Table Of ContentRHODORA
JOURNAL OF THE
NEW
ENGLAND
BOTANICAL CLUB
VoK
96 January 1994
No. 885
RHODORA,
Vol. 96, No. 885, 1-29, 1994
pp.
A AND
VEGETATION
FLORISTIC ANALYSIS OF A
CREATED WETLAND
SOUTHEASTERN
IN
NEW
HAMPSHIRE
Donald
Padgett and Garrett Crow
E.
J.
ABSTRACT
The common
artificial creation of wetlands has become a means to mitigate
the effects of wetland alteration due to development. The establishment of
diverse,
functional plant communities and
is a crucial challenging part of a wetland creation
project. This study analyzes plant community structure of a seven year old, ar-
One
tificially created wetland. hundred and four vascular plant species are doc-
umented from New
the study site including two species listed as rare for Hampshire
and
the first state record for an introduced weedy species.
TWINSPAN
The computer program
used species abundance data
to classify
the vegetation into seven cover types. The three plant associations of the open
water Chara
habitat were: cover type, Potamogeton pusillus cover type, and the
Potamogeton The
natans cover
type. four plant associations of the emergent
habitat were: Eleocharis smallu cover Typha
type, cover Juncus
latifolia type,
effusus-Phalahs arundinacea cover and Carex
type, a cover Each
stricta type.
cover type and associated habitat was described and
delineated.
Key
Words:
wetlands, wetland
floristics, mitigation, rare plants
INTRODUCTION
Encompa
ms
marshes
as freshwater
swamps,
bogs, sloughs, ponds and lakes, rivers and streams
marshes
biomes
Mitsch
and
productivity associated food-chain support, wetland
ecosys-
tems
oerform
are
vital in
(Goodwin
and
Burke
Niering, 1974; 1988; Larson,
et 1988).
al.,
The
rather late recognition of wetland values and functions over
rm
1
Rhodora
96
2 [Vol.
Most
which wetlands are being destroyed. important, the
rale at
environment
vital role wetlands play in the overall quality of the
has been recognized and a variety of efforts are being im-
finally
means
plemented provide conservation.
to a for their
One
has been developed conserve wetlands
strategy that to
is
Wetland com-
termed wetland mitigation. mitigation reduces or
pensates for the negative impacts on aquatic ecosystems imposed
by development by creating or restoring wetland areas
artificially
become
(Savage, 1986). Mitigation has an integral part of wetland
and Wetland
protection conservation mitigation
policies. at-
tempts to restore to an area those functions of a wetland that are
impacted
or destroyed.
The
primary goal of wetland creation or restoration projects
aims wetland Wetland
typically at restoring lost functions. cre-
aim an
ation efforts additionally at creating area that at least
is
the same size as the area lost and the estabhshment of certain
wetland vegetation types (Lowry, 1990; Kruczynski, 1990).
The
establishment of hydrophilic vegetation wet-
crucial in
is
land mitigation projects they are to imitate successfully natural
if
Wetland some
wetland ecosystems. vegetation provides of the
important functions and values inherent wetlands (Good
in et
al.,
Mitsch and and
1978; Gosselink, 1986) creates suitable habitats
The
for wildlife (Weller, 1978). establishment of diverse, func-
tional wetland plant communities a challenging part of miti-
is
and Crow,
gation projects (Padgett in press).
The
objective of the present study to provide a detailed
is
vegetation analysis and total floristic inventory of a seven year
old, artificially created, freshwater wetland located in southeastern
New
Hampshire.
History
Site
During the winter of 1985-86, the Hospital Corporation of
America (HCA) created a freshwater wetland under the Section
Army
compensate
404 guidelines of the U.S. Corps of Engineers to
new
for the filling of a wetland at the construction site of a regional
New
The
Portsmouth, Hampshire. land area desig-
hospital in
nated for the creation of the compensatory wetland was an aban-
from
doned gravel pit located approximately 3 miles the hospital
NH
(Rockingham
the southern end of Portsmouth, Co.)
in
site
The
(Michener of the mitigation area 13
ct al, 1986). size (ca.
Crow-Wetland
and
Padgett
1994] 3
was
acres) similar to the size of the area lost due to the hospital
construction.
Wetland
construction began and
in the of 1985 continued
fall
through
the winter of 1986. Basins were excavated and graded
to
form
a sinuous configuration of open water pools and marsh
areas
(Michener The
wetland and new
et al., 1986). soils peat at the
im
material
through and 6-12"
the winter eventually spread as a top dressing
over the excavated
basins.
The
primary
strategy to vegetate the newly created basins was
allow
to for the natural colonization of wetland Therefore
plants.
m
serve
holding
urally large quantities of plant seeds and vegetative pro-
(Michener
primary
Groundwater
flow westward,
discharging
into the adjacent
is for-
swamp
summer
dammed
after construction, beavers the small outflow channel.
approximately
above
the design
elevation.
Site Description
The
H.C.A. Portsmouth
wetland
a created freshwater wetland
is
Some
consisting of primarily herbaceous and
aquatic
plants. tree
shrub areas exist on several upland islands and pool margins.
Open
water areas form sinuous configurations around these
is-
maximum
The
lands. depth of the open water areas approxi-
is
mately two The
meters. created wetland surrounded by upland
is
forest communities on the northeastern and southern and
sides,
A
community
wetland on northwestem
a forest the
side. dis-
woody
turbed, open, sandy area with few surrounds
plants the
wetland on
the southeast
side.
AND
MATERIALS METHODS
Vegetation Analysis
Samphng
Vegetation data were collected during July of 1992.
was done using a systematic sampling method (Mueller-Dombois
Rhodora
4 [Vol. 96
and Ellenberg, 1974). Thirteen transects were established across
m
A
the wetland at 20 meter intervals. single 0.5 x 0.5 quadrat
was placed at every five meters of transect for a total of 284 sample
and on banks and upland
Trees, shrubs herbs occurring the
plots.
on the islands throughout the wetland were not included in
sites
the sampling.
A
was
visual estimate of percent cover recorded to estimate
The was
abundance. primary focus of the vegetation analysis
vascular plant species. However, because of their relative abun-
dance Chara cf vulgaris and Ricciocarpus natans, two non-vas-
cular aquatic plants, were included in the vegetation analysis.
Cover was defined as the vertical crown or shoot-area projection
(Mueller-Dombois
per species in relation to the reference area
and
EUenberg,
1974).
TWINSPAN
(Two-Way
The
data were analyzed using Indi-
program.
cator Species Analysis), a fortran classification analysis
The program of samples and then
constructs a classification
first
based on this classification, constructs a classification of species
according to their ecological preferences (Hill, 1979).
TWINSPAN
groups the quadrat samples according to the flo-
similarity of members. Using these groups as a basis,
ristic its
form There
species are clustered to hierarchial dichotomies. are
three ordinations involved in determining a dichotomy: a pri-
1)
mary made method
ordination, by a of reciprocal averaging;
2)
determined from
a refined ordination, using differential species
the primary ordination; and an indicator ordination, using
3)
Corresponding
highly preferential species (Hill, 1979). to the
Braun-Blanquet cover-abundance of 50 and 75
scale 25,
0, 5,
percent (Mueller-Dombois and Ellenberg, 1974), abundance data
TWINSPAN
of "pseudo-species" were classified at cut levels of
4 and 5 respectively. Ultimately, a two-way table gen-
1, 2, 3, is
and
erated grouping similar quadrat samples across the top similar
down
species the side (Padgett, 1993).
left
A
map
was prepared based on cover types
vegetation (Figure
2)
of quadrats along the 13 transects to give a visual estimate of the
pattern of distribution of the seven cover types.
Study
Floristic
An
inventory of the vascular plants of the was undertaken
site
during the 1992 season. Voucher specimens were collected
field
Crow—
and Wetland
Padgett
1994] 5
284
II 143
0|x:ii walci ly[x:s EiTicigcnl types
54 87 134
Cham
co\'cr Eleocharis swaUii
I}'|x:
cover type
68 55 79
\9
roinnwgeioii iuuhjis Pofamogcfr)!! pusilliLS Typha lalifolia
cover ly|x; cover type cover type
65
14
Carex
JuUCliS slrirln
efflLSlLS-
Phalaris arimdiuacea co\'cr type
cover type
TWINSPAN
Figure analysis showing the seven plant cover types classified
1.
Numerals number
at four hierarchical levels. represent the of quadrats included
each dichotomy.
in
Herbarium
Hampsh
Nomenclature follows Aquatic and Wetland Plants North-
of
North America (Crow and and Manual
eastern Hellquist, in press)
and
of Vascular Plants of Northeastern United States Adjacent
Canada and
(Gleason Cronquist,
1991).
AND
RESULTS DISCUSSION
The
construction of the H.C.A. Portsmouth wetland has created
a unique environment, allowing for a natural colonization and
emergence of wetland plant The various micro-habitats
species.
formed by the gradual slopes of the basins and integration of
As
raised islands provide a heterogeneous ecosystem. a
result,
concentric vegetation zones have developed according to the eco-
logical affinities of species characteristic of natural wetland sys-
The
tems. vegetation patterns of the are typical of those
site
and
described for inland freshwater wetlands (Mitsch Gosselink,
Hammer,
1986; 1992; Weller, 1978; Curtis, 1959). Generally, for
most inland wetlands, sedges {Carex) and rushes (Juncus) occupy
Rhodora
6 [Vol. 96
wet-meadow
the areas gradually passing into the shallow water
areas colonized by Cattails (Typha), Bulrush {Scirpus) and Pick-
Weed
The
open
{Ponlederia cordata). deeper, water areas are
erel
colonized by submerged species {Utricularia) and floating leaved
{Potamogeton and Nuphar),
species
Plant Cover Types
TWINSPAN
The was
wetland vegetation classified using into
seven cover types (Figure Data from 284 quadrats were an-
1).
alyzed and 67 species were clustered four hierarchical divisions
at
into the seven cover types which could be visually recognized in
the
field.
The dichotomy grouped the 284 quadrats into two major
first
groupings, with 141 quadrats representing the open water cover
types, and 143 quadrats representing the emergent cover types.
At the second level of clustering, 54 quadrats of open water types
Chara
were distinguished as the cover type, with 87 quadrats
remaining to be sub-clustered. At the third level 68 quadrats
represented the Potamogeton natans cover type and 19 quadrats
Potamogeton
defined the pusillus cover type.
TWINSPAN
grouped the 143 quadrats the emergent cover
in
type group into four cover types (Figure At the second
level
1).
the Eleocharis smallii cover type was recognized quadrats). At
(9
the third level the Typha cover type was distinguished
latifolia
(55 quadrats), while the Juneus ejfusus-Phalaris arundinacea (65
and Carex
quadrats) stricta (14 quadrats) cover types were not
defined the fourth
until level.
The
clustering of the quadrats at the divisional level clearly
first
correlates with the two primary habitats designed for the
site
The
open water cover occupy where
creation. types the areas the
Most
water too deep be colonized by emergent of
to species.
is
the open water areas were vegetated by floating-leaved, free-float-
and submerged However, some remained
ing species. areas de-
void of vascular plants. For instance, one open pool was heavily
colonized by filamentous Although cover were
algae. three types
recognized as the open water areas, these were not characterized
by distinct vegetation zones. Instead these cover types occurred
mosaic
in a pattern.
The meadow
emergent cover types represent the marsh or wet
regions designed for the wetland. These areas are defined by a
Crow—
Padgett and Wetland
1994] 7
topographic
gradient beginning in the shallow fringe areas of the
marsh
Consequently, the emergent
when
compared
nal patterns
to th
emergent cover most
types are the
mmance
emergent
mergent
cover types than in the open water cover areas
OPEN WATER COVER
TYPES
Potamogeton Cover Type
natans
The
Potamogeton
natans cover type the largest plant asso-
is
ciation of the open water types (Figure defined by the 68
2),
TWINSPAN.
Of
quadrats clustered by the seventeen species that
dom-
community,
characterize the the floating-leaved natans
P.
is
35% 90%
and The
inant with cover frequency (Table sub-
1).
merged Najas minor and Utricularia gibba are sub-dominants
9%
11%
and
with covers, respectively, although U. gibba has a
The
morphology
significantly higher percent frequency. delicate
of U. gibba does not allow for high percent coverage.
The
cover type easily discernible by the presence of broad
is
floating leaves of Potamogeton natans that form an expansive
cover on the surface of the water. This floating-leaf layer was so
extensive in certain portions of the wetland, particularly in the
northwestern few open water were
pool, that surface areas present.
mean
Although the cover of P. natans was very extensive, the
percent cover of P. natans throughout the entire cover type was
only 35%. In areas that were sparsely populated with natans
P.
submerged species, such as Najas minor, Utricularia gibba and
were
P. pusillus, frequent.
Chara Cover Type
The
Chara
cover type one of
the larger plant associations of
is
open The community
the water types (Figure can be
charac-
2).
m
minates
Rhodora
96
8 [Vol.
Chum CT
sp.
CT
Potaniogeton
nutans
CT
Polumogeton
pusillus
CT
Eleocharis
smullii
CT
Typha
latifoUa
JuncKs
ejfitsus-Phalaris
CT
anindinucea
CT
Carcx
strictu
The
Figure distribution of the seven plant cover types of the H.C.A. Ports-
2.
CT =
mouth Cover
created wetland.
type.
Crow-Wetland
and
Padgett
9
1994]
Mean
Table percent cover and percent frequency for species in the Pota-
1,
<
mogeton natans cover type (species with cover percent are excluded).
1
% %
Species Cover Frequency
Potamogeton
natans 35 90
Najas minor
11 15
Utricularia gibba 9 82
Potamogeton
pusillus 2 15
Eleocharis acicularis 2 6
Lemna
minor
19
1
Ludwigia
palustris
1 1
commonly
oTChara were observed as monotypic colonies or with
few other species. However, Utricularia gibba and Potamogeton
natans are sub-dominant components of the community. The
community
remaining species of the (Table with the exception
2),
more
of of emergent
P. pusillus, are characteristic areas.
The weedy Chara
nature of has allowed
to successfully col-
it
More
open
onize the water areas of the typically associated
site.
with hard water Chara has been found dominate deeper
to
sites,
amounts
waters of lakes producing large of biomass (Rickett,
The Chara community
1921). exists in the deeper pools of the
where
wetland, the cover of floating leaved species relatively
is
low.
Potamogeton Cover Type
pusillus
This cover type characterized by the submerged Pondweed
is
Potamogeton
species, pusillus (Table This plant association
3).
Table Mean percent cover and percent frequency for species in the Chara
2.
<
cover type (species with cover percent are excluded).
1
% %
Cover Frequency
Species
Chara 98
vulgaris 81
cf.
gibba 56
Utricularia 11
Potamogeton natans 37
9
Eleocharis acicularis 3 7
Ludwigia
palustris 9
1
Potamogeton
pusillus 7
1
Juncus 4
articulatus
1
Typha 4
latifolia
1
Rhodora
10 [Vol.96
Mean
Table percent cover and percent frequency for species in the Pota-
3.
<
mogeton pusillus cover type (species with cover percent are excluded).
1
% %
Cover Frequency
Species
Potamogeton 36 95
pusillus
Pontederia cordata 12 21
Elcocharis aciculans 26
5
Potamogeton nutans 4 47
42
Utricularia gibba 3
Lemna
minor 37
1
Najas minor 11
1
Potamogeton
amplifolius 5
1
covers the smallest portion of the open water areas and was rep-
resented by only 19 quadrats. The Potamogeton pusillus cover
type occurs in scattered areas within the open water portions of
most
the wetland, typically close to the emergent vegetation cover
Two
types. of the largest areas where this cover type predom-
is
shown
inate are in Figure Although, this cover type primarily
2.
is
composed
submerged and
of emergent
free-floating species, the
Pontederia cordata sub-dominant component.
a
is
EMERGENT COVER
TYPES
Juncus ejfusus-Phalaris arundinacea Cover Type
The
Juncus arundinacea cover most
effusus-Phalaris type the
is
Of
floristically diverse cover type of the entire wetland. the 55
species occurring in the cover type, Juncus ejfusus and Phalaris
arundinacea are co-dominant, with a collective cover value of
41%
(Table This cover type generally extends from the upland
4).
shores or islands to the edge communities of the Typha
latifolia
cover type (Figure However, some pool margins
are directly
2).
surrounded by cover where Typha
type does not dominate.
this
The
areas of the Juncus arundinacea cover
effusus-Phalaris type
are rarely inundated for any extended period of time. Most por-
tions remain wet damp, allowing wide range of wetland
to for a
species to exist. This mostly low-growing, herbaceous plant com-
munity some woody components
has such Alnus incana
as
ssp.
rugosa, Acer rubrum and Cornus occupying various
spp. portions.
among
Unique
cover both annuals and
types, perennials are well
The
represented within Cyperaceae
this association. best repre-
is
