy is rampant on the ground and also climbing trees. This community approximates the “Pinus thunbergiana” Forest Alliance identified by the National Vegetation Classification for coastal Massachusetts, but the pines on Long Island have been identified as Austrian black pine (Pinus nigra) rather than Japanese black pine (Pinus thunbergiana Franco). Shrub communities Maritime shrub community. This community occurs on almost every island in the park except for those that are too small and entirely exposed to salt spray (Hangman, Green, Little Calf). The maritime shrub community has several phases. A common phase, especially on the outer islands, is completely dominated by staghorn sumac, which forms a canopy 3 to 4 meters in height. These stands have few other shrub or herbaceous species. Calf and Sheep Islands have excellent examples of these staghorn sumac “forests.” The thickets on Sarah Island have tall sumacs over an understory of wild red raspberry and pokeweed (Phytolacca americana L.). Other islands have a diverse variant of this shrub community. Staghorn sumac is still dominant, but many other species occur, including: oriental bittersweet, Morrow’s honeysuckle, bayberry, 66 Northeastern Naturalist Vol. 12, Special Issue 3 Virginia creeper (Parthenocissus quinquefolia (L.) Planchon), glossy buckthorn, multiflora rose, bullbrier (Smilax rotundifolia L.), poison ivy, and wild red raspberry. Maritime shrub communities are given a rank of S3 by the Massachusetts Natural Heritage and Endangered Species Program. Dwarf maritime shrub community. This community consists of scattered shrubs, primarily small staghorn sumacs and saltspray rose (Rosa rugosa Thunb.), growing in sandy flats exposed to storm overwash. Peddocks Island has the largest examples of this community in the low, sandy necks between drumlins. Lovells Island, Webb State Park, the west side of Rainsford, and the eastern foot of West Head on Long Island have smaller examples. Herbaceous plants include downy chess (Bromus tectorum L.), red fescue, four o’clocks (Mirabilis nyctaginea (Michx.) MacMillan), Canada bluegrass (Poa compressa L.), sleepy catchfly (Silene antirrhina L.), seaside goldenrod, and common mullein (Verbascum thapsus L.). Old fields Open communities of perennial grasses and forbs are ubiquitous on the Boston Harbor Islands. The largest fields are the meadows on Worlds End, but most of the islands have at least small areas of open, old field uplands. Herbaceous communities occur on rugged, rocky headlands on the outer islands, in sandy flats on Lovells Island, and on reclaimed building sites on Georges and Rainsford Islands and Webb State Park. Without exception, these field communities have a high proportion of non-native plants. Abundant old field species include common mugwort, sweet vernal grass (Anthoxanthum odoratum L.), pigweed, orchard grass (Dactylis glomerata L.), quack grass (Elytrigia repens (L.) Desv. ex B.D. Jackson), Scotch thistle (Onopordum acanthium L.), timothy (Phleum pratense L.), and curly dock. The sandy field on the south side of Lovells has a number of grasses, including bentgrass (Agrostis stolonifera L.), downy chess, red fescue, and Kentucky bluegrass (Poa pratensis L.). Webb State Park’s reclaimed habitats have a diverse grass and forb association, but these also are comprised of primarily non-native taxa, including: redtop grass (Agrostis gigantea L.), common milkweed, bull thistle (Cirsium vulgare (Savi) Tenore), Queen Anne’s lace (Daucus carota L.), quack grass, red fescue, Canada hawkweed, butter and eggs (Linaria vulgaris P. Miller), reed canary grass, tansy (Tanacetum vulgare L.), common mullein, and cow vetch (Vicia cracca L.). Little bluestem field. Grape Island has a small dry field (< 0.25 ha/0.61 acre) at a high point on the west-central part of the island. A largely native association of little bluestem (Schizachyrium scoparium 2005 T. Elliman 67 (Michx.) Nash), spreading dogbane (Apocynum androsaemifolium L.), common milkweed, and early goldenrod (Solidago juncea Aiton) occurs here. Shrub thickets are succeeding onto this small area. Freshwater wetlands Most of the freshwater (palustrine) wetlands in the Boston Harbor Islands national park area are depressional communities less than 0.5 hectare (1.3 acres) in area. The vegetation in these communities is primarily herbaceous, and the habitats may be classified as emergent marshes. The invasive common reed dominates most of the freshwater wetlands in the park. Phragmites marshes are located on Grape, Great Brewster, Long, Lovells, and Thompson Islands and in Webb State Park. Snake Island and Worlds End also have Phragmites-dominated wetlands, but these tidally influenced communities are brackish (Karnauskas 2001). Several freshwater wetlands had standing water when they were surveyed in 2001 and 2002, but most of them were barely moist during these two dry summers. The marsh east of the landing on Grape Island and the “skating pond” marsh on Thompson Island are the most diverse of the Harbor Islands’ freshwater wetlands. The Grape Island marsh has abundant populations of purple loosestrife and broad-leaved pepperweed, as well as Phragmites. Fumitory (Fumaria officinalis L.), a small, delicate nonnative plant, also occurs here. Native plants include American waterhorehound (Lycopus americanus Muhl. ex W. Barton), awl-fruited sedge (Carex stipata Muhl. ex Willd.), northern willow-herb (Epilobium coloratum Biehler), Clayton’s bedstraw (Galium tinctorium (L.) Scop.), tall goldenrod (Solidago altissima L.), and blue vervain (Verbena hastata L.). Two salt marsh species, black grass (Juncus gerardii Loisel) and salt hay (Spartina patens (Aiton) Muhl.), are abundant in this marsh. The skating pond wetland on Thompson was one of the few palustrine communities that had standing water during the 2001 and 2002 field seasons. Common reed is dominant, but a number of other species, including water millet (Echinochloa walteri (Pursh) Heller), little spikerush (Eleocharis acicularis (L.) R. & S.), purple loosestrife, fall panic grass (Panicum dichotomiflorum Michx.), Pennsylvania smartweed (Polygonum pensylvanicum L.), Olney’s three-square (Scirpus americanus Pers.), and saltmarsh bulrush (Scirpus robustus Pursh) have large populations. Two marshes have little or no Phragmites. The larger of these is the marsh (about 0.5 ha/ 1.2 acre) at the base of Long Island’s West Head drumlin. Narrow-leaved cattail (Typha angustifolia L.) and a spectacular stand of swamp rose mallow (Hibiscus palustris L.) dominate the habitat. False nettle (Boehmeria cylindrica (L.) Sw.), water purslane (Ludwigia palustris (L.) Elliott), and cursed crowfoot (Ranunculus sceleratus L.) 68 Northeastern Naturalist Vol. 12, Special Issue 3 also grow in this marsh. The other wetland is a narrow-leaved marsh on the east end of Middle Brewster. Cattail is almost a monoculture in this small (0.25 ha/0.61 acre) community situated in a low basin between rocky headlands. Shrub swamps and forested swamps. The artificial Ice Pond on the northeast side of Worlds End has a dense growth of buttonbush (Cephalanthus occidentalis L.) shrubs on its edges. Winterberry (Ilex verticillata (L.) A. Gray) also occurs here. The north side of Grape Island has a small patch of deeply shaded, moist red maple forest that appears to be transitional between upland and wetland habitat. Wetland or near-wetland species present here include sensitive fern (Onoclea sensibilis L.), cinnamon fern (Osmunda cinnamomea L.), marsh fern (Thelypteris palustris Schott), and highbush blueberry. Maritime communities Cliffs, dunes, and upper shorelines with vascular plants are included in this broad category. Not included are intertidal communities such as salt marshes, mudflats, and tidal pools that were surveyed by the intertidal survey team (Bell et al., this issue). Beach strand. Almost every island has a sandy, pebbly, or stony shoreline with a zonal plant association of herbaceous, salt-tolerant species growing at the upper tideline. Beach strand species include: orache (Atriplex patula L.), sea-rocket, goosefoot, beach-pea (Lathyrus japonicus Willd.), broad-leaved pepperweed, black bindweed (Polygonum convolvulus L.), wild radish (Raphanus raphanistrum L.), curly dock, saltwort (Salsola kali L.), and cocklebur (Xanthium strumarium L.). The rare seabeach dock is a beach strand species. Maritime beach strand communities are given a rank of S3 by the Massachusetts Natural Heritage and Endangered Species Program. Maritime dunes. Lovells Island is the only one of the Harbor Islands with a large area of sand dunes and a large population of beach grass (Ammophila breviligulata Fern.). Most of the dunes are on the island’s southwest side. Long Island’s southeastern shoreline has a small area of dunes and beachgrass. Maritime Dune Communities are ranked as S2 by the Massachusetts Natural Heritage and Endangered Species Program. Maritime erosional cliff communities. Eroding cliffs are a common feature on those islands with steep-sided drumlins. Great Brewster, Long Island, Peddocks, and Thompson have high, sheer cliffs of sand and stone with little vegetation. Plants that occur on cliff faces, such as yarrow (Achillea millefolium L.), common mugwort, downy chess, Canada thistle (Cirsium arvense (L.) Scop.), butter and eggs, Canada bluegrass, and common mullein, tend to be weedy species that are 2005 T. Elliman 69 also found in old fields. Maritime erosional cliff communities are given a rank of S2 by the Massachusetts Natural Heritage and Endangered Species Program. Bases of erosional cliffs are often wet from groundwater seepage, and moisture-tolerant species are frequently found here. Species include: thicket shadbush, Bebb’s willow, field horsetail (Equisetum arvense L.), spotted touch-me-not (Impatiens capensis Meerb.), marsh skullcap (Scutellaria galericulata L.), American germander (Teucrium canadense L.), and coltsfoot (Tussilago farfara L.). Maritime rock cliff communities. The north side of Slate Island has steep slate cliffs with a mixture of native and non-native plants. Columbine and Scotch lovage (Ligusticum scothicum L.) are the most unusual and striking plants here. Other native species on the cliffs include common hairgrass, red fescue, blue toadflax (Nuttallanthus canadensis (L.) D.A. Sutton), and seaside goldenrod. Langlee and Ragged Islands in Hingham Harbor have steep puddingstone cliffs, especially on the south sides of the islands. The cliffs are exposed to salt spray and are almost devoid of vegetation. Maritime cliff communities are given a rank of S2 by the Massachusetts Natural Heritage and Endangered Species Program. Several of the outer islands have high rock cliffs with sparse vegetation. The few plants on these forbidding outcrops are herbaceous, salt-tolerant, non-native perennials growing in soil pockets nourished by gull and cormorant droppings. Species include: common mugwort, black mustard (Brassica nigra (L.) W.D.J. Koch), pigweed, common mallow (Malva neglecta Wallr.), nodding smartweed (Polygonum lapathifolium L.), and curly dock. Rare plant community rankings In Massachusetts, plant communities ranked as S1, S2, and S3 are considered to be rare in the state and are tracked by the Massachusetts Natural Heritage and Endangered Species Program (Swain and Kearsley 2000). S1 communities are the rarest with five or fewer occurrences or little remaining acreage. S2 communities have 6–20 occurrences, and S3 communities have 21–100 occurrences in Massachusetts. Boston Harbor Island plant communities classified as rare in Massachusetts include: maritime juniper woodland/shrubland (S1), maritime dunes (S2), maritime erosional cliffs (S2), maritime rock cliffs (S2), maritime shrub community (S3), and maritime beach strand community (S3). Maritime erosional cliffs, maritime shrub, and maritime beach strand communities are common in Boston Harbor. Most of the shrub and cliff communities are degraded habitats with a high percentage of non-native plants. Beach strand communities are ubiquitous along the uppermost tide lines on islands throughout the park. 70 Northeastern Naturalist Vol. 12, Special Issue 3 Maritime juniper woodland/shrubland communities occur on Langlee, Ragged, and Worlds End. These small patches in the park’s upland landscape have one of the most native plant associations of any of the Harbor Island plant communities. Maritime dunes with stands of beach grass are few in the Harbor Islands, appearing only on Lovells Island and to a lesser extent on Long Island. Maritime rock cliffs occur on Langlee, Outer Brewster, Ragged, and Slate Islands. Only the slate cliffs on the north of Slate Island have much vegetation. Several of the small outer islands are composed entirely of rock cliffs with almost no vascular plants. None of the S1, S2, or S3 communities identified in this survey is threatened by present patterns of use or visitation. Conservation of natural communities in the park Conservation of the park’s native diversity should focus on the maintenance of a mosaic of natural communities and the targeted removal of invasive species in specific habitats. Non-native plants are pervasive throughout all of the park’s upland and freshwater wetland communities, and present a problem for the park’s native biodiversity. Park-wide removal efforts would be financially and logistically impractical. Management of invasive species for the purpose of restoring plant communities should be directed at specific and well-defined areas where rare species and exceptional natural communities are threatened and degraded by their encroachment. An example is the spread of the invasive purple loosestrife (Lythrum salicaria) in a Long Island marsh with a population of the seaside angelica (Angelica lucida), a watch-listed plant. Another example is the dominance of the invasive common reed (Phragmites australis) in the faunally diverse Grape Island marsh. In these cases, removal of the invasive species would protect and restore native diversity. In other cases, particularly in upland areas, the process of natural succession should result in a richer soil base and a healthier community of organisms. Many of the park’s soils and biological communities have been impoverished by centuries of human disturbance. The conversion of these landscapes to unmanaged parkland should lead, through natural succession, to more diverse assemblages of native flora. The disadvantage of manipulating a depleted habitat to maintain it at a specific stage of succession (meadow or shrubland, for example) is that the community—soils and biota as a whole—will remain impoverished and require continual management. The natural recovery of communities, from sumac thickets to mature woodlands on Grape Island, for example, will establish new niches for a greater diversity of organisms, including species now scarce or absent in the park. 2005 T. Elliman 71 With respect to maintaining an upland habitat mosaic of fields, shrublands, and woodlands in the park, the current pattern of Harbor Island management allows for a significant acreage to remain open (examples are the meadows on Thompson and Worlds End; open grounds near facilities on Georges, Long, and Peddocks; picnic and camping areas on Bumpkin and Grape). Shrublands and fields in the outermost islands, exposed to severe maritime conditions, will naturally remain as open or semi-open communities. All of these areas should remain open for the sake of natural diversity as well as for landscape aesthetics. On many islands, however, the process of natural succession towards more wooded communities will heal and restore damaged habitats. That process should continue without habitat manipulation, except for the removal of invasive plants in specific areas where these undesirable species suppress natural community recovery. Acknowledgments There are many people to thank for professional advice, support, observations, housing, and general guidance. I gratefully acknowledge the help of Katherine Abbott, Marc Albert, Tara Boswell, Russ Bowles, Stephen H. Chan, Sheila Colwell, Mike and Mary Ellen Coulter, David DeKing, Deb DiQuinzio, Mary Foley, Alison Hamel-LeBlanc, Russell Hopping, Bruce Jacobson, Beth Johnson, Mandy Karnauskas, Scott LaGreca, Elisabeth Lay, Cheryl Lowe, Adaela McLaughlin, Mark Mello, Pat Morss, Stephanie Neid, Charles Roman, Ryland Rogers, David Szczebak, Nigel Shaw, Ben Sholl, Lesley Sneddon, Sally Snowman, Lois Somers, Sara Stevens, Patricia Swain, and Henry Woolsey. Paul Somers, Botanist for the Massachusetts Natural Heritage and Endangered Species Program, has been especially supportive, patient, and generous with his time. The National Park Service provided funding, technical assistance, and logistical support for this project. Appreciation is also due to the Massachusetts Natural Heritage and Endangered Species Program for guidance and many hours of professional and technical support. Literature Cited Anderson, R. 1999. 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National Park Service. 2000. Boston Harbor Islands: A national park area. Draft general management plan and draft environmental impact statement. Prepared by the Boston Support Office of the Northeast Region, National Park Service. NatureServe. 2001. International classification of ecological communities: Terrestrial vegetation of the United States. Associations within USFS lower New England Section (221A). Report from Biological Conservation Datasystem, Arlington, VA. Perkins, W. 1985. Wildlife listings: Grape Island. Boston Harbor, Boston. Report on file at Massachusetts Natural Heritage and Endangered Species Program, Westborough, MA. Snowman, S. 1999. Plant life found on Little Brewster Island. Boston Light Interpreters Guide. US Coast Guard Auxiliary, Boston, MA. Sorrie, B. 1987. Notes on the rare flora of Massachusetts. Rhodora 89:113–196. Sorrie, B., and P. Somers. 1999. The vascular plants of Masssachusetts: A county checklist. Massachusetts Division of Fisheries and Wildlife, Natural Heritage and Endangered Species Program, Westborough, MA. Stalter, R., and E.E. Lamont. 2002. Vascular flora of the Jamaica Bay Wildlife Refuge, Long Island, New York. Journal of the Torrey Botanical Society 129(4):346–358. Stalter, R., and S. Scotto. 1999. The vascular flora of Ellis Island, New York City, New York. Journal of the Torrey Botanical Society 126 (4):367–375. Svenson, H.K. 1972. Rediscovery of Tilia neglecta Spach. Rhodora 74:469–474. Svenson, H.K. 1970. A linden (Tilia) forest on Cape Cod (with extended notes on Tilia neglecta, Bromus pubescens, and Ribes hirtellum). Rhodora 72:339–350. Swain, P., and J. Kearsley. 2000. Draft classification of the natural communities of Massachusetts. Massachusetts Division of Fisheries and Wildlife, Natural Heritage and Endangered Species Program. Westborough, MA. Wessels, T. 1997. Reading the Forested Landscape: A Natural History of New England. W.W. Norton Co, New York, NY. Wycoff, P.H., and S.L. Webb. 1996. Understory influence of the invasive Norway maple (Acer platanoides). Bulletin of the Torrey Botanical Club 123(3):197–205. Footnotes 1 Rhus typhina L. is a familiar synonym for staghorn sumac. 2 These five concern the Suaeda (sea-blite) genus, a taxonomically difficult group. See Discussion section. 3 Setaria geniculata (Lam.) Beauv. is a synonym for Setaria parviflora. 4 Suaeda americana (Pers.) Fern. is a synonym for Suaeda calceoliformis. 5 Rich’s sea-blite is sometimes classified as a subspecies of Suaeda maritima: S. maritima ssp. richii (Fern.) Bassett & Crompton. 74 Northeastern Naturalist Vol. 12, Special Issue 3 6 Sorrie and Somers (1999) list coastal basswood as Tilia americana var. neglecta, and the common American basswood as Tilia americana var. americana. In older literature, including Svenson’s studies, coastal basswood is sometimes classified as an independent species, Tilia neglecta Spach. 7 Other studies have demonstrated that Norway maple tends to succeed itself and reduce the diversity of forest areas where it has been introduced or invaded (Anderson 1999, Wycoff and Webb 1996). 2005 T. Elliman 75 Photo: Glasswort (Salicornia maritima), Snake Island salt marsh. (Morss photo) Photo: Sycamore maple (Acer pseudoplatanus)in F.L. Olmsted–designed landscape, Worlds End. (Morss photo) 76 Northeastern Naturalist Vol. 12, Special Issue 3 Photo: Lichnologists Elisabeth Lay and Scott LaGreca examine maritime sunburst lichen Xanthoria parietina (L.) Th. Fr. on Middle Brewster Island. (Morss photo) Photo: Blackberries and raspberries are common in shrub thickets; here Rubus sp. fruiting on Outer Brewster Island. (Morss photo)