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Distribution and Invasion Potential of Limonium ramosissimum subsp. provinciale in San Francisco Estuary Salt Marshes

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Non-native sea lavenders (Limonium spp.) are invasive in salt marshes of southern California and were first documented in the San Francisco Estuary (the estuary) in 2007. In this study, we mapped distributions of L. ramosissimum subsp. provinciale (LIRA) and L. duriusculum within the estuary and investigated how the invasion potential of the more common species, LIRA, varies with elevation and edaphic conditions. We contacted colleagues and conducted field searches to find and then map sea lavender populations. In addition, we measured LIRA's elevational range at three salt marshes. Across this range we measured (1) soil properties: salinity, moisture, bulk density, and texture; and (2) indicators of invasion potential: LIRA size, seed production, percent cover, spread (over 1year), recruitment, and competition with native halophytes (over 6 months). We found LIRA in 15,144 m2 of upper salt marsh habitat in central and south San Francisco bays andL. duriusculum in 511 m2 in Richardson and San Pablo bays. LIRA was distributed from mean high water (MHW) to 0.42 m above mean higher high water (MHHW). In both spring and summer, soil moisture and salinity were lowest at higher elevations within LIRA's range, which corresponded with greater rosette size, inflorescence and seed production (up to 17,400 seeds per plant), percent cover, and recruitment. LIRA cover increased on average by 11% in 1year across marshes and elevations. Cover of the native halophytes Salicornia pacifica, Jaumea carnosa, and Distichlis spicata declined significantly at all elevations if LIRA were present in plots (over a 6-month, fall-winter period). Results suggest LIRA's invasion potential is highest above MHHW where salinity and moisture are lower, but that LIRA competes with native plants from MHW to above MHHW. We recommend removal efforts with emphasis on the salt marsh-terrestrial ecotone where LIRA seed output is highest.
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Title:
Distribution and Invasion Potential of Limonium ramosissimum subsp. provinciale in San Francisco
Estuary Salt Marshes
Journal Issue:
San Francisco Estuary and Watershed Science, 12(2)
Author:
Archbald, Gavin, H. T. Harvey & Associates (current)
Boyer, Katharyn E., Romberg Tiburon Center and Department of Biology, San Francisco State
University
Publication Date:
2014
Publication Info:
San Francisco Estuary and Watershed Science
Permalink:
http://escholarship.org/uc/item/61v8r7zw
Acknowledgements:
Funding was provided by the San Francisco State Department of Biology (including the Mentorship
in Quantitative Biology Program, NSF Grant No. EF-046313), and College of Science and
Engineering, the ARCS Foundation, the South Bay Salt Ponds Restoration Project, Northern
California Botanists, the Association for Environmental Professionals, and the Romberg Tiburon
Center for Environmental Studies and the Graduate Mentorship in Quantitative Biology Program.
We thank T. Parker, M. Page, and P. Baye for comments that improved earlier versions of the
manuscript, and staff of the California State Coastal Conservancy’s Invasive Spartina Project for
helping to identify invasion locations. Site access was provided by the Don Edwards National
Wildlife Refuge, the City of Burlingame, and the County of San Mateo Parks and Recreation.
Author Bio:
Associate Professor of Biology
Keywords:
Distichlis, edaphic, invasion,Jaumea, Limonium, moisture, salt marsh-terrestrial ecotone, salinity,
Salicornia, Grindelia, Ecology, Restoration Ecology, Invasion Ecology, Salt Marsh Ecology
Local Identifier:
jmie_sfews_18824
eScholarship provides open access, scholarly publishing
services to the University of California and delivers a dynamic
research platform to scholars worldwide.
Abstract:
Non-native sea lavenders (Limonium spp.) are invasive in salt marshes of southern California
and were first documented in the San Francisco Estuary (the estuary) in 2007. In this study, we
mapped distributions of L. ramosissimum subsp. provinciale (LIRA) and L. duriusculum within the
estuary and investigated how the invasion potential of the more common species, LIRA, varies
with elevation and edaphic conditions. We contacted colleagues and conducted field searches to
find and then map sea lavender populations. In addition, we measured LIRA’s elevational range
at three salt marshes. Across this range we measured (1) soil properties: salinity, moisture, bulk
density, and texture; and (2) indicators of invasion potential: LIRA size, seed production, percent
cover, spread (over 1 year), recruitment, and competition with native halophytes (over 6 months).
We found LIRA in 15,144 m
2
of upper salt marsh habitat in central and south San Francisco
bays and L. duriusculum in 511 m
2
in Richardson and San Pablo bays. LIRA was distributed from
mean high water (MHW) to 0.42 m above mean higher high water (MHHW). In both spring and
summer, soil moisture and salinity were lowest at higher elevations within LIRA’s range, which
corresponded with greater rosette size, inflorescence and seed production (up to 17,400 seeds per
plant), percent cover, and recruitment. LIRA cover increased on average by 11% in 1 year across
marshes and elevations. Cover of the native halophytes Salicornia pacifica, Jaumea carnosa,
and Distichlis spicata declined significantly at all elevations if LIRA were present in plots (over a
6-month, fall–winter period). Results suggest LIRA’s invasion potential is highest above MHHW
where salinity and moisture are lower, but that LIRA competes with native plants from MHW to
above MHHW. We recommend removal efforts with emphasis on the salt marsh-terrestrial ecotone
where LIRA seed output is highest.
Supporting material:
Appendix A: Additional Figures to Describe Distribution and Invasion Potential of LIRA in SF
Estuary Salt Marshes
Appendix B: Tables of Statistics to Describe Distribution and Invasion Potential of LIRA in SF
Estuary Salt Marshes
Copyright Information:
Copyright 2014 by the article author(s). This work is made available under the terms of the Creative
Commons Attribution3.0 license, http://creativecommons.org/licenses/by/3.0/
JUNE 2014
Distribution and Invasion Potential
of Limonium ramosissimum subsp. provinciale
in San Francisco Estuary Salt Marshes
Gavin Archbald
1,
*
and Katharyn E. Boyer
1
ABSTRACT
Non-native sea lavenders (Limonium spp.) are
invasive in salt marshes of southern California and
were first documented in the San Francisco Estuary
(the estuary) in 2007. In this study, we mapped
distributions of L. ramosissimum subsp. provinciale
(LIRA) and L. duriusculum within the estuary and
investigated how the invasion potential of the more
common species, LIRA, varies with elevation and
edaphic conditions. We contacted colleagues and
conducted field searches to find and then map sea
lavender populations. In addition, we measured
LIRA’s elevational range at three salt marshes. Across
this range we measured (1) soil properties: salinity,
moisture, bulk density, and texture; and (2) indicators
of invasion potential: LIRA size, seed production,
percent cover, spread (over 1 year), recruitment, and
competition with native halophytes (over 6 months).
We found LIRA in 15,144 m
2
of upper salt marsh
habitat in central and south San Francisco bays and
L. duriusculum in 511 m
2
in Richardson and San
Pablo bays. LIRA was distributed from mean high
water (MHW) to 0.42 m above mean higher high
water (MHHW). In both spring and summer, soil
moisture and salinity were lowest at higher elevations
within LIRA’s range, which corresponded with greater
rosette size, inflorescence and seed production
(up to 17,400 seeds per plant), percent cover, and
recruitment. LIRA cover increased on average by
11% in 1 year across marshes and elevations. Cover
of the native halophytes Salicornia pacifica, Jaumea
carnosa, and Distichlis spicata declined significantly
at all elevations if LIRA were present in plots (over
a 6-month, fall–winter period). Results suggest
LIRA’s invasion potential is highest above MHHW
where salinity and moisture are lower, but that
LIRA competes with native plants from MHW to
above MHHW. We recommend removal efforts with
emphasis on the salt marsh-terrestrial ecotone where
LIRA seed output is highest.
1 Romberg Tiburon Center for Environmental Studies and Department
of Biology, San Francisco State University, San Francisco, CA USA
* Corresponding author and current affiliation:
H. T. Harvey & Associates, Los Gatos, CA USA
gavinarchbald@gmail.com
SAN FRANCISCO ESTUARY & WATERSHED SCIENCE
2
INTRODUCTION
Invasive plants can be harmful to native species and
ecosystem functions (Vitousek et al. 1997; D’Antonio
et al. 2004), making early identification, assessment,
and response to new plant invasions important for
ecosystem management (Chornesky and Randall
2003; Ielmini and Ramos 2003). In the San Francisco
Estuary (hereafter, the estuary) tidal marshes, invasive
plants have spread aggressively (e.g., Spartina alter-
niflora × foliosa and Lepidium latifolium), displacing
native species and their associated functions (Goals
Project 1999; Levin et al. 2006; Boyer and Burdick
2010). As new non-native plant species establish, it is
important to understand their ecology and potential
for spread so that resources may be prioritized toward
controlling species that pose the greatest threat. To
this end, land managers and scientists recommend
describing the current spatial extent of introduced
species and evaluating how invasion potential is
influenced by abiotic environmental factors that vary
across landscapes (Grossinger et al. 1998; Byers et al.
2002; Robison 2009).
A single Limonium (sea lavender) species, L. califor-
nicum (marsh rosemary) is native to the estuary and
is found in salt and brackish upper marsh habitats
throughout most of coastal California (Baldwin et
al. 2012). The Limonium genus, however, is cos-
mopolitan and includes a number of low growing,
rosette-forming, perennial halophytic forbs native
to sea-lavender steppe communities in western
Mediterranean coastal salt marshes, maritime cliffs,
and saline dunal depressions (Devillers–Terschuren
and Devillers–Terschuren 2001). Several of these,
including L. ramosissimum (Algerian sea lavender),
L. duriusculum (no common name) and L. biner-
vosum (rock sea lavender) have invaded estuarine
wetlands on the West Coast of North America from
Santa Barbara County south into Baja California
(Barbour et al. 2007; COCH c2007). These species
were likely introduced through the horticultural trade
(Hubbard and Page 1997), and L. ramosissimum and
L. duriusculum are highly invasive in salt marsh hab-
itats in central and southern California (Hubbard and
Page 1997; 2012 email from J. Sayers to G. Archbald,
unreferenced, see “Notes").
Recently, Limonium ramosissimum subsp. provin-
ciale
1
(hereafter LIRA) and L. duriusculum (hereafter
LIDU) have been observed above and below the high
tide line in estuary marshes (Baye 2008) (Figure 1).
In spring of 2007, LIDU was discovered growing in
dense patches in Strawberry Marsh, (Marin County,
CA) in Richardson Bay (K. Boyer, pers. obs., 2007;
email from A. Ryan to G. Archbald, unreferenced,
see "Notes"). Later in 2007, LIRA was found growing
densely at Sanchez Creek Marsh (San Mateo County,
CA) and in multiple neighboring marshes, raising
concern that both species could be widespread in the
estuary. LIRA has simple, oblanceolate–spathulate
leaves (80 to 100 mm × 15 to 20 mm, L×W) that
form a basal rosette and annually produces branching
inflorescences (30 to 50 cm) opening into flowered
spikelets with purple corollas. LIDU has oblanceolate-
spathulate, obtuse to truncate leaves (30 to 40 mm ×
5 to 9 mm) and inflorescences similar to LIRA (Tutin
1964). LIRA and LIDU may have been mistaken for
L. californicum in the estuary and thereby overlooked
for a decade or more. In fact, LIRA was accidentally
planted during at least one marsh restoration proj-
ect in San Francisco in the 2000s (2010 in-person
conversation between P. Baye and K. Boyer, unref-
erenced, see "Notes") and seeded at several restored
marshes in the South San Francisco Bay region of the
estuary (2012 email from D. Thomson to G. Archbald,
unreferenced, see "Notes"). These events emphasize
1 In spite of comprehensive treatment of the genus Limonium by Tutin
et al. (1964), Erben (1993), and Arrigoni and Diana (1993), taxonomic
and nomenclatural issues in the genus remain unresolved. This is,
in part, because there are many species of Limonium with similar
morphological traits, and it is difficult to access European herbaria
specimens for comparison with species found in California. Botanical
samples from Sanchez Creek Marsh (Burlingame, CA) and Seal Slough
(Foster City, CA) study sites were examined by D. Kelch, California
Departure of Food and Agriculture, and submitted to California her-
baria under the name L. ramosissimum subsp. provinciale; however,
these specimens also keyed well to L. binervosum (2012a email from
D. Kelch to G. Archbald, unreferenced, see “Notes"). While the name
L. ramosissimum subsp. provinciale is accepted in the Flora Europaea
(Tutin et al. 2001) and the United States Department of Agriculture
Plants Database (USDA [mod 2014]), the Jepson Flora Project (c2014)
considers L. ramosissimum subsp. provinciale unresolved and it may
be synonymous with L. ramosissimum.
JUNE 2014
3
estuary (2012 email from D. Thomson to G. Archbald,
unreferenced, see "Notes"). These events emphasize
the need to document and increase awareness of
Limonium species in estuary marshes.
LIRA and LIDU may threaten plant and vertebrate
diversity in high salt marsh and marsh–terrestrial
ecotone habitats (hereafter, the transition zone). Both
habitats have been severely reduced from human
activities in estuary tidal marshes (Collins and
Grossinger 2004), yet still support high species rich-
ness relative to the marsh plain. Historically, these
habitats contained a suite of plant species that are
now rare and subject to conservation and restoration
measures, including Chloropyron maritimum subsp.
palustre (Point Reyes bird’s beak), Suaeda californica
(California sea-blight), Elymus triticoides (creeping
wild rye), Ambrosia psilostachya (western ragweed),
and Carex praegracilis (field sedge) (Josselyn 1983;
Baye et al. 2000; Boyer and Thornton 2012). In addi-
tion, upper marsh habitats are important for endan-
gered vertebrates, including Rallus longirostris obso-
letus (California clapper rail) and Reithrodontomys
raviventris (salt marsh harvest mouse), which rely on
canopies of Grindelia stricta (gumplant), Salicornia
pacifica (perennial pickleweed), and Distichlis spicata
(saltgrass) either for nesting or refuge from predators,
particularly during extreme high tide events (Josselyn
1983; SFBBO [cited 2013]). If LIRA or LIDU replace
these native plants, the resulting vegetation structure
dominated by short basal rosettes is unlikely to pro-
vide effective cover from predators.
Concern about the possible effects of invasive
Limonium in the estuary has prompted research to
detect it via remote sensing (Archbald 2010a), studies
to understand how anthropogenic changes influence
its spread (Cleave 2012), and removal efforts (e.g., by
the Bay Area Early Detection Network, Richardson
Bay Audubon Center and Sanctuary, and San
Francisco State University classes). Decisions on how
and where to manage this invasion require an under-
standing of the patterns of abundance and distribu-
tion of introduced sea lavenders within and among
estuary marshes.
Both abiotic conditions and competition are impor-
tant factors that structure salt marsh plant species
assemblages, and both likely influence the potential
for invasion by introduced Limonium species. Driven
Figure 1 Invasive sea lavender in San Francisco Estuary marshes: (A.) Limonium duriusculum, (B.) Limonium ramosissimum subsp.
provinciale. Photos by G. Archbald.
SAN FRANCISCO ESTUARY & WATERSHED SCIENCE
4
Hedel 1976; Zedler 1982), variation in physical stress
associated with salinity and moisture strongly influ-
ences species distributions in salt marshes (Chapman
1934; Hinde 1954; Bertness and Ellison 1987; Kuhn
and Zedler 1997; Cantero et al. 1998; Crowl et al.
2008). Where abiotic stress is high (e.g., via hypersa-
linity, anaerobic conditions or extreme desiccation),
plant species able to tolerate harsh environmental
conditions succeed. But where abiotic stress is low
(e.g., conditions of low salinity or moderate mois-
ture), marsh halophytes often grow taller, and/or
produce more seed (Seliskar 1985; Schile et al. 2011;
Ryan and Boyer 2012) and interspecific competition
may become a more important factor structuring
marsh communities (Pennings and Callaway 1992;
Crain et al. 2004).
In the estuary, our preliminary observations of intro-
duced sea lavenders suggest they grow most vigor-
ously at higher elevations in the upper high marsh
and into the transition zone, which could result from
a reduction in moisture, salinity, or other stressors.
Previous studies in the region have found salinity to
decline with elevation through the transition zone.
For example, in San Pablo Bay (northern estuary),
Mahall and Park (1976) found that maximum salin-
ity occurred just above MHW (which corresponded
in their study within the pickleweed plain) and
decreased landward, regardless of season. Similarly,
Traut (2005) found soil salinity decreased from the
pickleweed dominated mid-marsh through the transi-
tion zone in Pt. Reyes National Seashore (50 km N of
the estuary).
The effects of soil conditions on introduced sea
lavenders in the estuary have not been evaluated,
but another study found Limonium vulgare was
inhibited by high inundation and salinity (Boorman
1971). Further, in Carpinteria Salt Marsh (near Santa
Barbara, California) LIDU
2
was found to grow from
the upper edge of the marsh plain, dominated by
2 Hubbard and Page (2007) tentatively identified the invasive sea lav-
ender in Carpinteria salt marsh as L. ramosissimum, but the plant was
later identified as L. duriusculum (2012b email from D. Kelch to G.
Archbald, unreferenced, see “Notes").
S. pacifica to the upper reach of tides (0.8 to 1.4 m
above mean sea level [msl]) (Hubbard and Page
1997). In that warm, dry region, hypersalinity devel-
ops in summer with increasing elevation (Callaway
et al. 1990), and LIDU grew largest, had the highest
cover (up to 75%), and outcompeted native peren-
nial halophytes in the lower portion of its range
where soil moisture and salinity were more moder-
ate (Hubbard and Page 1997). We predicted a similar
improvement in introduced Limonium performance
in the estuary with more favorable salinity and mois-
ture conditions, although our preliminary observa-
tions and the studies of salinity in our region men-
tioned above suggested we might find a reverse in
the elevational pattern found for LIDU in southern
California.
In this study, we investigated LIRA and LIDU’s dis-
tribution, and how the invasion potential of LIRA,
which we determined to be the more abundant spe-
cies, varies with abiotic factors in the estuary. Our
objectives were to:
1. Document LIRA and LIDU populations in estu-
ary marshes, because mapping is an important
tool for invasive species management (Lass and
Callihan 1993) and provides a baseline for detect-
ing population increases (Webster and Cardina
1997);
2. Measure LIRA’s elevational range relative to tides
at three marshes to better understand the plant’s
distribution within and among marshes;
3. Characterize edaphic characteristics (salinity,
moisture, texture, and bulk density) across LIRA’s
elevational range to identify conditions that may
influence LIRA’s spread; and
4. Across LIRA’s elevational range, measure indica-
tors of its invasion success—rosette size, inflo-
rescence height, seed production, percent cover,
recruitment, spread over 1 year, and spread ver-
sus native plants during fall–winter (a time when
Hubbard and Page [1997] found LIDU spreads at
JUNE 2014
5
the expense of native plants)—and relate these
findings to soil properties.
MATERIALS AND METHODS
Distribution and Abundance of LIRA and LIDU
We located non-native sea lavender populations in
the estuary using field searches and outreach (e.g.,
querying colleagues). Beginning in 2007 through
2010, we searched marshes and shoreline within a
few kilometers of known populations, repeating this
process when occurrences of LIRA and LIDU were
found or reported through 2010. Mapping weeds
via landscape searches leverages knowledge of local
experts but may miss locations considered unlikely
to be invaded (Barnett et al. 2007). To augment our
approach, in 2010, a spatially explicit species dis-
tribution model (SDM) was developed and used to
identify LIRA habitat in south San Francisco Bay
(South Bay). We used the model to guide 18 days of
boat and ground searches, leading to
the identification of additional LIRA
populations (Archbald 2010b). We did
not generate a SDM for LIDU because
initial searches and outreach found it
to be considerably less widespread.
Once identified, we mapped popu-
lations at the patch scale using a
handheld Trimble GeoXH Global
Positioning System (GPS) (sub-meter
accuracy). We mapped only one LIDU
population (at Strawberry Marsh in
Richardson Bay), otherwise relying on
colleagues for LIDU population loca-
tions. We defined patches as one or
more sea lavender plants separated
by at least one meter and visually
estimated LIRA percent cover in each
patch to the nearest 5%. During map-
ping, we noticed that larger patches
appeared to have higher LIRA percent
cover than smaller patches, so we
evaluated the relationship between
individual patch sizes and LIRA percent cover using
regression analysis. We noted marsh substrate and
plant communities where invasive sea lavenders
were present and investigated the history of invaded
marshes using the San Francisco Estuary Institute’s
Wetland Tracker website (SFEI 2010).
Study Sites
We monitored and measured soil properties and
indicators of LIRA success across LIRA’s elevational
range between March 2008 and June 2009 at Sanchez
Marsh (hereafter Sanchez), Coyote Point Marina (here-
after Coyote), and Seal Slough (hereafter Seal)—three
marshes in the southwest estuary (Figure 2). Sanchez
(37.5878° N, -122.3537° W) is a saline to seasonally
brackish remnant tidal marsh. In 1987, a compensato-
ry mitigation project restored tides to 1.3 ha of former
wetlands at Sanchez by grading filled marsh back to
tidal elevations along the southern edge of the marsh
Figure 2 Mensurative studies were carried out at three marshes on the west side
of south San Francisco Bay, California: Sanchez Creek Marsh in Burlingame, Coyote
Point Marina in San Mateo, and Seal Slough in Foster City
SAN FRANCISCO ESTUARY & WATERSHED SCIENCE
6
(SFEI 2010). Other alterations at Sanchez include
earthwork associated with installation of electrical
towers in the marsh and storm drains, which empty
into the high marsh. Coyote (37.5901° N, -122.3148°
W) is a 2-km-long remnant tidal marsh that extends
along the bayward edge of the breakwall levee on the
east side of Coyote Point Marina. The marsh substrate
along the levee slope has an abundance of chert and
concrete cobbles. Seal, located at the mouth of Seal
Slough (37.5736° N, -122.2851° W), has been altered
via a major re-routing of the slough’s historic path to
the estuary (SFEI 2010). Our study site was located in
the southern end of the marsh, a portion of the marsh
that is exposed to high wind wave energy evidenced
during the study period by migrating oyster shell
berms and by active marsh erosion with the accumu-
lation of large areas of wrack.
Elevational Range of LIRA Relative to Tides
We measured the estimated ten highest and low-
est occurrences of LIRA using a Leica GX1230 Real
Time Kinetic (RTK) GPS (estimated post-correction
vertical accuracy 10-mm root mean square error)
(Leica Geosystems 2013) at Sanchez, Coyote, and
Seal in June of 2010. We displayed LIRA’s verti-
cal range (in NAVD88) as boxplots relative to tidal
datums [mean high water (MHW) and mean higher
high water (MHHW)] and 100-year flood elevations
(USACE 1984) using the R statistical package. Tidal
datums have been used to describe the distribution of
marsh vegetation in the estuary (Hinde 1954; Atwater
et al. 1979; Takekawa et al. 2012), and the 100-
year flood elevation shows the approximate upper
reach of tidal inundation. We obtained tidal datum
values referenced to mean lower low water (MLLW)
from 16 surrounding National Ocean Service (NOS)
water level stations from the http://www.noaa.gov
website (NOAA CO–OPS 2010), and point locations
of 100-year flood elevation data (in NAVD88) from
the Pacific Institute website (PI 2011). We converted
MLLW referenced tidal datums to NAVD88 using the
“Benchmarks” page at http://www.tidesandcurrents.
noaa.gov, when conversions were available (NOAA
CO–OPS 2010); otherwise, we used a conversion table
developed by NOS for the South Bay (Foxgrover et
al. 2005). We interpolated the tidal datum and flood
elevation point data, then extracted values from the
output rasters at the study sites using ArcGIS 9.1
(Archbald 2010c).
Study Design
At Sanchez, Coyote, and Seal, in March 2008, we
established 30 randomly located 1-m
2
sampling plots
(90 plots total) equally divided between vegetated
Figure 3 Survey plots (n = 5) were established at Sanchez Creek Marsh, Coyote Point Marina, and Seal Slough study sites to measure
indicators of invasion success and soil properties in and out of LIRA patches across LIRAs elevational range
Elevation
HIGH
MED
HIGH
MED
LOW LOW
Native marsh vegetation
LIRA patch
Survey plot
Elevation
HIGH
MED
HIGH
MED
LOW LOW
Native marsh vegetation
LIRA patch
Survey plot
Elevation
HIGH
MED
HIGH
MED
LOW
HIGH
MED
LOW LOW
Native marsh vegetation
LIRA patch
Survey plot
JUNE 2014
7
marsh in and out of LIRA patches, and stratified
across high, medium, and low elevations relative to
the vertical range of the invader (n = 5) (Figure 3).
We set the elevation of plot positions using a Topcon
laser level to ensure that elevations of plots in and
out of LIRA patches were comparable within marshes
(see Appendix A, Figure A-1) and then surveyed plot
positions relative to the NAVD88 geodetic datum
with a Leica GX1230 RTK GPS.
Soil Properties
We collected one soil core (10-cm depth, 4-cm
diameter) per plot in LIRA patches (45 plots total) to
measure salinity and moisture during low tides in
March 2008. We collected one soil core in and out of
LIRA patches (90 plots total) in September 2008 to
measure salinity, moisture, texture, and bulk density.
Nearby, rainfall was 19.8, 5.2 and 0.1 cm in January,
February, and March of 2008, respectively, then
negligible through September 2008 (San Francisco
International Airport data; ~16 km from all study
sites). In the lab, we weighed cores wet and dry to
determine percent moisture and bulk density (g cm
-3
),
measured relative soil salinity using saturated soil
pastes and a refractometer (Richards 1954) and
measured soil texture using the hydrometer method
(Bouyoucos 1962).
Indicators of Invasion Success
During peak LIRA flowering (July 2008) we mea-
sured the height and diameter of the ten largest LIRA
rosettes per plot and the height and number of inflo-
rescences per rosette. At Coyote, in August 2008, we
collected one representative inflorescence from all
LIRA plots and counted seeds per inflorescence to
derive seeds per plant at each elevation. We measured
LIRA percent cover in all invaded plots in March
2008 and March 2009 by placing a 1-m
2
quadrat
subdivided into 100 cells over each plot and record-
ing presence or absence of LIRA in every other cell.
To quantify recruitment, we measured in March 2009
percent cover of LIRA in plots that had no LIRA in
March 2008. Finally, we measured the percent cover
of plant species in all plots (45 with and 45 without
LIRA) in August 2008 and March 2009 to test spread
of LIRA versus native plants. This period spans the
late-winter period, a time when the invasive sea lav-
ender, LIDU, has been found to grow while native
marsh plants senesce (Hubbard and Page 1997).
Statistical Analysis
At Sanchez and Coyote, the LIRA distribution divided
into low, medium, and high study plots was similarly
situated relative to tides, but LIRA at Seal was dis-
tributed over a narrower vertical range and situated
0.1 to 0.2 m higher (Figure A-1). Therefore, when
testing the effect of LIRA and/or elevation on soil
properties and invasion success measurements, we
assessed Seal separately. We used IBM SPSS Statistics
20 to perform statistical analyses.
Patterns by Marsh, Elevation, and Season in LIRA
Patches. We tested how soil salinity and moisture in
LIRA plots varied with two time points in spring and
summer (March 2008 versus September 2009) and
elevation using 2-way repeated measures MANOVA
for Sanchez and Coyote and 1-way repeated measures
MANOVA for Seal. Data were transformed to meet the
assumptions of the statistical tests.
In and Out of LIRA Patches. We evaluated how soil
salinity, moisture, texture, and bulk density differed
between plots established in and out of LIRA patches.
Test assumptions were met when we used separate
3-way ANOVAs at Sanchez and Coyote and 2-way
ANOVAs at Seal. Percent sand was used as the indi-
cator of texture in statistical analysis. We used mean
texture measurements (percent sand, silt, and clay) to
describe soil types in and out of LIRA patches at each
marsh (USDA [cited 2013]).
Morphometric Response to Elevation. We tested the
response of LIRA rosette height, rosette width, num-
ber of inflorescences, and percent cover of LIRA
(March 2008) to elevation and marsh (at Sanchez
and Coyote) using 2-way MANOVA (inflorescence
height was excluded to limit dependent variables to
SAN FRANCISCO ESTUARY & WATERSHED SCIENCE
8
RESULTS
Distribution and Abundance of LIRA and LIDU
From 2007 to the end of 2010, 20 populations of
LIRA and 5 populations of LIDU were found, total-
ing 15,655 m
2
(~1.6 hectares) of invaded upper salt
marsh habitat (Table 1, Figure 4). LIRA was found in
far greater abundance (30:1 by area) with populations
ranging in size from a single plant to 4,357 m
2
, while
LIDU populations ranged in size from a few plants
to about 300 m
2
. Populations of LIRA were primarily
found in the South Bay region of the estuary with
small populations in the Central Bay. In contrast,
populations of LIDU were mainly in Richardson Bay,
though one was identified as far north as San Pablo
Bay (Table 1, Figure 4).
The largest populations of LIRA were found in
habitats with a history of disturbance to the marsh
substrate and vegetation. For example, at Sanchez
(the largest population), LIRA primarily occupied a
portion of the marsh that had been graded for resto-
ration (SFEI 2010; see Appendix A, Figure A-2), as
well as in other clearly disturbed locations includ-
ing at the base of power towers, along constructed
earthen berms, in bare patches, and near the base
of a drainage outflow pipe strewn with debris. The
large LIRA populations at San Francisco International
Airport (3,858 m
2
), Coyote (2,301 m
2
), and Oyster
Point Marina (1,596 m
2
) were all in upper salt marsh
areas at the filled margins of the estuary. Marsh sub-
strates at these sites appeared to be a mix of coarse
and fine-grained sediments and larger debris (e.g.,
concrete rubble, cobbles). LIRA was also found grow-
ing on cobble-dominated substrate at Ideal Marsh
(317 m
2
). At Greco Island and Bird Island, individual
colonizing LIRA plants were found on (apparently)
native sediments near the high tide / wrack line in
areas of low native plant cover. LIRA occurrences
were also mapped in naturally occurring sandy and
coarse grain substrates, including oyster shell hash
berms at Beach Park (20 m
2
), and above the high tide
line at a small beach north of Coyote Point Marina
(North Coyote Point) (449 m
2
) (Table 1, Figure 4).
n
1 and is displayed graphically only). Dependent
variables were transformed to meet parametric test
assumptions. We tested the same dependent vari-
ables (transformed) using a 1-way MANOVA at Seal.
Because seeds were counted at Coyote only, we tested
the effect of elevation group on number of seeds per
inflorescence using 1-way ANOVA.
Spread. We measured change in percent cover of LIRA
in those plots that were not buried or eroded between
March 2008 and March 2009 and that did not have
100% cover at the start of the survey. Thirty-one plots
met these criteria: 7 from Sanchez, 15 from Coyote,
and 9 from Seal. MANOVA was precluded due to vio-
lation of the assumption of homogeneity of variance-
covariance matrices, so one-way ANOVAs were used
to test the effect of elevation on spread rate within
each marsh individually.
Recruitment. We included in our analysis the 36 plots
that had zero LIRA in March 2008 and that were not
lost to erosion or burial through March 2009. Change
in percent cover of LIRA could not be transformed
adequately, so recruitment was converted to count
data with a Poisson distribution by assuming each
observation of LIRA from percent cover data (2%
cover) equals one seedling, then a Poisson log-linear
model was used to test for an effect of elevation and
marsh on establishment (Quinn and Keough 2003).
Competition. We tested how percent cover of three
native plants that commonly co-occurr with LIRA,
S. pacifica, Jaumea carnosa (jaumea), and D. spicata
changed with marsh, elevation, and presence versus
absence of LIRA over a 6-month period (August 2008
to March 2009) using 3-way MANOVA. We excluded
Seal from this analysis because nearly half the plots
were lost to burial, erosion, and wrack during this
time period. Dependent variables were multimodal;
hence, we used a rank transformation, the suggested
approach when no non-parametric alternative exists
for the test (Conover 1998).
JUNE 2014
9
The vast majority (538 out of 558) of LIRA patches
were under 200 m
2
, and these patches had 27%
cover on average. In contrast, patches larger than
200 m
2
had 70% cover on average. Both average and
maximum LIRA patch cover were generally higher
in larger populations (Table 1), and LIRA cover
Table 1 Limonium ramosissimum subsp. provinciale and Limonium duriusculum mapping statistics
Location (north to south) Latitude Longitude
Year
mapped
Average
patch cover
(%)
± 1 S.E.
Maximum
patch cover
(%)
No.
of patches Area (m
2
)
Limonium ramosissimum subsp. provinciale
Corte Madera 37.9396 -122.5060 2010 5 ± 0 5 1 1
Albany Bulb 37.8889 -122.3100 2009 28 ± 10 45 3 32
Sausalito 37.8750 -122.5080 2010 5 ± 0 5 1 1
Pier 94 37.7460 -122.3760 2008 5 ± 0 5 2 2
Yosemite Slough 37.7220 -122.3830 2008 7 ± 2 15 5 5
Candlestick Point State Park 37.7091 -122.3790 2008 5 ± 0 5 2 2
Oyster Point Marina 37.6626 -122.3750 2008 32 ± 5 8 28 1596
San Francisco Intl. Airport 37.6104 -122.3740 2008 37 ± 3 90 58 3858
Whale’s Tail 37.6008 -122.1460 2010 13 ± 3 50 17 38
Coyote Point Marina 37.5893 -122.3150 2010 25 ± 2 80 83 2301
Sanchez Creek Marsh 37.5888 -122.3560 2010 43 ± 2 95 154 4357
North Coyote Point 37.5877 -122.3340 2008 15 ± 0 15 1 449
Seal Slough 37.5745 -122.2850 2010 18 ± 2 80 111 519
Beach Park 37.5629 -122.2490 2010 29 ± 6 75 12 20
Bird Island 37.5517 -122.2430 2010 5 ± 0 5 1 1
Ideal Marsh 37.5358 -122.1140 2010 16 ± 3 80 42 317
Greco Island 37.5214 -122.2020 2010 5 ± 0 5 1 1
Plummer Creek Marsh 37.5131 -122.0533 2010 500
a
Outside Pond R1 37.5041 -122.1480 2010 11 ± 4 40 9 12
Coyote Creek Lagoon 37.4770 -121.9530 2010 32 ± 5 80 28 1132
Totals 558 15,144
Limonium duriusculum
Guadalcanal 38.1181 -122.2889 2010 -- -- -- 5
Greenbrae Boardwalk 37.9427 -122.5136 2010 -- -- -- 8
Strawberry Marsh 37.8890 -122.5126 2008 -- -- -- 178
Seminary Drive #1 37.8880 -122.5104 2010 -- -- -- 300
Seminary Drive #2 37.8858 -122.5106 2010 -- -- -- 20
Total 511
a. Extent estimated from aerial imagery following site visit by W. Thornton.
increased logarithmically with patch size (R
2
= 0.32,
P < 0.0001, Figure A-3).
Elevational Range of LIRA Relative to Tides
LIRA at Sanchez and Coyote had nearly identical ele-
vational ranges, while at Seal, LIRA was absent from
SAN FRANCISCO ESTUARY & WATERSHED SCIENCE
10
lower elevations. LIRA’s elevation range was 1.77 to
2.51 m NAVD88 at Sanchez and Coyote and 2.05 to
2.43 m NAVD88 at Seal. Relative to tidal datums,
LIRA ranged from 0.09 m below MHW to 0.42 m
above MHHW at Sanchez and Coyote. At Seal, plants
extended from 0.02 m below MHHW to 0.36 m above
MHHW (Figure 5).
Marsh Plant Community Invaded
At Sanchez and Coyote, native species J. carnosa,
S. pacifica, and D. spicata were common across
LIRA’s vertical range (Table 2). A native halophyte
indicative of the high marsh, Frankenia salina (alkali
heath) was most abundant (18.8% cover) in low
elevations of LIRA's range. The native sea lavender,
L. californicum, occurred across LIRA’s range. At
Coyote, G. stricta commonly co-occurred with LIRA
at the invader's medium and high elevations (8.8%
and 15.6% cover, respectively). At LIRA's highest
elevations, species less tolerant of salinity and inun-
dation were present, including Plantago coronopus
(buckhorn plantain), Avena fatua (common wild oat),
Foeniculum vulgare (fennel), and Lolium multiflorum
(Italian rye grass). At Seal, at LIRA's medium and
high elevations, an alkali grass (Puccinellia sp.) was
commonly found.
Soil Properties
Patterns by Marsh, Elevation, and Season in LIRA
Patches. In March 2008, soil salinity within each
marsh was highest at the low end of LIRA’s eleva-
m NAVD88m NAVD88
Figure 5 Vertical range (m NAVD88) of LIRA at study sites relative
to tidal datums measured with RTK GPS in 2008. Box plots show the
median, first, and third quartile of elevation measurements; whis-
kers show the range.
Figure 4 Relative size and location of populations of L. ramo-
sissimum subsp. provinciale and L. duriusculum mapped in
the San Francisco Estuary from 2008 through 2010. Strawberry
Marsh includes Seminary Drive #1 and Seminary Drive #2 (see
Table 1).
JUNE 2014
11
Table 2 Average percent cover of species, wrack, and bare ground in survey plots in and out of Limonium ramosissimum subsp.
provinciale (LIRA) patches in September 2008
Species
Average Percent Cover
Sanchez Creek Marsh Coyote Point Marina Seal Slough
Elevation
IN LIRA PATCHES Low Med High Low Med High Low Med High
Atriplex prostrata
a
0.8%
Avena fatua
a,b
5.2% 4.0%
Cuscuta pacifica
c
0.4% 4.8%
Distichlis spicata
c
57.6% 56.0% 46.0% 14.8% 39.2% 2.8% 0.8% 0.0% 18.4%
Foeniculum vulgare
a,b
2.2%
Frankenia salina
c
18.8% 1.2% 1.2% 0.5%
Grindelia stricta
c
0.4% 0.8% 8.8% 15.6%
Jaumea carnosa
c
92.0% 74.8% 56.0% 89.6% 65.6% 12.4% 38.8% 0.4%
Limonium californicum
c
8.4% 5.2% 0.4% 4.8% 3.2% 7.2% 10.0% 0.8%
Limonium ramosissimum
subsp. provinciale
a
58.8% 99.2% 97.2% 66.8% 90.0% 90.4% 54.0% 26.0% 43.2%
Lolium multiflorum
a,b
5.6%
Plantago coronopus
a,b
1.2% 3.6% 0.4%
Puccinellia sp.
d
5.6% 14.4% 10.8% 8.8% 3.6% 22.8% 42.4% 39.5% 33.6%
Salicornia pacifica
c
68.8% 16.4% 17.2% 67.2% 47.2% 45.6% 49.2% 33.0% 26.0%
Salsola soda
a
0.4%
Trifolium sp.
b,d
Bare Ground 2.8% 20.0% 23.6%
Wrack 73.8% 39.0%
OUT OF LIRA PATCHES
Atriplex prostrata
a
0.8%
Cuscuta pacifica
c
2.0% 1.2% 27.2% 0.8%
Distichlis spicata
c
65.6% 79.6% 39.2% 41.6% 36.0% 73.6% 1.0% 2.0% 23.5%
Frankenia salina
c
0.8%
Grindelia stricta
c
13.2% 3.6% 9.6% 14.0% 26.0% 7.5%
Jaumea carnosa
c
99.6% 98.0% 43.2% 71.6% 43.2% 3.2% 3.5% 1.0%
Limonium californicum
c
2.0% 6.0% 2.5%
Limonium ramosissimum
subsp. provinciale
a
4.4% 0.4% 1.6% 3.2% 1.6% 0.5% 0.5%
Plantago coronopus
a
4.0%
Puccinellia sp.
d
18.8% 20.0% 88.0% 25.0%
Salicornia pacifica
c
67.2% 65.2% 75.6% 93.6% 90.4% 81.6% 97.5% 75.0% 58.5%
Salsola sola
a
9.6% 0.8%
Spartina sp.
d
7.2%
Trifolium sp.
b,d
5.2%
Triglochin maritima
c
8.4%
Bare Ground 2.0% 2.0% 21.5%
Wrack 23.8% 68.8% 33.8%
a. Non-native plant.
b. Typically associated with upland habitats.
c. Native halophyte.
d. Native / non-native status not identified.
SAN FRANCISCO ESTUARY & WATERSHED SCIENCE
12
tional range and decreased with elevation (Figure 6;
Appendix B, Tables B-1, B-2). Average salinity at
low elevations at Sanchez and Coyote was ~28 ppt,
57% lower at mid-elevations (~12 ppt) and another
50% lower (~6 ppt) at high elevations of LIRA dis-
tribution. Soil salinity at Seal also decreased from
low to high elevations (Figure 6, Tables B-1, B-2).
Soil percent moisture decreased from about 33% to
18% from low to high elevations at both Sanchez
and Coyote. Soil moisture at Seal also decreased with
elevation but was lower overall than at the other
marshes (Figure 6, Tables B-1, B-2).
In September 2008, soil salinities were higher across
marshes compared to March measures (significant
effect of time on salinity, Tables B-1, B-2), as high
as 55 ppt at low elevations and 26 ppt at high eleva-
tions (Figure 6). The inverse relationship of salin-
ity and elevation still held at Sanchez and Coyote;
however, at Seal, salinities were similar with eleva-
tion (~38 ppt) unlike in March (time × elevation
effect on salinity, Table B-1). Patterns in moisture in
September 2008 were comparable to those in March
(Figure 6, Tables B-1, B-2).
In and Out of LIRA Patches. At Sanchez and Coyote in
September 2008, soil bulk density was significantly
higher (P = 0.025) and moisture was significantly
lower (P = 0.035) in versus out of LIRA patches.
Salinity and percent sand did not differ with LIRA
presence. At Seal, none of the four measured soil
properties differed significantly in and out of LIRA
patches (Figure 7). Assessing texture averaged across
elevations, soils were sandy loam at Sanchez, Coyote,
and Seal, regardless of LIRA presence.
Both in and out of LIRA patches in September 2008,
salinity and moisture decreased significantly with
elevation (P < 0.0001 for both, no interaction with
LIRA presence) but neither bulk density nor percent
sand showed an elevation effect (Figure 7). Between
Sanchez and Coyote, bulk density and percent
sand differed (P = 0.020 and P = 0.004, respectively),
with bulk density higher and percent sand lower at
Sanchez. At Seal, soil moisture declined (P < 0.0001)
and percent sand increased (P = 0.001) with elevation,
Figure 6 Seasonal variation (March and September 2008)
in soil salinity (ppt) and moisture (%) within LIRA patches at
Sanchez, Coyote, and Seal marshes across LIRAs elevational
range. Error bars represent ±1 S.E.
JUNE 2014
13
Figure 7 Soil properties relative to elevation
(See Figure 4), marsh, and in versus out of LIRA
patches from cores collected in September 2008.
Error bars represent ±1 S.E.
Figure 8 Comparison of LIRA size (July 2008),
inflorescence production (July 2008), seed pro-
duction (August 2008), and percent cover (March
2008) with elevation at the three study marshes.
Seeds per inflorescence measured at Coyote only.
Error bars represent ±1 S.E.
SAN FRANCISCO ESTUARY & WATERSHED SCIENCE
14
but soil salinity and bulk density were similar across
elevations (Figure 7).
Indicators of Invasion Success
Morphometric Response to Elevation. Rosette height,
diameter, number of inflorescences per plant,
and percent cover of LIRA increased significantly
with elevation at Sanchez and Coyote (Figure 8,
P = 0.0002; no effect of marsh or interaction). By con-
trast, there was no multivariate effect of elevation on
morphometric response variables at Seal (P = 0.483).
Rosette height increased from low to high elevation
at Sanchez and Coyote, from ~ 3.8 to 8.0 cm; the
increase was more moderate at Seal, where rosette
heights ranged from 5.9 to 7.7 cm. Rosette diameter
also increased with elevation from ~6 to 12 cm at
Sanchez and Coyote with a more muted range of 11.1
to 11.6 cm at Seal. Number of inflorescences, too,
increased with elevation at Sanchez and Coyote, from
8.7 to ~18 inflorescences per plant; however, there
was no difference at Seal from low to high eleva-
tion (~17 inflorescences throughout). Cover of LIRA
at Sanchez and Coyote was ~56% at low and 95% at
high elevations: at Seal, LIRA ranged in cover from
39% to 53% with increasing elevation. Inflorescence
height was not assessed statistically but showed simi-
lar patterns (Figure 8). Seeds per inflorescence, evalu-
ated only at Coyote, increased from ~375 to nearly
1000 from low to high elevation (Figure 8, P = 0.002).
Spread. Between March 2008 and March 2009,
deposition of Spartina (cordgrass) wrack and wind-
Figure 9 Change in percent cover of LIRA within plots in
LIRA patches, by elevation, at the three study marshes over
1 year (March 2008 to 2009). Figure includes plots lost to burial
and erosion, and plots that began with 100% cover. Error bars
represent ±1 S.E.
Figure 10 Change in percent cover in native plants (S. paci-
fica, J. carnosa, and D. spicata) in plots in and out of LIRA
patches across elevations at Sanchez and Coyote from August
2008 to March 2009. Seal data were excluded because nearly
half the plots were lost to burial, erosion, and wrack. Error
bars represent ±1 S.E.
S. pacifica
D. spicata
J. carnosa
S. pacifica
D. spicata
J. carnosa
JUNE 2014
15
wave erosion caused near total loss of vegetation in
some plots at Seal: some plots at Sanchez initially
had 100% cover, precluding measurement of further
increase. Change in cover of LIRA was highly vari-
able if all those plots were included in calculations
(Figure 9). Excluding those plots, percent cover of
LIRA tended to increase (on average by 11.0%) across
marsh and elevation treatments. Increases in percent
cover ranged from 7.7% at Sanchez, to 9.1% at Seal,
to 13.6% at Coyote. No difference in LIRA spread
as a function of elevation was found at any marsh
based on 1-way ANOVAs (all P
> 0.38).
Recruitment. One or more LIRA seedlings recruited
between August 2008 and March 2009 in 27.8%
of the plots assessed at Coyote, Sanchez, and Seal.
Plots were colonized more frequently by LIRA at
high (36.4%) than medium (33.3%) or low eleva-
tions (15.4%). Elevation significantly affected the
number of plots colonized by LIRA (χ
2
= 6.427, df = 2,
P = 0.040), but there was no difference in seed-
ling recruitment among marshes (χ
2
= 2.350, df = 2,
P = 0.303).
Competition. From August 2008 to March 2009, all
three native halophytes lost significantly more cover
in LIRA patches than occurred in surrounding veg-
etation (Figure 10, MANOVA effect of LIRA pres-
ence, P
= 0.001) and this effect was consistent among
marshes and elevations (no interactions). Negative
effects of LIRA presence were most pronounced in
the case of D. spicata at Sanchez (Figure 10), with
a mean 21% decline in cover. Overall, there was a
greater decline in native plant cover at Sanchez than
at Coyote (Table B-3).
DISCUSSION
Although the presence of introduced Limonium spe-
cies in the estuary was only first recognized in 2007,
we documented widespread occurrence in our sur-
vey from 2008 to 2010, with 25 populations cover-
ing ~1.6 hectares of high marsh and transition zone
habitat. LIRA, by far the most common species, had
populations concentrated in and around Sanchez,
near the San Francisco International Airport. LIRA’s
abundance in this region and prodigious seed pro-
duction suggest that propagule pressure, a strong
driver of species invasions (Simberloff 2009), is likely
highest along the west side of the south estuary. Both
LIRA and LIDU populations were generally located ~2
to 8 km from other invaded marshes, suggesting inva-
sion potential may be highest in this range. However,
LIRA populations were also identified ~18 km from
known seed sources and a single LIDU population
was found ~30 km from other populations. Therefore,
LIRA and LIDU are also either capable of dispers-
ing across long distances, or multiple introductions
of each species have occurred. As we know of two
cases of accidental planting or seeding at restora-
tion sites (see Introduction), human-mediated disper-
sal may have played a role in the distributions we
documented.
Habitats Susceptible to Invasion
LIRA and LIDU have primarily established in human-
and naturally-disturbed upper salt marsh habitats.
Disturbance often increases resources such as space,
light, and nutrients (Davis et al. 2000), creating
opportunities for colonization (Horvitz et al. 1998;
Shea and Chesson 2002; Renz et al. 2012). Many
non-native plants gain a foothold in disturbed sites
and then invade adjacent undisturbed habitat (Hobbs
and Huenneke 1992), a scenario that seems possible
for LIRA but that has not been observed to date. Our
finding of lower soil moisture and higher bulk den-
sity in LIRA-invaded areas suggests that LIRA may
be particularly well suited to, or contribute to, these
conditions.
LIRA’s elevational range across Sanchez, Coyote,
and Seal (1.77 to 2.51 m NAVD88, or 0.75 to 1.49 m
above MSL) corresponds with the high marsh (0.7 to
1.0 m MSL) and upland transition zone (>
1.0 m MSL)
in estuary tidal marshes (Takekawa et al. 2012).
At the low end of its range, LIRA occurred with
S. pacifica, J. carnosa, D. spicata, F. salina, and L.
californicum, species indicative of the high marsh
(Atwater and Hedel 1976; Josselyn 1983; Takekawa
SAN FRANCISCO ESTUARY & WATERSHED SCIENCE
16
et al. 2012). At the upper end of its range, LIRA
was found with both native high marsh halophytes
and with upland species (e.g., F. vulgare, A. fatua,
and Trifolium spp.) typical of the transition zone
(Wasson and Woolfolk 2011). Importantly, these
findings indicate LIRA can tolerate inundation condi-
tions coincident with mature tidal salt marsh plains,
which stabilize near MHHW, and occur in younger
pickleweed-dominated marshes, which are typically
a few decimeters lower (near MHW; Atwater and
Hedel 1976). Further, invasion of the transition zone
may lead to a loss of species that contribute to high
species richness there, including rare species such as
Chloropyron maritimum subsp. palustre and Suaeda
californica, which we have observed growing among
LIDU and LIRA patches, respectively.
LIRA was found across a soil salinity gradient that
decreased from the high marsh into the transition
zone, a salinity pattern consistent with findings in
the estuary (Mahall and Park 1976; St. Omer 2004),
at Pt. Reyes National Seashore (Traut 2005), in
Elkhorn Slough (Harvey et al. 1978; Byrd and Kelley
2006), and in cooler climates (Oregon: Seliskar 1985),
but contrasting with patterns in southern California
marshes where soil is hypersaline during summer
months through the transition zone up to maximum
high water (Callaway et al. 1990). Soil moisture,
too, decreased with elevation across LIRA’s vertical
range. Declining moisture across this vertical range
is well established, but our soil moisture values were
lower than similar studies. Traut (2005) found mois-
ture decreased from 40% to 15% from mid-marsh
into upland soils in June and July. St. Omer (2004)
found little variation in moisture seasonally in the
high marsh, but moisture ranged from 47% to 62%.
Texture was not reported for either study, but it is
possible that moisture values were lower at our study
sites because of: (1) high sand content in the soils in
our study, which leads to lower water-holding capac-
ity (Brady and Weil 1999), and (2) lack of adjacent
upland with a concurrent water table. Together, these
findings support a conceptual model of LIRA as a
species that can establish in both dry, sandy soils as
well as moist, seasonally hypersaline soils.
Indicators of Invasion Success
Across our study sites, LIRA size and reproductive
output noticeably increased above MHHW, particu-
larly in the transition zone where soil moisture and
salinity were lowest. Below MHHW, higher salinity
and inundation likely limit the size and reproduc-
tive output of LIRA. This fits with prior studies of
Limonium species (e.g., Boorman 1971) and with
upper salt marsh species in general (e.g., Cooper
1982; Seliskar 1985; Schile et al. 2011; Ryan and
Boyer 2012). Since LIRA grows largest in low stress
conditions, we suspect it may compete most aggres-
sively within the transition zone.
Seed output for LIRA at Coyote was orders of mag-
nitude higher than LIDU seed output reported by
Hubbard and Page (1997), which ranged from 360
to 11,400 seeds per square meter at Carpinteria
Salt Marsh in Santa Barbara. At Coyote, we found
LIRA seed output ranged from about 3,000 to about
17,400 seeds per plant, depending on elevation.
Assuming seed production at Sanchez and Seal is on
par, we estimate LIRA seed output typically ranges
from about 36,000 to 130,000 seeds per square meter
at low versus high elevations, respectively. This dif-
ference alone may explain why LIRA is more wide-
spread than LIDU in the estuary. In the highly invad-
ed marshes near Sanchez, we observed carpet-like
growth of hundreds of LIRA seedlings in and around
LIRA patches. Furthermore, LIRA cover was consis-
tently high in large patches (mean of 70% cover in
patches over 200 m
2
). These observations suggest
that, once established in suitable habitat, infilling of
space between LIRA plants is likely aided by intense,
local propagule pressure within marshes.
Over one year, LIRA’s rate of spread (11%) was
consistent with average invasive plant spread rates
across western wildlands (Asher and Dewey 2005).
LIRA recruitment was greatest at high elevations,
suggesting seeds are more frequently distributed
by tidal action to higher elevations, germinate and
establish more readily at higher elevations, or both.
No difference in recruitment was found between
marsh sites, which was unexpected since Sanchez
JUNE 2014
17
and Coyote have considerably larger populations (and
hence seed production) than Seal. These findings sug-
gest that seed from adjacent populations may con-
tribute significantly to recruitment at Seal.
We found native plant cover rebounded less after
winter senescence in LIRA patches. In Carpinteria Salt
Marsh, Hubbard and Page (1997) found LIDU was
associated with decreased native plant cover over the
course of 1 year, and attributed this to LIDU’s abil-
ity to grow when most native plants senesce. In our
study at Sanchez and Coyote, S. pacifica, J. carnosa,
and D. spicata cover was lower over 6 months with
LIRA present. We hypothesize that LIRA may draw
down nutrients and/or physically expand during
winter, thereby reducing resources available to other
plants emerging from winter senescence. A longer
study period that includes summer months is needed
to verify LIRA’s effect on native plant cover.
Transition zone habitats provide important high tide
refuge for endangered vertebrates, and this func-
tion depends, in part, on the physical structure of
the plants in the transition zone. Salt marsh harvest
mice, for example, require an overhead canopy for
protection from predators (Fisler 1965; Shellhammer
1989). LIRA rosettes, however, form dense, low-
growing (~3 to 10 cm tall) patches that likely provide
poor refuge from predators. Dense LIRA cover too, by
virtue of physically covering marsh substrate, may
impede seedling establishment of high marsh plants
such as G. stricta that provide essential nesting habi-
tat and high tide refuge for the endangered California
clapper rail (Evens 2010).
CONCLUSION
LIRA and LIDU appear well suited to invade dis-
turbed, sandy loam soils in upper salt marsh habitats
in the estuary. LIRA growth and reproductive output
are greatest in the transition zone where soil mois-
ture and salinity are lower, but the invader can also
establish, spread, and compete with native plants
in the high marsh above MHW. LIRA competes
with native high marsh and transition zone species
important as high tide refugia for endangered native
vertebrates. Combined with the many locations of
introduced Limonium we documented, this suggests
upper salt marsh habitats in the estuary are at risk
of invasion, with consequences for native special
status species conservation, and leads us to strongly
recom mend localized and regionally-coordinated
control efforts. Managers should regularly monitor
marshes located fewer than 8 km from known inva-
sion sites to identify and prevent spread between
marshes and should initiate removal efforts in the
transition zone in invaded marshes. Further, the
recent mis-identification and accidental introduction
of invasive sea lavenders to restoration sites in San
Francisco and in the South Bay suggest that outreach
and improved awareness are necessary to avoid fur-
ther human-mediated spread. Finally, genetic studies
are needed to help resolve the possibility of multiple
introductions as well as the potential for hybridiza-
tion (Palacios et al. 2000) among the established sea
lavender species in estuary marshes.
ACKNOWLEDGMENTS
Funding was provided by the San Francisco State
Department of Biology (including the Mentorship
in Quantitative Biology Program, NSF Grant No.
EF-046313), and College of Science and Engineering,
the ARCS Foundation, the South Bay Salt Ponds
Restoration Project, Northern California Botanists, the
Association for Environmental Professionals, and the
Romberg Tiburon Center for Environmental Studies
and the Graduate Mentorship in Quantitative Biology
Program. We thank T. Parker, M. Page, and P. Baye
for comments that improved earlier versions of the
manuscript, and staff of the California State Coastal
Conservancy’s Invasive Spartina Project for helping
to identify invasion locations. Site access was pro-
vided by the Don Edwards National Wildlife Refuge,
the City of Burlingame, and the County of San Mateo
Parks and Recreation.
SAN FRANCISCO ESTUARY & WATERSHED SCIENCE
18
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... provinciale [Pignatti] Pignatti; hereafter, LIRA), is one of several invasive sea lavenders from the western Mediterranean (Devillers-Terschuren and Devillers-Terschuren 2001) that have invaded salt marshes and tidal lagoons across California (Barbour et al. 2007;Consortium of California Herbaria 2012). Where studied in California salt marshes, LIRA has been found to spread rapidly within high marsh and transition zone habitats and to reduce cover of native halophytes (Archbald and Boyer 2014;M Page, personal communication). In the San Francisco Estuary (SFE), LIRA was only recently discovered, but has already invaded approximately 15,000 m 2 (3.7 ac) of saline tidal marshes in Central and South San Francisco Bay (Archbald and Boyer 2014). ...
... Where studied in California salt marshes, LIRA has been found to spread rapidly within high marsh and transition zone habitats and to reduce cover of native halophytes (Archbald and Boyer 2014;M Page, personal communication). In the San Francisco Estuary (SFE), LIRA was only recently discovered, but has already invaded approximately 15,000 m 2 (3.7 ac) of saline tidal marshes in Central and South San Francisco Bay (Archbald and Boyer 2014). However, factors influencing LIRA's potential for further spread within the SFE were largely unknown. ...
... In SFE, for example, the invasion of hybrid smooth cordgrass (Spartina alterniflora Loisel. X Spartina foliosa Trin) in marsh and mudflat habitats has likely been accelerated by an increase in available habitat via DOI: 10.1614/IPSM-D-13- (Archbald and Boyer 2014). ...
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This thoroughly revised, entirely rewritten edition of what is the essential reference on California's diverse and ever-changing vegetation now brings readers the most authoritative, state-of-the-art view of California's plant ecosystems available. Integrating decades of research, leading community ecologists and field botanists describe and classify California's vegetation types, identify environmental factors that determine the distribution of vegetation types, analyze the role of disturbance regimes in vegetation dynamics, chronicle change due to human activities, identify conservation issues, describe restoration strategies, and prioritize directions for new research. Several new chapters address statewide issues such as the historic appearance and impact of introduced and invasive plants, the soils of California, and more.
Chapter
Over the past 50 years, experience has shown that interagency groups provide an effective forum for addressing various invasive species issues and challenges on multiple land units. However, more importantly, they can also provide a coordinated framework for early detection, reporting, identification and vouchering, rapid assessment, and rapid response to new and emerging invasive plants in the United States. Interagency collaboration maximizes the use of available expertise, resources, and authority for promoting early detection and rapid response (EDRR) as the preferred management option for addressing new and emerging invasive plants. Currently, an interagency effort is underway to develop a National EDRR System for Invasive Plants in the United States. The proposed system will include structural and informational elements. Structural elements of the system include a network of interagency partner groups to facilitate early detection and rapid response to new invasive plants, including the Federal Interagency Committee for the Management of Noxious and Exotic Weeds (FICMNEW), State Invasive Species Councils, State Early Detection and Rapid Response Coordinating Committees, State Volunteer Detection and Reporting Networks, Invasive Plant Task Forces, and Cooperative Weed Management Areas. Informational elements and products being developed include Regional Invasive Plant Atlases, and EDRR Guidelines for EDRR Volunteer Network Training, Rapid Assessment and Rapid Response, and Criteria for Selection of EDRR Species. System science and technical support elements which are provided by cooperating state and federal scientists, include EDRR guidelines, training curriculum for EDRR volunteers and agency field personnel, plant identification and vouchering, rapid assessments, as well as predictive modeling and ecological range studies for invasive plant species.
Article
Experiments were conducted to test the accuracy of a global positioning system (GPS) in measuring the area of stimulated weed patches of varying size and to determine the accuracy in navigating back to particular points in a field. Circular areas of 5, 50, and 500 m2 were established and measured using point and polygon features of a GPS. The GPS estimations of the area of those patches had errors ranging from 7 to 45%, 6 to 15%, and 3 to 6%, respectively, when compared to actual measurements. As patch size increased, errors decreased. A curve describing the relationship between GPS error and patch size had an excellent fit (r2 = 0.92). The error remained the same in all measurements across all patch sizes, but composed a smaller percentage of large patches. The GPS had submeter accuracy in navigation to the correct quadrat 73% of the time, located the correct quadrat 27% of the time, and invariably navigated to within 1.58 m of the correct quadrat. The relationship between patch size and measurement error was applied to natural infestations of hemp dogbane.