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Seabloom Wiedemann 94
Distribution and Effects of Ammophila breviligulata Fern. (American Beachgrass) on the
Foredunes of the Washington Coast
Author(s): E. W. Seabloom and A. M. Wiedemann
Source: Journal of Coastal Research, Vol. 10, No. 1 (Winter, 1994), pp. 178-188
Published by: Allen Press
Stable URL: http://www.jstor.org/stable/4298202
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Journal of Coastal Research 1 10 1
1 178-188 1 Fort Lauderdale, Florida I Winter 1994
Distribution and Effects of Ammophila breviligulata Fern.
(American beachgrass) on the Foredunes of the Washington Coast
E.W. Seabloomt and A.M. Wiedemannt
tDepartment of Botany tThe Evergreen State College
353 Bessey Hall Olympia, WA 98505, U.S.A.
Iowa State University
Ames, IA 50011-1020, U.S.A.
ABSTRACT
SEABLOOM, E.W. and WIEDEMANN, A.M., 1994. Distribution and effects of Ammophila breviligulata
Fern. (American beachgrass) on the foredunes of the Washington coast. Journal of Coastal Research,
?? 10(1), 178-188. Fort Lauderdale (Florida), ISSN 0749-0208.
Since the turn of the century, the foredunes on the west coast of North America have become dominated
by Ammophila arenaria due to extensive sand stabilization plantings. Ammophila breviligulata was
planted less extensively than A. arenaria. However, A. breviligulata has come to singularly dominate the
foredunes of Washington in the southern half of the state and its range extends north along the entire
coast. By comparing the distribution of current A. breviligulata and A. arenaria communities with historic
shorelines, it was found that this invasion occurred in the last 50 years and the locus of the invasion was
determined. A comparison of foredunes dominated by A. breviligulata with existing A. arenaria foredunes
shows that this colonization has had minimal impact on the species diversity of the dunes, but it has
resulted in a lowering of the mean height of the foredune crests.
ADDITIONAL INDEX WORDS: Ammophila arenaria, dune morphology, introduced species, coastal
plant communities.
INTRODUCTION feature in the coastal ecosystem, replacing many
of the native communities in the foredune habitat
Ammophila breviligulata Fern. (American
beachgrass) is native to the East Coast and Great (PAVLIK,1983).
Lakes Region of North America (BALDWIN and Because of the overwhelming success of the A.
arenaria plantings, there has been little use of A.
MAUN, 1983; GLEASON and CRONQUIST, 1963;
OLSON, 1958a,b; HITCHCOCK, 1950; COWLES, 1899), breviligulata for dune stabilization on the west
and it has been intensively studied within this coast. Accordingly, very little information on the
native range (MAUN and BAYE, 1989). It is a pi- status of A. breviligulata on the west coast of
oneer species adapted to dynamic coastal dune North America is available. A review of this lit-
systems where it is, typically, the major dune erature and the collection history leads to the
building plant species present (DISRAELI, 1984; conclusion that A. breviligulata exists on the west
DUNLOP and CROW, 1985). It rapidly becomes se- coast only as persistent remnant populations
nescent when dune areas stabilize and is then (MAUN and BAYE, 1989; BARBOUR et al., 1975;
rapidly replaced by other species (DISRAELI,
1984; BARBOUR et al., 1976).
VAN DER VALK, 1975; ELDRED and MAUN, 1982). The only sizable planting of A. breviligulata
Ammophila arenaria (L.) Link (European that has been recorded was a part of the Warren-
beachgrass or marram grass) is a native of Europe ton Dunes Stabilization project on the Clatsop
similar to A. breviligulata in its adaptations to Peninsula in Oregon near the mouth of the Co-
the coastal dune ecosystems. A. arenaria has been lumbia River. The Soil Conservation Service un-
widely planted on the west coast of North America dertook this project in 1935; and up to that time,
for dune stabilization since the early 1900's. It has
it was one of the largest dune stabilization pro-
become naturalized along nearly the entire coast-
line (BARBOUR and MAJOR, 1988; HITCHCOCK et jects in the western United States. A nursery was
established at Warrenton, Oregon, and 1,214 ha
al., 1969; HITCHCOCK, 1950) and is a dominant
were progressively stabilized with a variety of spe-
cies including A. breviligulata (SCHWENDIMAN,
92133 received 25 November 1992; accepted in revision 27 March 1993. 1977). A. breviligulata from this nursery was also
Ammophila breviligulata on the Washington Coast 179
planted at the south end of the Long Beach Pen-
insula at Ilwaco (Figures 1, 2).
San Juan
At present, the densest populations of A. brevi- Archipelago
ligulata are located between the mouth of the Shi
Cape Flattery
Shi Beach Port
Columbia River and Westport, 75 km to the north.
Port Angeles
In this area, A. breviligulata is almost singularly
dominant on the foredune, the first dune land- Olympic
Peninsula
ward of the beach. The dominance of A. brevili- Seattle
gulata decreases beyond these boundaries to the Q Copalis River
north and south. This distribution pattern indi- o Grays Harbor Olympia
cates that the Clatsop and Ilwaco plantings were U Chehalis River
.H Willapal Ba
the likely source of the naturalized populations 4-4 Long Beac
-H Peninsula
of A. breviligulata now found on the Washington U
and Oregon coastal dunes.
The primary dispersal mechanism of A. brevi-
ligulata is through waterborne rhizome fragments
River
Washington
Columbia
(MAUN,1984), and the dominant current on the Sand Lake Oregon
southern Washington coast is the northward long-
North
shore current (PHIPPS, 1990). If the source of the
A. breviligulata invasion was the Clatsop and Il- 50 km
waco plantings, the longshore current would have LJ
rapidly spread rhizome fragments along the ac-
Figure 1. Map of the area surveyed for the distribution of
creting shoreline of the Long Beach Peninsula Ammophila breviligulata and Ammophila arenaria. The lo-
allowing A. breviligulata to colonize the beach cation of Figure 2 is shown as an inset.
and replace A. arenaria as the dominant dune
forming species.
If this scenario were the case, it should be pos-
sible to locate the transition from one Ammo- typical of prograding shorelines in this area. North
phila species to the other. Since both species of this point the rocky headlands are close to the
have extremely low vegetative and sexual repro- beach and prevent any major dune formation
ductive rates in stabilized dune areas (OLSON, (Figures 1 and 2).
1958a), it is unlikely that there would have been The objectives of this research were threefold:
significant invasion by either population in the to determine the source, location, and time period
highly stable backdune areas. WILLIS (1963) of the major introductions of the exotic species
found that even fertilization could not stimulate A. breviligulata; to establish the current range
senescent Ammophila populations to the point and habit of A. breviligulata on the Washington
of expansion. Coast; and to determine if the A. breviligulata
If there is no invasion in the backdune areas and A. arenaria foredunes differ significantly in
and the transition zone is stable, then the border structure or plant species diversity.
between the two communities actually represents METHODS
the location of the historic shoreline or foredune
crest when A. breviligulata replaced A. arenaria Study Sites
as the foredune's dominant grass. The quantitative fieldwork for the determina-
The timing of the introduction of A. brevili- tion of the source and timing of the introduction
gulata was determined by comparing the A. brev- of A. breviligulata and the characterization of the
iligulata/A. arenaria transition zone to the lo- current Ammophila dunes took place on the fore-
cation of historic foredunes as determined from dunes of the Washington Coast from North Head
a chronological sequence of aerial photos. The near the state's southern border at the mouth of
southern portion of the Washington coast is char- the Columbia River (460 17' 30" N Lat) north to
acterized by a broad band of sand beach and dunes Westport (460 52' 30" N Lat). In addition, the
as far north as the Copalis River (470 08' 00" N distribution of A. breviligulata was surveyed along
Lat). These dunes are examples of the parallel the western and northern coastlines of Washing-
dune system described by WIEDEMANN (1984) as ton as far east as Port Angeles and the north half
Journal of Coastal Research, Vol. 10, No. 1, 1994
180 Seabloom and Wiedemann
Field Sampling
Harbor
The quantitative fieldwork on dune shape and
Grays
105 vegetative characteristics was completed between
Westport July and October of 1988. A second series of 34
Twin Harbors
transects, 19 on the Long Beach Peninsula and
State Park o10 15 between Cape Shoalwater at the north edge of
the mouth of Willapa Bay and Westport, were
Cape
Shoalwater Willapa selected randomly. In addition, several transects
River
were established on the specific dunes where A.
Leadbetter
Point arenaria was dominant. None of these transects
coincided with those used for the historic shore-
line study.
illapa
Ocean Park ay The foredune profile was mapped by measuring
the height at 5 m intervals (survey stations) along
0)
u 103 a 50-75 m transect (depending on foredune width)
op
U running perpendicular to the foredune. This pro-
Long Beach 10 file was used to calculate the slope, length, and
Seaview
North Head Ilwaco
height of the west face of the foredune. The tran-
sect started at the lower limit of the vegetation.
Columbia
River This point was given an arbitrary elevation of zero
Clatsop, Spit -~
m. The dune crest height was measured indepen-
Warrenton * 30
dently, if it did not coincide with one of the survey
stations. In addition, the following data were col-
North lected at these survey stations within a 20 by 50
25 km1 cm rectangular quadrat placed perpendicular to
the transect line and centered on each survey stake:
Figure 2. Map of the Long Beach Peninsula, and the site of
the quantitative dune morphology and population studies. (a) the total number shoots of each species of
Ammophila in the quadrat; (b) The width of the
second lowest live leaf at a point 2 cm distal from
of the coast of Oregon as far south as Sand Lake the ligule on the culm nearest the southeast corner
(Figures 1 and 2). of the quadrat; (c) the number of Ammophila
inflorescences in the quadrat; and (d) the % cover
The Introduction of A. breviligulata
(using the 1-10 Domin Cover Class scale) within
The localization of the A. breviligulatalA. ar- the quadrat of all plant species, vegetative litter,
enaria transition zone on the Long Beach Pen- and bare ground.
insula at 17 transects was mapped onto a 1:12,000 A. breviligulata and A. arenaria generally oc-
scale aerial photograph series taken on 31 July curred in discrete stands, and were readily dis-
1988, one month prior to the time the measure- tinguishable in the field on the basis of ligule
ments were taken. Initially, 21 transect locations length, inflorescence morphology, phenology, and
were chosen at one mile intervals beginning at the foliar characteristics (SEABLOOM, 1991). Speci-
Seaview beach access and running north to Lead- mens of both species from a number of represen-
better Point, however, four locations were elimi- tative locations in Washington and Oregon were
nated due to human disturbances in the backdune deposited in the University of Washington Her-
area. barium, Seattle, Washington.
The historic foredune position was determined Because the transect profiles varied widely, each
using a series of historic aerial photos (1949, 1964, transect was divided into four habitat zones to
1970, 1974, and 1982). The location of the fore- facilitate comparative analysis (Figure 4). This
dune for each of these years was determined at zonal approach permits the comparison of the dis-
each transect and mapped onto the 1988 photo tinct environments present on each foredune by
series. It was then possible to measure the dis- correcting for the specific profile of each foredune.
tance to the east or west that each historic dune The beach (Zone I) extends from the seaward line
lay from the A. breviligulatalA. arenaria tran- of vegetation east to the seaward toe of the dune;
sition zone (Figure 3). the windward slope (Zone II) extends from this
Journal of Coastal Research, Vol. 10, No. 1, 1994
Ammophila breviligulata on the Washington Coast 181
A. breviligulata A. arenaria
30
S* 1941
a 1964
S* 1970
v 1974
0 25 o 1981
. 1988
C,)
o
4-
.~- 20
0
z
E S
15
10
5
400 300 200 100 100 200 30 400
Meters West of Transition Meters East of Transition
Figure 3. Location of the transition between the Ammophila breviligulata and Ammophila arenaria communities in relation to
the locations of six historic foredunes on the Long Beach Peninsula.
Journal of Coastal Research, Vol. 10, No. 1, 1994
182 Seabloom and Wiedemann
Beach I Windward Slope I Leeward Slope I Backdune
I i
est
Figure 4. Four Zones of the coastal foredune.
point to just past the crest of the foredune; The North Head at the southern end of the Long Beach
leeward slope (Zone III) extends from the limit Peninsula to Westport, where it is present in near-
of high sand accretion just past the foredune crest ly monospecific stands in Zones II, III, and IV
to the landward toe of the dune; and the backdune (Figures 1 and 5). On the dune systems north of
(Zone IV) includes all of the area east this point. Westport both species of Ammophila alternate as
The vegetative and dune profile data were com- the dominant foredune species. The only sizable
pared between dune zones using an ANOVA fol- unmixed A. arenaria foredune community locat-
lowed by a Fisher's Test for Least Significant Dif- ed in Washington was at Twin Harbors State Park
ferences to locate the sources of the detected south of Westport where five acres was planted
variance. An ANOVA was also used to compare in 1981 as part of a cooperative project between
A. breviligulata and A. arenaria populations. The the Soil Conservation Service and the Washing-
Simpson and Shannon indices were used to com- ton Parks and Recreation Commission. This pop-
pare species diversity between dune zones and ulation now covers about 3 km of coastline.
Ammophila communities (BROWER and ZAR, The second niche A. breviligulata occupies is
1977). the area between the shoreward toe of the fore-
RESULTS dune and the lower limit of vegetation (Zone I).
In this area, it creates hummocks, usually less
The Introduction of A. breviligulata than 2 m in diameter, along with a number of
In 0.76 of the transects, the transition between native hummock forming species, including Am-
A. breviligulata and A. arenaria dominated stands brosia chamissonis (silver bursage), Cakile eden-
occurred between the location of the 1964 and the tula (American searocket), and Abronia latifolia
1974 or the 1970 and 1974 shorelines. In all but (yellow sand-verbena).
one transect, the transition zone was bounded by In this more marginal habitat, A. breviligulata
the 1941 and the 1974 shorelines. This one vari- can be found along the entire Washington coast
ation occurred because there was no information as far north as Shi Shi Beach and south to Sand
available prior to 1964 at that location (Figure 3). Lake in Oregon, although its frequency decreases
markedly at the northern and southern limits of
Current Range and Habit of A. breviligulata this range. A. breviligulata can also be found scat-
Within its current range on the west coast, A. tered on sand bars and spits in Willapa Bay and
breviligulata occupies two distinct habitats. First, Grays Harbor, although this habitat is dominated
it is the dominant vegetation on the foredunes in by the native Elymus mollis (American dune-
the quantitative study area which ranges from grass) (Figure 1).
Journal of Coastal Research, Vol. 10, No. 1, 1994
Ammophila breviligulata on the Washington Coast 183
6 4
5 a, 33
CO
4 O
LL 2
0
3 0. 1
C
E 2 0
0 35
E
( 30
0
LL 25
c 20
Zone I Zone II Zone III Zone IV
A. breviligulata
III|||I| A. arenaria
8 10
Figure 5. Comparison of the dominance of Ammophila brevi- a
ligulata and Ammophila arenaria in each of the four Dune 0
Zones as indicated by their respective cover of live plants av- 0.5
eraged over the entire population of samples.
au
LL
0.4 -
5 0.3
Neither species of Ammophila was located along 0
0.2
o
the northern edge of the Olympic Peninsula, but a-
o 0.1
A. breviligulata is present at Port Townsend and
both A. breviligulata and A. arenaria are present 0
in the San Juan Archipelago (Figure 1). North Central South
Field observations of the A. breviligulata pop- Figure 6. Comparison of the mean height, slope, and length
ulation on the Long Beach Peninsula distin- of the west face of the foredunes in the three Geographic Units
on the Long Beach Peninsula.
guished three distinct geographic units on the ba-
sis of dune shape and vegetative characteristics.
The South Unit extends from North Head to Long
Beach and is characterized by a low foredune with the plant communities in these three Units was
minimally developed beach plant communities not found to be significantly different (Figure 7).
characterized by Cakile edentula. The Central The percent cover of live A. breviligulata plants
Unit extends from Long Beach, north to Ocean and vegetative litter increases markedly from the
Park and has a low A. breviligulata foredune beach to the dune, but remains constant on the
somewhat similar to the southern Unit; however, entire foredune (Figure 8A,F). Stem density
Zone I in this Unit has a well developed vegetative reaches its maximum on the seaward slope of the
community dominated by Ambrosia chamissonis dune in Zone II (Figure 8B) and flowering occurs
with Cakile edentula and Abronia latifolia as as- almost entirely in Zone I (Figure 8C). Leaf width
sociated species. The North Unit extends from also appears to be an indicator of the vigor of the
Ocean Park north to Leadbetter Point and has a individual plants since it diminishes steadily with
steep foredune of A. breviligulata with little or increasing distance from the beach. The width
no beach vegetation (Figure 2). remains equivalent in Zones I and II but drops
An ANOVA comparison of these three geo- consecutively in Zone III and again in Zone IV
graphic units showed that their foredunes differed (Figure 8D). The presence of bare ground in the
significantly in height of the crest, length of the transects drops as {he cover value of A. brevili-
windward face, and slope of the windward face. gulata increases and the individual vigor of the
In all three parameters, the only equivalency was plants is declining (Figure 8E).
between the height of the dunes in the South and This decrease in the vigor of the Ammophila
Central Units (Figure 6). The species diversity of stands was paralleled by an increase in species
Journal of Coastal Research, Vol. 10, No. 1, 1994
184 Seabloom and Wiedemann
within a stand rather than the importance of the
0.8
species in the study area as a whole. The stem
density was significantly (P = 0.012) greater for
0.7 A. arenaria (203 stems/m2) than for A. brevili-
x o.s gulata (79 stems/m2).
0.4 Comparing the means of the three dune shape
parameters for the entire population of foredunes
r 0.4 showed that the population of A. arenaria dunes,
0
a 0.3
E
which had a mean elevation of 4.52 m, were sig-
0.2 nificantly taller than the A. breviligulata dune
0.1
which had an overall mean of 2.82 m. However,
while the A. breviligulata dunes were only 67%
0
as long as the A. arenaria dunes, the ANOVA
3.5 failed to detect a difference between the two pop-
ulations (P = 0.147). The slope of the windward
x face of the dunes associated with both species of
2.5 Ammophila was nearly identical and there was
2-
no difference detected in the ANOVA (Table 1).
0
o 1.s
DISCUSSION AND CONCLUSIONS
c
The current locus of A. breviligulata on the
west coast supports the conclusion that the col-
0.5
onization source was the Clatsop and Ilwaco
0 plantings which began in 1935. This conclusion is
Zone I Zone II Zone III Zone IV
in accord with the timing of the colonization of
NorthUnit - CentralUnit %South Unit the Long Beach Peninsula foredunes as deter-
IIIIIIl
mined by examining the distribution of A. brevi-
Figure 7. Comparison of the Simpson and Shannon Species
Diversity Indices of each of the four Dune Zones between the ligulata and A. arenaria in relation to the location
three Geographic Units on the Long Beach Peninsula. of historic shorelines. These findings indicate that
A. breviligulata replaced A. arenaria as the pri-
mary foredune colonizing species between 1941
and 1974, and it is most likely that the majority
diversity in the stable backdune areas as com- of the colonization occurred in the ten year period
pared to the high depositional environment of from 1964 to 1974 (Figure 3).
Zones I and II (Figure 9). The maximum stem density in Washington
populations (Figure 8B) occurs in a similar suc-
Comparison of A. breviligulata and A. arenaria cessional stage and within the range of values giv-
Foredunes en for stands along Lake Michigan, which range
A comparison of the foredune communities from 110 to 150 stems/m2 and the cover values of
dominated by A. breviligulata versus those dom- 50 to 59% (KRAJNYK and MAUN, 1981; OLSON,
inated by A. arenaria showed equivalent species 1958a). However, flowering occurs almost entirely
diversity indices in all the Zones except Zone II in Zone I in Washington (Figure 8C) while on
(Figure 10). In this Zone, A. arenaria foredune Lake Erie flowering reaches its peak in the ado-
communities have a slightly higher species diver- lescent growth phase when stem density is the
sity than the A. breviligulata dominated fore- highest (KRAJNYK and MAUN, 1981). This is
dunes. Both the Simpson and the Shannon in- equivalent to Zone II where the flowering rates
dices show this difference at the same confidence were low for the Washington populations (Figure
level. 8C).
The overall stem density between the Am- While the overall % cover of A. breviligulata
mophila species was compared over the entire set shows a marked increase from the beach to the
of samples. All of the samples with density values dune, the cover values remain relatively constant
of zero were excluded from this comparison. This on the foredune proper in Zones II, III, and IV
was done in order to compare mean stem density (Figure 8A). However, the vigor of the individual
Journal of Coastal Research, Vol. 10, No. 1, 1994
Ammophila breviligulata on the Washington Coast 185
7
n C6
A. 120 B.
E8o
,- 3 E 60
-2 0 40
a)
o1 20
0 0
I II III IV I II III IV
35
-14
30 -12
E
Cq25 E
Ilo
E20 8
0 8
I II III IV I II III IV
12 10
o
015
E. 9F.
8
a)2
(.8 7
0 - 7
0)6
>2 0510
0 0 0
I II III IV I II III IV
Geographic Zone Geographic Zone
Figure 8. Comparison of six indicators of Ammophila breviligulata population vigor between each of the four Dune Zones throughout
the entire set of transects. Total cover of live plants, stem density, flower shoot density, leaf width, cover of bare ground, and cover
of litter are shown as graphs A-F respectively. Underlined Dune Zones are equivalent at a = 0.05.
plants diminishes as indicated by decreasing leaf Thus, the overall ecology of A. breviligulata on
width and depressed vegetative and sexual repro- the west coast in its range as an exotic resembles
duction (Figure 8B,C,D). A. breviligulata main- that within its native range, with its vigor highly
tains a constant high cover value as the dune ma- dependent on sand deposition and with this de-
tures by replacing stands comprised of highly pendence manifesting itself in a series of succes-
vigorous and reproductive individuals with scat- sional changes reflecting a gradual decline in the
tered senescent plants interspersed in dense mats reproductive vigor of the stand and its constituent
of litter (Figure 8E and F). individual plants. This decline allows other spe-
This is typical of East Coast populations where cies to invade the senescing Ammophila com-
stands in areas with heavy deposition have high munity, increasing the species diversity (Figure
individual vigor with patchy distribution, and 9). This successional pattern of the west coast
those populations in stable or erosional areas have populations of A. breviligulata is analogous to the
a more even distribution of less vigorous plants growth phases described in the Great Lakes Re-
(DISRAELI, 1984). gion (ELDRED and MAUN, 1982; KRAJNYK and
Journal of Coastal Research, Vol. 10, No. 1, 1994
186 Seabloom and Wiedemann
0.8 0.8
0.7 0.7
x
0.6 S
C
-
0,
0.5
S0.4 C 0.4
0.6_
0.5
0 0
0.3
0.3
E E 0.2
0.2
0.1
0.1
0 0
Zone I Zone II Zone III Zone IV 4
3.5 3.5
Co
3 3
3
- 2.5
"O
C
ch
2.5
2
C 2
c-L
C 1.5
O 15 C
.C 1
0.5
0.5
Zone I Zone II Zone III Zone IV
0
Zone I Zone II Zone III A.
[III|| breviligulata ammophila
Zone IV
-A.
Figure 10. Comparison of the mean Simpson and Shannon
Figure 9. Comparison of the mean Simpson and Shannon Spe- Species Diversity Indices for the Ammophila breviligulata and
cies Diversity Indices of each of the four Dune Zones over the Ammophila arenaria populations in each of the four Dune Zones
total population of samples. Underlined Dune Zones are equiv- over the total population of samples. Underlined Dune Zones
alent at a = 0.05. are equivalent at a = 0.05.
MAUN, 1981), and in North Carolina (VAN DER sociated with each species was significantly dif-
VALK, 1975) with the exception of the location of ferent. The difference total crest height was the
the highest rates of sexual reproduction. only measure of dune shape which this study was
It is likely that the replacement of A. arenaria able to detect. However, the mean lengths of the
by A. breviligulata in the role of foredune colo- windward face of the two populations appear to
nizer had little effect on the overall species di- be quite different, and it is likely that the failure
versity. The only significant difference between to discern a difference in the length of the wind-
the A. breviligulata population and the A. ar- ward face represents a Type 1 error due to the
enaria population was in Zone II where both the limited availability of A. arenaria foredunes in
diversity indices showed that A. arenaria had a the study site (n = 6) (Table 1).
slightly higher diversity. It is likely that this is a The greater height of the A. arenaria dunes is
result of the prevalence of the A. arenaria/Lath- probably attributable to two factors. First, it has
yrus japonicus (maritime pea) association in this a higher sand trapping potential created by a
zone. L. japonicus is one of the few plant species higher stem density than A. breviligulata; and,
which can maintain a moderately high cover value secondly, its leaves are more persistent in the win-
in Ammophila dominated dunes, and it is not as ter due to their more erect growth and tighter
common in the A. breviligulata dominated dunes inrolling. The highest levels of sand movement
as it is in those dominated by A. arenaria. occur as a result of high winter winds (WIEDE-
Although there was little difference in species MANN, 1984), and the more persistent leaves of A.
diversity between the foredunes of the two Am- arenaria allows them to continue entrapping sand
mophila species, the shape of the foredune as- during this period when potential deposition is
Journal of Coastal Research, Vol. 10, No. 1, 1994
Ammophila breviligulata on the Washington Coast 187
Table 1. Comparisonof the means of three dune characters the Washington Department of Ecology; they were
of Ammophila breviligulata and Ammophila arenaria fore- utilized for the field supplies, aerial photographs,
dunes.
and travel expenses.
I would like to thank A. Wiedemann, as head
Signi-
ficant of my graduate committee for his interest, sup-
Ammophila Ammophila at a = port, and careful reviewing of this research from
Parameter breviligulata arenaria 0.01 inception to final draft. Additional thanks go to
Crest height 2.817 m 4.516 m Yes A. Greenberg, C. Harrington, C. Ivey, D. Miller,
Distance to crest 15.637 m 23.330 m No M. Witter, and L. Zemke for assistance in the
Slope (height: length) 0.261 0.259 No field.
LITERATURE CITED
the highest. A. breviligulata's leaves tend to die
back and become flattened into mats early in the BALDWIN, K. and MAUN,M.A., 1983. Microenvironment
of Lake Huronsand dunes. Canadian Journal of Bot-
winter where they are quickly buried by sand de-
any, 61, 241-255.
position. BARBOUR, M.G.; DEJONG, T.M., and JOHNSON, A.F., 1975.
Additionsand correctionsto a reviewof North Amer-
MANAGEMENT IMPLICATIONS ican Pacific Coast vegetation.Madrono, 23, 130-134.
BARBOUR,M.G.; DEJONG, T.M., and JOHNSON, A.F., 1976.
The conservation of native plant communities Synecologyof beachvegetationalongthe PacificCoast
is not affected differentially by either species to of the United States of America:A first approxima-
a degree which would warrant use in management tion. Journal of Biogeography,3, 55-69.
BARBOUR, M.G. and MAJOR, J., 1988. Terrestrial Veg-
strategies. Both species of Ammophila depress etation of California.CaliforniaNative Plant Society,
species diversity to a very high degree and are a Special Publication 9.
serious threat to the existence of diverse native J.E.
BROWER, and ZAR,J.H., 1977. Field and Laboratory
plant communities. However, the species' effects Methods for General Ecology. DuBuque, Iowa:Wm.
on dune shape do have management implications. C. Brown Publishers.
COWLES, H.C., 1899. The ecological relations of vege-
The difference in the shapes of the Ammophila tation of the sand dunes of Lake Michigan.Botanical
dunes affects structural and esthetic characters Gazette, 27, 95-117, 167-202, 281-308, 361-391.
of the foredune. The lower A. breviligulata dune DISRAELI, D.J., 1984.The effects of sand deposits on the
may be more susceptible to breaching during storm growthand morphologyof Ammophila breviligulata.
or flood events. If this is true, then the introduc- Journal of Ecology, 72, 145-154.
DUNLOP, D.A. and CROW,G.E., 1985. The vegetation
tion of A. breviligulata may have placed the coast- and floraof the Seabrookdunes with special reference
al communities of southern Washington at a high- to rare plants. Rhodora,87, 471-486.
er risk to flood or erosion damage. Conversely, ELDRED, R.A. and MAUN, M.A., 1982. A multi-variate
local residents may appreciate more visual access approachto the problem of decline in vigor of Am-
to the beach when their houses are located behind mophila breviligulata.Canadian Journal of Botany,
60, 1371-1380.
an A. breviligulata dune. This may result in a GLEASON, H.A. and CRONQUIST, A., 1963. Manual of
lowered incidence of illegal dune grading which VascularPlants of Northeastern United States and
immediately increases the risk of a damaging flood Adjacent Canada. Boston, Massachusetts: Willard
Grant Press.
event, and causes a funnelling of wind which can HITCHCOCK, A.S., 1950.AmmophilabreviligulataFern.,
cause weathering on neighboring structures. It may Americanbeachgrass.Manual of the Grasses of the
be that an unbreached A. breviligulata dune may United States. Washington,D.C.: U.S. Government
provide a better balance between protecting Printing Office.
coastal communities and allowing visual access to C.L.; CRONQUIST, A.; OWNBY, M., and
HITCHCOCK,
THOMPSON, J.W., 1969. VascularPlants of the Pacific
the beach than a tall dune which is regularly Northwest Part 1: Vascular Cryptograms, Gymno-
breached by illegal grading. sperms, and Monocotyledons. Seattle, Washington:
University of WashingtonPress.
ACKNOWLEDGEMENTS KRAJNYK, I.S. and MAUN, M.A., 1981. Vegetative re-
productionin the juvenile phase of Ammophila brevi-
The preparation of this report was financially ligulata. Canadian Journal of Botany, 59, 883-892.
aided with funds obtained from the National Oce- MAUN, M.A., 1984. Colonizing ability of Ammophila
anic and Atmospheric Administration, and ap- breviligulata through vegetative regeneration.Jour-
nal of Ecology, 72, 565-574.
propriated for the Coastal Zone Management Act MAUN, M.A. and BAYE,P.R., 1989. The Ecology of Am-
of 1972. D. Canning administered these funds for mophila breviligulataFern. on coastal dune systems.
Journalof CoastalResearch,Vol. 10, No. 1, 1994
188 Seabloomand Wiedemann
CRC Critical Reviews in Aquatic Sciences, 1, 661- zation in the Pacific Northwest, USA. International
681. Journal of Biometeorology, 21(3), 256-266.
OLSON, J.S., 1958a. Role of succession and soil changes SEABLOOM, E.W., 1991. Ecology and Distribution of
on Lake Michigan sand dunes. Botanical Gazette, Ammophila breviligulata Fern. (American beach-
119, 125-170. grass) on the Foredunes of the Washington Coast.
OLSON, J.S., 1958b. Lake Michigan dune development. MES Thesis, Olympia, Washington: The Evergreen
II. Plants as agents and tools of geomorphology. Jour- State College.
nal of Geology, 66, 345-351. VAN DER VALK, A.G., 1975. The floristic composition
PAVLIK, B.M., 1983. Nutrient and productivity relations and structure of fore-dune plant communities of Cape
of the dune grasses Ammophila arenaria and Elymus Hatteras National Seashore, North Carolina, USA.
mollis. 3. Spatial aspects of clonal expansion with Chesapeake Science, 16(2), 115-126.
reference to rhizome growth and dispersal of buds. WIEDEMANN, A.M., 1984. The Ecology of Pacific North-
Bulletin of the Torrey Botanical Club, 110, 271-279. west Coastal Sand Dunes: A Community Profile. U.S.
PHIPPS, J.B., 1990. Coastal Accretion and Erosion in Fish and Wildlife Service. FWS/OBS-84/04.
Southwest Washington: 1977-1987. Shorelands and WILLIS,A.J., 1963. Braunton Burrows: The effects on
Coastal Zone Management Program, Washington De- the vegetation of the addition of mineral nutrients to
partment of Ecology, Olympia. the dune soils. Journal of Ecology, 51, 353-374.
SCHWENDIMAN, J.L., 1977. Coastal sand dune stabili-
Journalof CoastalResearch,Vol. 10, No. 1, 1994
Foredunes of the Washington Coast
Author(s): E. W. Seabloom and A. M. Wiedemann
Source: Journal of Coastal Research, Vol. 10, No. 1 (Winter, 1994), pp. 178-188
Published by: Allen Press
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Journal of Coastal Research 1 10 1
1 178-188 1 Fort Lauderdale, Florida I Winter 1994
Distribution and Effects of Ammophila breviligulata Fern.
(American beachgrass) on the Foredunes of the Washington Coast
E.W. Seabloomt and A.M. Wiedemannt
tDepartment of Botany tThe Evergreen State College
353 Bessey Hall Olympia, WA 98505, U.S.A.
Iowa State University
Ames, IA 50011-1020, U.S.A.
ABSTRACT
SEABLOOM, E.W. and WIEDEMANN, A.M., 1994. Distribution and effects of Ammophila breviligulata
Fern. (American beachgrass) on the foredunes of the Washington coast. Journal of Coastal Research,
?? 10(1), 178-188. Fort Lauderdale (Florida), ISSN 0749-0208.
Since the turn of the century, the foredunes on the west coast of North America have become dominated
by Ammophila arenaria due to extensive sand stabilization plantings. Ammophila breviligulata was
planted less extensively than A. arenaria. However, A. breviligulata has come to singularly dominate the
foredunes of Washington in the southern half of the state and its range extends north along the entire
coast. By comparing the distribution of current A. breviligulata and A. arenaria communities with historic
shorelines, it was found that this invasion occurred in the last 50 years and the locus of the invasion was
determined. A comparison of foredunes dominated by A. breviligulata with existing A. arenaria foredunes
shows that this colonization has had minimal impact on the species diversity of the dunes, but it has
resulted in a lowering of the mean height of the foredune crests.
ADDITIONAL INDEX WORDS: Ammophila arenaria, dune morphology, introduced species, coastal
plant communities.
INTRODUCTION feature in the coastal ecosystem, replacing many
of the native communities in the foredune habitat
Ammophila breviligulata Fern. (American
beachgrass) is native to the East Coast and Great (PAVLIK,1983).
Lakes Region of North America (BALDWIN and Because of the overwhelming success of the A.
arenaria plantings, there has been little use of A.
MAUN, 1983; GLEASON and CRONQUIST, 1963;
OLSON, 1958a,b; HITCHCOCK, 1950; COWLES, 1899), breviligulata for dune stabilization on the west
and it has been intensively studied within this coast. Accordingly, very little information on the
native range (MAUN and BAYE, 1989). It is a pi- status of A. breviligulata on the west coast of
oneer species adapted to dynamic coastal dune North America is available. A review of this lit-
systems where it is, typically, the major dune erature and the collection history leads to the
building plant species present (DISRAELI, 1984; conclusion that A. breviligulata exists on the west
DUNLOP and CROW, 1985). It rapidly becomes se- coast only as persistent remnant populations
nescent when dune areas stabilize and is then (MAUN and BAYE, 1989; BARBOUR et al., 1975;
rapidly replaced by other species (DISRAELI,
1984; BARBOUR et al., 1976).
VAN DER VALK, 1975; ELDRED and MAUN, 1982). The only sizable planting of A. breviligulata
Ammophila arenaria (L.) Link (European that has been recorded was a part of the Warren-
beachgrass or marram grass) is a native of Europe ton Dunes Stabilization project on the Clatsop
similar to A. breviligulata in its adaptations to Peninsula in Oregon near the mouth of the Co-
the coastal dune ecosystems. A. arenaria has been lumbia River. The Soil Conservation Service un-
widely planted on the west coast of North America dertook this project in 1935; and up to that time,
for dune stabilization since the early 1900's. It has
it was one of the largest dune stabilization pro-
become naturalized along nearly the entire coast-
line (BARBOUR and MAJOR, 1988; HITCHCOCK et jects in the western United States. A nursery was
established at Warrenton, Oregon, and 1,214 ha
al., 1969; HITCHCOCK, 1950) and is a dominant
were progressively stabilized with a variety of spe-
cies including A. breviligulata (SCHWENDIMAN,
92133 received 25 November 1992; accepted in revision 27 March 1993. 1977). A. breviligulata from this nursery was also
Ammophila breviligulata on the Washington Coast 179
planted at the south end of the Long Beach Pen-
insula at Ilwaco (Figures 1, 2).
San Juan
At present, the densest populations of A. brevi- Archipelago
ligulata are located between the mouth of the Shi
Cape Flattery
Shi Beach Port
Columbia River and Westport, 75 km to the north.
Port Angeles
In this area, A. breviligulata is almost singularly
dominant on the foredune, the first dune land- Olympic
Peninsula
ward of the beach. The dominance of A. brevili- Seattle
gulata decreases beyond these boundaries to the Q Copalis River
north and south. This distribution pattern indi- o Grays Harbor Olympia
cates that the Clatsop and Ilwaco plantings were U Chehalis River
.H Willapal Ba
the likely source of the naturalized populations 4-4 Long Beac
-H Peninsula
of A. breviligulata now found on the Washington U
and Oregon coastal dunes.
The primary dispersal mechanism of A. brevi-
ligulata is through waterborne rhizome fragments
River
Washington
Columbia
(MAUN,1984), and the dominant current on the Sand Lake Oregon
southern Washington coast is the northward long-
North
shore current (PHIPPS, 1990). If the source of the
A. breviligulata invasion was the Clatsop and Il- 50 km
waco plantings, the longshore current would have LJ
rapidly spread rhizome fragments along the ac-
Figure 1. Map of the area surveyed for the distribution of
creting shoreline of the Long Beach Peninsula Ammophila breviligulata and Ammophila arenaria. The lo-
allowing A. breviligulata to colonize the beach cation of Figure 2 is shown as an inset.
and replace A. arenaria as the dominant dune
forming species.
If this scenario were the case, it should be pos-
sible to locate the transition from one Ammo- typical of prograding shorelines in this area. North
phila species to the other. Since both species of this point the rocky headlands are close to the
have extremely low vegetative and sexual repro- beach and prevent any major dune formation
ductive rates in stabilized dune areas (OLSON, (Figures 1 and 2).
1958a), it is unlikely that there would have been The objectives of this research were threefold:
significant invasion by either population in the to determine the source, location, and time period
highly stable backdune areas. WILLIS (1963) of the major introductions of the exotic species
found that even fertilization could not stimulate A. breviligulata; to establish the current range
senescent Ammophila populations to the point and habit of A. breviligulata on the Washington
of expansion. Coast; and to determine if the A. breviligulata
If there is no invasion in the backdune areas and A. arenaria foredunes differ significantly in
and the transition zone is stable, then the border structure or plant species diversity.
between the two communities actually represents METHODS
the location of the historic shoreline or foredune
crest when A. breviligulata replaced A. arenaria Study Sites
as the foredune's dominant grass. The quantitative fieldwork for the determina-
The timing of the introduction of A. brevili- tion of the source and timing of the introduction
gulata was determined by comparing the A. brev- of A. breviligulata and the characterization of the
iligulata/A. arenaria transition zone to the lo- current Ammophila dunes took place on the fore-
cation of historic foredunes as determined from dunes of the Washington Coast from North Head
a chronological sequence of aerial photos. The near the state's southern border at the mouth of
southern portion of the Washington coast is char- the Columbia River (460 17' 30" N Lat) north to
acterized by a broad band of sand beach and dunes Westport (460 52' 30" N Lat). In addition, the
as far north as the Copalis River (470 08' 00" N distribution of A. breviligulata was surveyed along
Lat). These dunes are examples of the parallel the western and northern coastlines of Washing-
dune system described by WIEDEMANN (1984) as ton as far east as Port Angeles and the north half
Journal of Coastal Research, Vol. 10, No. 1, 1994
180 Seabloom and Wiedemann
Field Sampling
Harbor
The quantitative fieldwork on dune shape and
Grays
105 vegetative characteristics was completed between
Westport July and October of 1988. A second series of 34
Twin Harbors
transects, 19 on the Long Beach Peninsula and
State Park o10 15 between Cape Shoalwater at the north edge of
the mouth of Willapa Bay and Westport, were
Cape
Shoalwater Willapa selected randomly. In addition, several transects
River
were established on the specific dunes where A.
Leadbetter
Point arenaria was dominant. None of these transects
coincided with those used for the historic shore-
line study.
illapa
Ocean Park ay The foredune profile was mapped by measuring
the height at 5 m intervals (survey stations) along
0)
u 103 a 50-75 m transect (depending on foredune width)
op
U running perpendicular to the foredune. This pro-
Long Beach 10 file was used to calculate the slope, length, and
Seaview
North Head Ilwaco
height of the west face of the foredune. The tran-
sect started at the lower limit of the vegetation.
Columbia
River This point was given an arbitrary elevation of zero
Clatsop, Spit -~
m. The dune crest height was measured indepen-
Warrenton * 30
dently, if it did not coincide with one of the survey
stations. In addition, the following data were col-
North lected at these survey stations within a 20 by 50
25 km1 cm rectangular quadrat placed perpendicular to
the transect line and centered on each survey stake:
Figure 2. Map of the Long Beach Peninsula, and the site of
the quantitative dune morphology and population studies. (a) the total number shoots of each species of
Ammophila in the quadrat; (b) The width of the
second lowest live leaf at a point 2 cm distal from
of the coast of Oregon as far south as Sand Lake the ligule on the culm nearest the southeast corner
(Figures 1 and 2). of the quadrat; (c) the number of Ammophila
inflorescences in the quadrat; and (d) the % cover
The Introduction of A. breviligulata
(using the 1-10 Domin Cover Class scale) within
The localization of the A. breviligulatalA. ar- the quadrat of all plant species, vegetative litter,
enaria transition zone on the Long Beach Pen- and bare ground.
insula at 17 transects was mapped onto a 1:12,000 A. breviligulata and A. arenaria generally oc-
scale aerial photograph series taken on 31 July curred in discrete stands, and were readily dis-
1988, one month prior to the time the measure- tinguishable in the field on the basis of ligule
ments were taken. Initially, 21 transect locations length, inflorescence morphology, phenology, and
were chosen at one mile intervals beginning at the foliar characteristics (SEABLOOM, 1991). Speci-
Seaview beach access and running north to Lead- mens of both species from a number of represen-
better Point, however, four locations were elimi- tative locations in Washington and Oregon were
nated due to human disturbances in the backdune deposited in the University of Washington Her-
area. barium, Seattle, Washington.
The historic foredune position was determined Because the transect profiles varied widely, each
using a series of historic aerial photos (1949, 1964, transect was divided into four habitat zones to
1970, 1974, and 1982). The location of the fore- facilitate comparative analysis (Figure 4). This
dune for each of these years was determined at zonal approach permits the comparison of the dis-
each transect and mapped onto the 1988 photo tinct environments present on each foredune by
series. It was then possible to measure the dis- correcting for the specific profile of each foredune.
tance to the east or west that each historic dune The beach (Zone I) extends from the seaward line
lay from the A. breviligulatalA. arenaria tran- of vegetation east to the seaward toe of the dune;
sition zone (Figure 3). the windward slope (Zone II) extends from this
Journal of Coastal Research, Vol. 10, No. 1, 1994
Ammophila breviligulata on the Washington Coast 181
A. breviligulata A. arenaria
30
S* 1941
a 1964
S* 1970
v 1974
0 25 o 1981
. 1988
C,)
o
4-
.~- 20
0
z
E S
15
10
5
400 300 200 100 100 200 30 400
Meters West of Transition Meters East of Transition
Figure 3. Location of the transition between the Ammophila breviligulata and Ammophila arenaria communities in relation to
the locations of six historic foredunes on the Long Beach Peninsula.
Journal of Coastal Research, Vol. 10, No. 1, 1994
182 Seabloom and Wiedemann
Beach I Windward Slope I Leeward Slope I Backdune
I i
est
Figure 4. Four Zones of the coastal foredune.
point to just past the crest of the foredune; The North Head at the southern end of the Long Beach
leeward slope (Zone III) extends from the limit Peninsula to Westport, where it is present in near-
of high sand accretion just past the foredune crest ly monospecific stands in Zones II, III, and IV
to the landward toe of the dune; and the backdune (Figures 1 and 5). On the dune systems north of
(Zone IV) includes all of the area east this point. Westport both species of Ammophila alternate as
The vegetative and dune profile data were com- the dominant foredune species. The only sizable
pared between dune zones using an ANOVA fol- unmixed A. arenaria foredune community locat-
lowed by a Fisher's Test for Least Significant Dif- ed in Washington was at Twin Harbors State Park
ferences to locate the sources of the detected south of Westport where five acres was planted
variance. An ANOVA was also used to compare in 1981 as part of a cooperative project between
A. breviligulata and A. arenaria populations. The the Soil Conservation Service and the Washing-
Simpson and Shannon indices were used to com- ton Parks and Recreation Commission. This pop-
pare species diversity between dune zones and ulation now covers about 3 km of coastline.
Ammophila communities (BROWER and ZAR, The second niche A. breviligulata occupies is
1977). the area between the shoreward toe of the fore-
RESULTS dune and the lower limit of vegetation (Zone I).
In this area, it creates hummocks, usually less
The Introduction of A. breviligulata than 2 m in diameter, along with a number of
In 0.76 of the transects, the transition between native hummock forming species, including Am-
A. breviligulata and A. arenaria dominated stands brosia chamissonis (silver bursage), Cakile eden-
occurred between the location of the 1964 and the tula (American searocket), and Abronia latifolia
1974 or the 1970 and 1974 shorelines. In all but (yellow sand-verbena).
one transect, the transition zone was bounded by In this more marginal habitat, A. breviligulata
the 1941 and the 1974 shorelines. This one vari- can be found along the entire Washington coast
ation occurred because there was no information as far north as Shi Shi Beach and south to Sand
available prior to 1964 at that location (Figure 3). Lake in Oregon, although its frequency decreases
markedly at the northern and southern limits of
Current Range and Habit of A. breviligulata this range. A. breviligulata can also be found scat-
Within its current range on the west coast, A. tered on sand bars and spits in Willapa Bay and
breviligulata occupies two distinct habitats. First, Grays Harbor, although this habitat is dominated
it is the dominant vegetation on the foredunes in by the native Elymus mollis (American dune-
the quantitative study area which ranges from grass) (Figure 1).
Journal of Coastal Research, Vol. 10, No. 1, 1994
Ammophila breviligulata on the Washington Coast 183
6 4
5 a, 33
CO
4 O
LL 2
0
3 0. 1
C
E 2 0
0 35
E
( 30
0
LL 25
c 20
Zone I Zone II Zone III Zone IV
A. breviligulata
III|||I| A. arenaria
8 10
Figure 5. Comparison of the dominance of Ammophila brevi- a
ligulata and Ammophila arenaria in each of the four Dune 0
Zones as indicated by their respective cover of live plants av- 0.5
eraged over the entire population of samples.
au
LL
0.4 -
5 0.3
Neither species of Ammophila was located along 0
0.2
o
the northern edge of the Olympic Peninsula, but a-
o 0.1
A. breviligulata is present at Port Townsend and
both A. breviligulata and A. arenaria are present 0
in the San Juan Archipelago (Figure 1). North Central South
Field observations of the A. breviligulata pop- Figure 6. Comparison of the mean height, slope, and length
ulation on the Long Beach Peninsula distin- of the west face of the foredunes in the three Geographic Units
on the Long Beach Peninsula.
guished three distinct geographic units on the ba-
sis of dune shape and vegetative characteristics.
The South Unit extends from North Head to Long
Beach and is characterized by a low foredune with the plant communities in these three Units was
minimally developed beach plant communities not found to be significantly different (Figure 7).
characterized by Cakile edentula. The Central The percent cover of live A. breviligulata plants
Unit extends from Long Beach, north to Ocean and vegetative litter increases markedly from the
Park and has a low A. breviligulata foredune beach to the dune, but remains constant on the
somewhat similar to the southern Unit; however, entire foredune (Figure 8A,F). Stem density
Zone I in this Unit has a well developed vegetative reaches its maximum on the seaward slope of the
community dominated by Ambrosia chamissonis dune in Zone II (Figure 8B) and flowering occurs
with Cakile edentula and Abronia latifolia as as- almost entirely in Zone I (Figure 8C). Leaf width
sociated species. The North Unit extends from also appears to be an indicator of the vigor of the
Ocean Park north to Leadbetter Point and has a individual plants since it diminishes steadily with
steep foredune of A. breviligulata with little or increasing distance from the beach. The width
no beach vegetation (Figure 2). remains equivalent in Zones I and II but drops
An ANOVA comparison of these three geo- consecutively in Zone III and again in Zone IV
graphic units showed that their foredunes differed (Figure 8D). The presence of bare ground in the
significantly in height of the crest, length of the transects drops as {he cover value of A. brevili-
windward face, and slope of the windward face. gulata increases and the individual vigor of the
In all three parameters, the only equivalency was plants is declining (Figure 8E).
between the height of the dunes in the South and This decrease in the vigor of the Ammophila
Central Units (Figure 6). The species diversity of stands was paralleled by an increase in species
Journal of Coastal Research, Vol. 10, No. 1, 1994
184 Seabloom and Wiedemann
within a stand rather than the importance of the
0.8
species in the study area as a whole. The stem
density was significantly (P = 0.012) greater for
0.7 A. arenaria (203 stems/m2) than for A. brevili-
x o.s gulata (79 stems/m2).
0.4 Comparing the means of the three dune shape
parameters for the entire population of foredunes
r 0.4 showed that the population of A. arenaria dunes,
0
a 0.3
E
which had a mean elevation of 4.52 m, were sig-
0.2 nificantly taller than the A. breviligulata dune
0.1
which had an overall mean of 2.82 m. However,
while the A. breviligulata dunes were only 67%
0
as long as the A. arenaria dunes, the ANOVA
3.5 failed to detect a difference between the two pop-
ulations (P = 0.147). The slope of the windward
x face of the dunes associated with both species of
2.5 Ammophila was nearly identical and there was
2-
no difference detected in the ANOVA (Table 1).
0
o 1.s
DISCUSSION AND CONCLUSIONS
c
The current locus of A. breviligulata on the
west coast supports the conclusion that the col-
0.5
onization source was the Clatsop and Ilwaco
0 plantings which began in 1935. This conclusion is
Zone I Zone II Zone III Zone IV
in accord with the timing of the colonization of
NorthUnit - CentralUnit %South Unit the Long Beach Peninsula foredunes as deter-
IIIIIIl
mined by examining the distribution of A. brevi-
Figure 7. Comparison of the Simpson and Shannon Species
Diversity Indices of each of the four Dune Zones between the ligulata and A. arenaria in relation to the location
three Geographic Units on the Long Beach Peninsula. of historic shorelines. These findings indicate that
A. breviligulata replaced A. arenaria as the pri-
mary foredune colonizing species between 1941
and 1974, and it is most likely that the majority
diversity in the stable backdune areas as com- of the colonization occurred in the ten year period
pared to the high depositional environment of from 1964 to 1974 (Figure 3).
Zones I and II (Figure 9). The maximum stem density in Washington
populations (Figure 8B) occurs in a similar suc-
Comparison of A. breviligulata and A. arenaria cessional stage and within the range of values giv-
Foredunes en for stands along Lake Michigan, which range
A comparison of the foredune communities from 110 to 150 stems/m2 and the cover values of
dominated by A. breviligulata versus those dom- 50 to 59% (KRAJNYK and MAUN, 1981; OLSON,
inated by A. arenaria showed equivalent species 1958a). However, flowering occurs almost entirely
diversity indices in all the Zones except Zone II in Zone I in Washington (Figure 8C) while on
(Figure 10). In this Zone, A. arenaria foredune Lake Erie flowering reaches its peak in the ado-
communities have a slightly higher species diver- lescent growth phase when stem density is the
sity than the A. breviligulata dominated fore- highest (KRAJNYK and MAUN, 1981). This is
dunes. Both the Simpson and the Shannon in- equivalent to Zone II where the flowering rates
dices show this difference at the same confidence were low for the Washington populations (Figure
level. 8C).
The overall stem density between the Am- While the overall % cover of A. breviligulata
mophila species was compared over the entire set shows a marked increase from the beach to the
of samples. All of the samples with density values dune, the cover values remain relatively constant
of zero were excluded from this comparison. This on the foredune proper in Zones II, III, and IV
was done in order to compare mean stem density (Figure 8A). However, the vigor of the individual
Journal of Coastal Research, Vol. 10, No. 1, 1994
Ammophila breviligulata on the Washington Coast 185
7
n C6
A. 120 B.
E8o
,- 3 E 60
-2 0 40
a)
o1 20
0 0
I II III IV I II III IV
35
-14
30 -12
E
Cq25 E
Ilo
E20 8
0 8
I II III IV I II III IV
12 10
o
015
E. 9F.
8
a)2
(.8 7
0 - 7
0)6
>2 0510
0 0 0
I II III IV I II III IV
Geographic Zone Geographic Zone
Figure 8. Comparison of six indicators of Ammophila breviligulata population vigor between each of the four Dune Zones throughout
the entire set of transects. Total cover of live plants, stem density, flower shoot density, leaf width, cover of bare ground, and cover
of litter are shown as graphs A-F respectively. Underlined Dune Zones are equivalent at a = 0.05.
plants diminishes as indicated by decreasing leaf Thus, the overall ecology of A. breviligulata on
width and depressed vegetative and sexual repro- the west coast in its range as an exotic resembles
duction (Figure 8B,C,D). A. breviligulata main- that within its native range, with its vigor highly
tains a constant high cover value as the dune ma- dependent on sand deposition and with this de-
tures by replacing stands comprised of highly pendence manifesting itself in a series of succes-
vigorous and reproductive individuals with scat- sional changes reflecting a gradual decline in the
tered senescent plants interspersed in dense mats reproductive vigor of the stand and its constituent
of litter (Figure 8E and F). individual plants. This decline allows other spe-
This is typical of East Coast populations where cies to invade the senescing Ammophila com-
stands in areas with heavy deposition have high munity, increasing the species diversity (Figure
individual vigor with patchy distribution, and 9). This successional pattern of the west coast
those populations in stable or erosional areas have populations of A. breviligulata is analogous to the
a more even distribution of less vigorous plants growth phases described in the Great Lakes Re-
(DISRAELI, 1984). gion (ELDRED and MAUN, 1982; KRAJNYK and
Journal of Coastal Research, Vol. 10, No. 1, 1994
186 Seabloom and Wiedemann
0.8 0.8
0.7 0.7
x
0.6 S
C
-
0,
0.5
S0.4 C 0.4
0.6_
0.5
0 0
0.3
0.3
E E 0.2
0.2
0.1
0.1
0 0
Zone I Zone II Zone III Zone IV 4
3.5 3.5
Co
3 3
3
- 2.5
"O
C
ch
2.5
2
C 2
c-L
C 1.5
O 15 C
.C 1
0.5
0.5
Zone I Zone II Zone III Zone IV
0
Zone I Zone II Zone III A.
[III|| breviligulata ammophila
Zone IV
-A.
Figure 10. Comparison of the mean Simpson and Shannon
Figure 9. Comparison of the mean Simpson and Shannon Spe- Species Diversity Indices for the Ammophila breviligulata and
cies Diversity Indices of each of the four Dune Zones over the Ammophila arenaria populations in each of the four Dune Zones
total population of samples. Underlined Dune Zones are equiv- over the total population of samples. Underlined Dune Zones
alent at a = 0.05. are equivalent at a = 0.05.
MAUN, 1981), and in North Carolina (VAN DER sociated with each species was significantly dif-
VALK, 1975) with the exception of the location of ferent. The difference total crest height was the
the highest rates of sexual reproduction. only measure of dune shape which this study was
It is likely that the replacement of A. arenaria able to detect. However, the mean lengths of the
by A. breviligulata in the role of foredune colo- windward face of the two populations appear to
nizer had little effect on the overall species di- be quite different, and it is likely that the failure
versity. The only significant difference between to discern a difference in the length of the wind-
the A. breviligulata population and the A. ar- ward face represents a Type 1 error due to the
enaria population was in Zone II where both the limited availability of A. arenaria foredunes in
diversity indices showed that A. arenaria had a the study site (n = 6) (Table 1).
slightly higher diversity. It is likely that this is a The greater height of the A. arenaria dunes is
result of the prevalence of the A. arenaria/Lath- probably attributable to two factors. First, it has
yrus japonicus (maritime pea) association in this a higher sand trapping potential created by a
zone. L. japonicus is one of the few plant species higher stem density than A. breviligulata; and,
which can maintain a moderately high cover value secondly, its leaves are more persistent in the win-
in Ammophila dominated dunes, and it is not as ter due to their more erect growth and tighter
common in the A. breviligulata dominated dunes inrolling. The highest levels of sand movement
as it is in those dominated by A. arenaria. occur as a result of high winter winds (WIEDE-
Although there was little difference in species MANN, 1984), and the more persistent leaves of A.
diversity between the foredunes of the two Am- arenaria allows them to continue entrapping sand
mophila species, the shape of the foredune as- during this period when potential deposition is
Journal of Coastal Research, Vol. 10, No. 1, 1994
Ammophila breviligulata on the Washington Coast 187
Table 1. Comparisonof the means of three dune characters the Washington Department of Ecology; they were
of Ammophila breviligulata and Ammophila arenaria fore- utilized for the field supplies, aerial photographs,
dunes.
and travel expenses.
I would like to thank A. Wiedemann, as head
Signi-
ficant of my graduate committee for his interest, sup-
Ammophila Ammophila at a = port, and careful reviewing of this research from
Parameter breviligulata arenaria 0.01 inception to final draft. Additional thanks go to
Crest height 2.817 m 4.516 m Yes A. Greenberg, C. Harrington, C. Ivey, D. Miller,
Distance to crest 15.637 m 23.330 m No M. Witter, and L. Zemke for assistance in the
Slope (height: length) 0.261 0.259 No field.
LITERATURE CITED
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productionin the juvenile phase of Ammophila brevi-
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