Determining the significant plant resources and associate desired conditions for the
Boston Harbor Islands national park area.
Carolyn G. Mahan, PhD
Associate Professor of Biology and Environmental Studies
The Pennsylvania State University
209 Hawthorn Building
Altoona, PA 16601
814-949-5530
cgm2@psu.edu
September 2006
Introduction
The Boston Harbor Islands National Park Area (BHI) is a unique NPS unit consisting of
34 islands and peninsulas that vary in size and ecological complexity. A General
Management Plan for BHI was completed in 2002 and recent efforts to inventory the
park’s natural communities were highlighted in 2005 in a special edition of the journal,
Northeastern Naturalist.
In a first step to managing the natural communities of BHI, the significant plant resources
and associated desired conditions and management recommendations needed to be
elucidated. To that end, a one-day workshop was held on Thompson Island on 22 August
2006. Seventeen ecologists, botanists, and natural resource managers (collectively called
ecologists) participated, to some degree, in the workshop. Participants represented state,
federal, and non-profit organizations (Table 1). Prior to the workshop, an agenda was
formulated and shared with all participants (Table 2).
Methods and Results
Based on prior review of published literature and unpublished reports (Richburg and
Patterson 2005, Patterson et al. 2005, Elliman 2005, NPS 2002, BHI Planning Committee
2004) and through facilitated discussion at the workshop, 20 intrinsically significant plant
resources were identified for BHI (Table 3). These significant resources built upon
previous significance statements that had been generated through the park’s General
Management Plan (GMP) and related opinion (NPS 2002, Wilson 2005). These previous
significance statements as they relate to natural resources include:
[BHI contains] islands and peninsulas composed of 1600 acres of land and
wildlife habitats and 35 miles of undeveloped shoreline close to urban area.
[BHI contains] complex natural communities adapted to coastal and island life.
BHI are a natural laboratory......for research and education in biodiversity.
BHI is an ideal place to conduct all-species inventories and to test the concept of
microwilderness.
The significant resources identified at the workshop ranged from locally-rare populations
of plants (e.g., Seabeach Dock) to regionally-significant occurrences of island plant
communities (e.g., exemplary freshwater marsh on Long Island). Rationale for the
significance and some threats to resources were also identified at the workshop (Table 3).
In order to formulate the desired conditions and associated management
recommendations, plant resources for three groups of BHI islands were considered. The
three groups were: Large Islands (Thompson, Moon, Spectacle, Long, Peddocks,
Rainsford, Gallops, Georges, Lovells, Snake, Deer), Hingham Bay Islands (Nut, Sheep,
Raccoon, Grape, Webb State Park, Slate, Bumpkin, Worlds End, Ragged, Langlee, Sarah,
Button), and Brewster Islands (Great Brewster, Little Brewster, Shag Rocks, Middle
Brewster, Outer Brewster, Calf, Little Calf, Green, Graves). Different ecologists were
assigned to each group based on their level of expertise and personal preference.
Participating ecologists prepared 18 desired condition statements and 28 associated
management recommendations for significant resources (Table 4).
Discussion
As a whole, participating ecologists agreed that managing the less diverse, more exposed
Brewster Islands would be less complicated than managing the more ecologically-diverse
and human altered Large Islands and Hingham Bay Islands. In addition, ecologists
agreed with the opinion first articulated by Patterson and his colleagues (2005) that
“change has been a constant park of these landscapes, and that only a lack of change
could be considered to be truly unnatural”(Patterson et al. 2005). Furthermore, this
change has historically and recently been mediated by natural and anthropogenic
processes (Richburg and Patterson 2005).
Natural and anthropogenic processes that historically and recently affected the islands
include climate, fire, overwash, wind, wave action, salt spray, livestock grazing, land
clearing, and the intentional and unintentional introduction of non-natives species. In
general, participating ecologists urged that natural processes predominate on the islands
but, where appropriate, anthropogenic management should be used to achieve a desired
condition (Table 4). In addition, because the presence of invasive, non-native species is a
pervasive problem on all islands, non-native plant removal should be targeted in specific
plant community types and/or in specific locations within BHI. These removals should
not, however, cause a large-scale alteration in the structural integrity of the wide-spread,
maritime-shrub community which provides critical habitat for migrating songbirds. In
some cases, the removal of anthropogenic influences on plant communities may include
allowing the deterioration, or the active removal, of structures, ditches, and barriers
(Table 4).
Finally, all participating ecologists were interested in establishing an island or several
islands where a whole-island restoration could be attempted. This restoration would
require removing most or all non-native species from the island and ensuring that only
native communities and processes occur on the island. Potential candidates for such a
project would be Langlee, Slate, Grape Island, or one of the Brewster Islands.
Table 1. Participants in Boston Harbor Islands national park area plant workshop, August 2006.
NAME
Marc Albert
TITLE
Natural Resource
Specialist
ORGANIZATION
NPS –
BOHA/SAIR/Northeast
Region
EMAIL
Marc_Albert@nps.gov
PHONE
(617) 223-8637
Taber Allison
Vice President
Conservation
MA Audubon
tallison@massaudubon.org
(781) 259-2145
Sheila Colwell
NPS – BOHA/Northeast
Region
Sheila_Colwell@nps.gov
(617) 223-8566
Alison Dibble
Senior Natural
Resource Program
Manager
Botanist
Independent
adibble@earthlink.net
(207) 359-4659
Ted Elliman
Botanist
New England Wildflower
Society
telliman@newfs.org
(518) 225-1815
180 Hemmenway Road
Framingham, MA 01701-2699
Mary Foley
Regional Chief
Scientist
NPS – Northeast Region
Mary_Foley@nps.gov
(617) 223-5024
Nancy Grilk
Boston Harbor Islands
Partnership Planning
Committee
Superintendent
City of Boston; Office of
Environmental and Energy
Services
NPS - BOHA
Nancy.grilk@ci.boston.ma.us
(617) 635-3425
Resource Stewardship & Science
Boston Office NER
15 State St.
Boston, MA 02109-3502
One City Hall Plaza
Boston, MA 02201
Bruce_Jacobson@nps.gov
(617) 223-8669
Ecology Program
Director
Associate Professor of
Biology &
Environmental Science
MA Department of
Conservation & Recreation
Penn St.
Jack.Lash@state.ma.us
(508) 792-7716
x609
(814) 949-5530
Bruce Jacobson
Jack Lash
Carolyn Mahan
cgm2@psu.edu
ADDRESS
Boston Harbor Islands national park
area
408 Atlantic Ave., Suite 228
Boston, MA 02110
Conservation Science & Ecological
Management
Massachusetts Audubon
208 South Great Road
Lincoln, MA 01773
Boston Harbor Islands
408 Atlantic Ave., Suite 228
Boston, MA 02110
Boston Harbor Islands national park
area
408 Atlantic Ave., Suite 228
Boston, MA 02110
180 Beaman St.
W. Boylston, MA 01583
Penn State
209 Hawthorn Building
Altoona, PA 16601
Table 1. (Cont.)
Karen O’Donnell
Friends of the Boston
Harbor Islands
karen-ibew1@excite.com
(781) 891-1326
P.O. Box 540218
Waltham, MA 02454-0218
Jennifer Foreman
Orth
Boston Harbor Islands
Partnership Planning
Committee
Invasive Plant
Ecologist
UMASS Boston
Jennifer.forman@umb.edu
617-287-6490
or 508-405-0883
Bill Patterson
Professor
UMASS-Amherst
wap@forwild.umass.edu
(413) 545-1970
Julie Richburg
Western Regional
Ecologist
The Trustees of
Reservations
jrichburg@ttor.org
(413) 298-3239
x3011
Stephen Smith
Plant Ecologist
NPS - CACO
Stephen_M_Smith@nps.gov
(508) 487-3262
x104
Patricia Swain
Community Ecologist
MA Natural Heritage &
Endangered Species
Program
Pat.Swain@state.ma.us
(508) 792-7270
x160
Andy Walsh
Southeast Regional
Ecologist
The Trustees of
Reservations
awalsh@ttor.org
(781) 784-0567
x7011
Department of Biology
UMASS Boston
100 Morrissey Blvd.
Boston, MA 01701
University of Massachusetts
Department of Forestry & Wildlife
Management
Holdsworth Hall
Amherst, MA 01003
The Trustees of Reservations
1 Sergeant St.
P.O. Box 792
Stockbridge, MA 01262-0792
Cape Cod National Seashore
99 Marconi Site Rd.
Wellfleet, MA 02667
Natural Heritage & Endangered
Species Program
Massachusetts Division of Fisheries &
Wildlife
1 Rabbit Hill Road
Westborough, MA 01581
The Trustees of Reservations
The Eleanor Cabot Bradley Estate
2468B Washington Street
Canton, MA 02021
Table 2. Agenda for plant resources workshop, Boston Harbor Island National Park area,
August 2006.
______________________________________________________________________
Plant Resources Desired Condition Workshop
Boston Harbor Islands National Park Unit
Thompson Island Conference Center
August 22, 2006
9-9:15: Assemble
915-930: Introductions
930-10: Background impetus for meeting; background on GMP and resource
management plans, founding legislation, and potential implications to setting desired
conditions and action items
10-1030: Provide examples of desired conditions and management recommendations
from previous work
1030-1100: Go over preliminary “significant” natural resource/ecological process list
provided by participants and based upon Colwell and Jacobson’s work. Update
significant natural resource list, if necessary. Add significant rankings (local, regional,
national, global), if possible.
11-Noon: Discussion of list and prioritize (prioritize top 5-10); begin desired future
condition formulations
Noon-1230: Lunch (this can be working)
1230-130: For each identified natural resource, formulate desired conditions. Use
examples of desired conditions (provided) and determine if conditions are ideal or
achievable
130-2: Report back on desired conditions
2-230: Discuss and fine-tune desired conditions.
230-330: Develop preliminary management prescriptions for each resource/process or
identify knowledge gaps
330-430: Report back and adjourn
_______________________________________________________________________
Table 3. Significant plant resources of the Boston Harbor Island national park area,
Boston, MA, 2006.
Resource
Level of significance
Rationale
Salt marsh community
Regional
Rose mallow freshwater
marsh
Regional
The presence of salt
marshes on islands is a
relatively rare occurrence in
the northeast. In addition,
the salt marshes on BHI are
rather unique in that they
represent the salt marsh
community type found
within the Gulf of Maine
versus the salt marsh
community type found on
Cape Cod and coastal areas
south of Massachusetts.
Salt marshes support the
rare Rich’s sea blite. The
best salt marsh is found on
Thompson Island but this
community is also found on
World’s End, Long, Calf,
and Snake islands. Snake
Island supports an aesthetic
and diverse marsh. This
community is sensitive to
global climate change and is
being used as a vital sign in
some NPS networks.
This freshwater marsh
found on Long Island
represents the best and
largest freshwater marsh in
the Boston Harbor Islands
in that it supports a largely
native plant community.
Table 3 (Cont.)
Oak-hickory forest
Regional
Maritime juniper/red cedar
community type
Local
Red maple freshwater
swamp
Local
This community at World’s
End represents the largest
native plant association in
the cluster. In addition, this
incidence represents one of
the northernmost
occurrences for the oakhickory forest type in the
United States. Furthermore,
this community represents
one of the few remaining
closed-canopy forests—a
community type that used to
predominate on the inner
islands.
This S1 community type
contains a high percentage
of native plants. It currently
is found on World’s End,
Webb State Park, Langlee,
and Ragged Islands. Its
occurrence on the BHI
represents one of the
northernmost incidences of
this community. This
community is maintained
by salt spray and sandy,
nutrient-poor soils.
This community is
relatively common
throughout southern New
England but is only found
on Grape Island within the
BHI. Freshwater wetlands
are rare on the islands.
Table 3 (Cont.)
Maritime dune community
Local
Maritime shrub community
Local
Maritime erosional cliffs
Local
This S2 community type is
only found on Lovells island.
This may be the only place
that this community is found
in association with a drumlin.
Maintenance of this
community depends on beach
dynamics which may be
threatened by the occurrences
of walls and other hard
structures on Lovells island.
This community type is
common at the BHI and is
dominated by sumac and other
species of shrubs. This
community type is significant
in that it supports large
numbers of songbirds
especially during migration.
This is a community type that
is representative of the
Brewster islands. Continued
disturbance from exposure to
harsh elements may maintain
this community.
These cliffs (S2), composed
of clay soils, are found at Gr.
Brewster, Long, Peddocks,
and Thompson islands.
Coastal seeps that are found at
the base of these cliffs support
populations of rare plants such
as seabeach dock and native
plants such as jewelweed.
Erosional processes that
maintain these cliffs need
further study as increased boat
traffic may be increasing the
natural erosion rate.
Table 3 (Cont.)
Aspen/gray birch forest
Local
Large (100+ acres)
grasslands
Local
Hackberry/sassafras forest
Local
This community is rather
common on the islands with
Grape Island supporting the
best example. Again, this
community represents a
closed-canopy forest, once
common on the inner
islands. Because this is an
early successional forest
type, a disturbance regime
is needed to maintain it.
This community, largely a
cultural resource, is only
found at World’s End.
However, these grasslands
support locally significant
populations of grassland
birds (e.g., bobolinks). The
reproductive success of
these breeding birds should
be studied, however, to
determine whether or not
the World’s End grasslands
are functioning as an
ecological “sink”.
This forest type is only
found at Webb State Park.
It represents a closed
canopy forest—a
community type once
common on the inner
islands. In addition, this
unique assemblage of
hackberry and sassafras is
unusual and hackberry is
rare this far east.
Table 3 (Cont.)
Maritime rock cliffs
Local
Coastal basswood
Regional
Seaside angelica
Local
Rich’s sea-blite
Local
Known from 3 locations
(Langlee, Ragged, Slate) in
BHI, this geologic feature
supports a unique plant
assemblage (S2). The rock
cliffs on Slate Island are
particularly notable where
columbine and lovage are
found. These 2 species of
plants are declining
elsewhere in the state. This
feature on Langlee Island
(pudding stone cliffs)
supports the only known
population of Carolina’s
crane bill in the BHI—a
state species of special
concern.
This taxon may qualify for
listing as state-endangered
if it there was taxonomic
agreement on whether
coastal basswood is a
separate species. It is
currently on the state watch
list of rare species. Coastal
basswood has 7 occurrences
in BHI. Boston Harbor
Island may contain the
largest assemblage of this
species in the northeastern
United States.
This watch-list species is
known from 3 occurrences
within the cluster: Long,
Peddocks, and Calf Islands.
This watch-list species is
found on two islands within
the cluster. It is associated
with healthy salt march
communities on Ragged
and Thompson islands.
Table 3 (Cont.)
Showy goldenrod
Local
Carolina Crane’s Bill
Local
Seabeach Dock
Local
Seabeach needlegrass
Local-extirpated
Potential native Phragmites
on Snake Island
Local
The occurrence of this
watchlist species on
World’s End represents the
only extant population of
showy goldenrod in the
Boston area. This species is
tied to World’s End due to
unique soil requirements.
This species requires open
areas therefore its
occurrence is disturbance
mediated.
This species of special
concern in Massachusetts,
perhaps, has been extirpated
from Little Brewster Island.
Today it is only found on
Langlee Island. This
species is found on rock
cliffs on Langlee island.
This state-threatened
species has been extirpated
from Thompson Island; it is
still found on 3 islands
(Bumpkin, Grape,
Peddocks) within the
cluster. This species is
found on beaches is
associated with the bases of
erosional cliffs
This coastal species has
been extirpated from Deer
Island due to extensive
development. Reestablishment to Deer
Island probably is
impractical.
Native populations of
Phragmites may be in
decline due to
overabundance and spread
of nonnative Phragmites
species.
Table 4. Significant plant resource, desired condition, and management
recommendations for particular groups of islands within Boston Harbor Islands national
park area, August 2006.
Plant resource
Large Island Group;
Thompson, Moon,
Spectacle, Long,
Peddocks,
Rainsford, Gallops,
Georges, Lovells,
Snake, Deer
Salt marsh
Desired condition
Management recommendation
Maintain salt marsh of
native species on
Thompson Island and
Snake Island
Maintain salt marshes free of
non-native Phragmites
On Thompson Island, limit the
spread of Phragmites from the
northern part of the island.
Remove broad-leaved
pepperweed from salt marshes.
On Snake Island, determine if the
Phragmites species present is
native.
Conduct a restoration of the
small but aesthetic and divers salt
marsh on Snake Island.
Maintain natural tidal
flow to salt marshes on
Thompson and Snake
Islands
Maintain salt marsh on
Peddocks Island to
support seaside angelica
Freshwater marsh
Maintain freshwater
marsh of native species
on Long Island
including significant
assemblage of cattail
and rose mallow.
Monitor and remove invasive
non-native species that could outcompete seaside angelica
Limit the spread of non-native
Phragmites.
Monitor and control encroaching
non-native Phragmites, purple
loosestrife, and other invasive
species at Long Island freshwater
marsh.
Table 4 (Cont.)
The maintenance of the
freshwater march on
Long Island will serve
as a model of
restoration of other
freshwater marshes if
any others are located
in BHI.
Maritime erosional
Maintain natural
cliffs
erosional processes of
storm, wind, and wave
on erosional cliffs of
Thompson, Long, and
Peddocks Islands.
Maintain stabilizing
vegetation on tops of
erosional cliffs on
Thompson and
Peddocks Islands
Maritime dunes
Allow natural
processes to shape the
dunes and associated
vegetation community
of Lovells Island.
Hingham Bay Islands; Nut, Sheep, Raccoon,
Bumpkin, Worlds End, Ragged, Langlee,
Maritime Juniper
Natural processes of
woodlands
wind and salt exposure
will remain prominent
in order to maintain the
maritime juniper
woodlands on the
Hingham Bay islands.
The maritime juniper
woodlands will contain
less than 5% cover of
invasive exotic plant
species.
Juniper viriginia will
predominate in this
community type with
less than 20% cover of
other canopy-forming
(native or non-native)
species.
Consider broad-scale removals
of all invasive plants that
threaten the freshwater marsh
on Long Island.
Reintroduce sea beach dock on
Thompson Island at base of
erosional cliffs.
Determine if and how human
disturbance (e.g., boat wakes)
is influencing erosional
processes in BHI.
Consider removing hard
structures that may prohibit
natural dune-forming processes
from occurring.
Grape, Webb State Park, Slate,
Sarah, Button
Aggressively remove invasive
non-native species from
maritime juniper woodlands in
the Hingham Bay Islands.
Initially focus removal efforts
at Webb State Park and
World’s End.
Table 4 (Cont.)
Coastal basswood
Oak-hickory forest
Maritime Rock
Cliffs
Maintain a wooded or
forested community
type with a diversity of
woody species
including coastal
basswood on World’s
End, Ragged, Sarah,
and Raccoon Islands.
At World’s End,
maintain a closedcanopy forest
dominated by native
species (less than 5%
cover of invasive nonnative species) in all
canopy layers with
regeneration of oak and
hickory species.
The Slate Islands rock
cliffs will remain a
sparsely vegetated
community dominated
by native herbaceous
species (less than 5%
coverage of invasive
exotic plants) including
lovage and columbine
with natural processes
of wind and salt
exposures
predominating.
Consider use of low-intensity
prescribed fire to ensure longterm maintenance of this
community type.
Monitor and remove non-native
invasive species from this
community to help ensure
regeneration of oak and hickory.
A buffer zone will be enforced
around the rock cliffs on Slate
Island to keep visitors and rock
climbers from disturbing this
fragile community.
Monitor and remove non-native
invasive species from this
community especially on Slate
Island.
Table 4 (Cont.)
Grasslands
At World’s End existing
size (acreage) and
diversity of grasslands
including associated
ground nesting birds
and populations of
showy goldenrod will
be maintained.
Salt Marsh
At World’s End
maintain vegetated
inter-tidal community
dominated by native
herbaceous species that
supports salt marshdependent wildlife.
Maintain properly timed
disturbance regime (e.g.,
mowing, prescribed burning) to
ensure maintenance of a grass
and herb dominated community
type that supports rare plant
species and grassland dependent
wildlife.
Monitor and remove non-native
invasive plants species especially
vines such as oriental bittersweet
and swallow wort.
Maintain or establish natural
hydrology (e.g., tidal flows).
Maintain or establish physical
conditions above existing salt
marsh to accommodate salt
marsh migration along with sea
level rise.
Maintain marsh free from
anthropogenic disturbances such
as non-native invasive plant
species (Phragmites, pepper
weed) and barriers to tidal flow.
Table 4 (Cont.)
Brewster Islands (all
but the Graves and
Little Brewster)
All communities
(Brewster Islands);
Greater Brewster,
Little Brewster,
Shag Rocks, Middle
Brewster, Outer
Brewster, Calf,
Little Calf, Green,
Graves
Maintain or establish a
natural landscape of
inter-tidal habitats and
maritime upland
communities of diverse
age structures that have
been present on these
islands for at least 100
years; namely, maritime
shrub, maritime scrub,
maritime erosional
cliffs (Greater
Brewster), maritime
rock cliffs (Middle and
Outer Brewster), and
salt marshes (Calf
Island) that exist and
change in response to
natural conditions and
processes such as
climate, fire, overwash,
wind, and salt spray.
Brackish tidal marsh Brackish marsh on
Brewster islands will be
free of anthropogenic
influences like ditches
and barriers.
Evaluate non-native and invasive
species and consider removal.
Implement adaptive management
monitoring of
populations/species/communities.
Evaluate structures (cultural
resources) and consider removal
especially if they are interfering
with natural processes (e.g.,
seawalls and buildings may block
sea spray from plant
communities)
No further construction on
Brewster islands.
Do not maintain ditches in marsh
habitats on Brewster Islands.
Literature cited
Richburg, J. A. and W. A. Patterson III. 2005. Historical description of the vegetation of
the Boston Harbor Islands: 1600-2000. Northeastern Naturalist 12:13-30.
Patterson, W. A., III, J. A. Richburg, K. H. Clark, and S. Shaw. 2005. Paleoecology of
Calf Island in Boston’s Outer Harbor. Northeastern Naturalist 12:31-48.
Elliman, T. 2005. Vascular flora and plant communities of the Boston Harbor Islands.
Northeastern Naturalist 12: 49-76.
Wilson, E. O. 2005. Preface to Boston Harbor Islands National Park Area: Natural
Resources Overview, Special Issue. Northeastern Naturalist 12:2.
Boston Harbor Island Planning Committee. 2004. Boston Harbor Islands Resource
Stewardship Plan, Draft. Boston Harbor Islands National Park Area, Boston, MA.
Foley, M. K. 2005. Significant natural resources of the Brewster Island Cluster: Boston
Harbor Islands National Park Area. Technical Report NPS/NER/NRTR—
2005/024.
National Park Service. 2002. Boston Harbor Islands: a National Park Area, General
Management Plan. Boston Support Office, Northeast Region, Boston, MA.