Vascular Flora and Plant Communities of the
Boston Harbor Islands
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.
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@
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
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.
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.
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
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.
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
(seaside angelica) Calf, Long, Peddocks Watch List (WL)
Geranium carolinianum var. confertiflorum
(Carolina crane’s-bill) Langlee WL
(seabeach dock) Bumpkin, Grape, Peddocks Threatened
(bristly foxtail grass) Georges, Nut Special Concern
(showy goldenrod) Worlds End WL
(Rich’s sea-blite) Ragged, Thompson WL
Tilia americana var. neglecta
(coastal basswood) Button, Bumpkin, WL
Ragged, Sarah, Worlds End
54 Northeastern Naturalist Vol. 12, Special Issue 3
Table 3. Boston Harbor Island plant communities.
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.
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
Black pine forest Pinus thunbergiana Forest alliance Large stand of black pine (Pinus nigra) on Long
Island’s West Head.
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.
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.
National vegetation Natural Heritage
Provisional name classification equivalent Program equivalent Notes
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.
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,
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.
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 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).
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
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
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
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).
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
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
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
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.
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).
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
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.).
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
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.
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
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
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
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
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
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
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.
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.
Anderson, R. 1999. Disturbance as a factor in the distribution of sugar maple
and the invasion of Norway maple into a modified woodland. Rhodora
Backus, R.H., P.T. Polloni, B.L. Reid, P. Somers, and T.O. Hendrickson. 2002.
The flora of Penikese Island, Massachusetts: The fifth survey (1998–1999)
with emphasis on the woody vegetation. Rhodora 104:219–252.
Barbour, H., T. Simmons, P. Swain, and H. Woolsey. 1998. Our Irreplaceable
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Conservancy, Boston, MA.
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W.D. Countryman and C.B. Hellquist. 1996. Flora Conservanda: New England.
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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)