Spartina alterniflora
(smooth cordgrass)

Pictures

Picture	Title	Caption	Copyright
Title Habit Caption Spartina alterniflora (smooth cordgrass); infestation of densely packed plants. USA. Copyright ©John M. Randall/The Nature Conservancy/Bugwood.org - CC BY-NC 3.0 US	Habit	Spartina alterniflora (smooth cordgrass); infestation of densely packed plants. USA.	©John M. Randall/The Nature Conservancy/Bugwood.org - CC BY-NC 3.0 US
Title Habit Caption Spartina alterniflora (smooth cordgrass); infestation of densely packed plants on a mudflat. USA. Copyright ©John M. Randall/The Nature Conservancy/Bugwood.org - CC BY-NC 3.0 US	Habit	Spartina alterniflora (smooth cordgrass); infestation of densely packed plants on a mudflat. USA.	©John M. Randall/The Nature Conservancy/Bugwood.org - CC BY-NC 3.0 US
Title Habit Caption Spartina alterniflora (smooth cordgrass); infestation of densely packed plants, showing flower spikes. USA. Copyright ©Fred Weinmann/Bugwood.org - CC BY-NC 3.0 US	Habit	Spartina alterniflora (smooth cordgrass); infestation of densely packed plants, showing flower spikes. USA.	©Fred Weinmann/Bugwood.org - CC BY-NC 3.0 US
Title Inflorescence Caption Spartina alterniflora (smooth cordgrass); inflorescence. USA. Copyright ©Joseph M. DiTomaso/University of California-Davis/Bugwood.org - CC BY-NC 3.0 US	Inflorescence	Spartina alterniflora (smooth cordgrass); inflorescence. USA.	©Joseph M. DiTomaso/University of California-Davis/Bugwood.org - CC BY-NC 3.0 US
Title Stem Caption Spartina alterniflora (smooth cordgrass); stem, showing collar and sheath. USA. Copyright ©Joseph M. DiTomaso/University of California-Davis/Bugwood.org - CC BY-NC 3.0 US	Stem	Spartina alterniflora (smooth cordgrass); stem, showing collar and sheath. USA.	©Joseph M. DiTomaso/University of California-Davis/Bugwood.org - CC BY-NC 3.0 US

Identity

Preferred Scientific Name

• Spartina alterniflora Loisel

Preferred Common Name

• smooth cordgrass

International Common Names

• English: Atlantic cordgrass; saltmarsh cordgrass; salt-water cordgrass

Summary of Invasiveness

S. alterniflora, along with other Spartina was initially seen by many coastal engineers as a species that could be used to create natural erosion control barriers. S. alterniflora is a rhizomatous perennial grass, grows 0.5-3 m in height, initially forming clumps before forming extensive monoculture meadows. Spartina spp. have a dense root/rhizome system that binds coastal mud and its sturdy stem decreases wave action allowing silt deposition, causing elevation of the mudbank, assisting in land reclamation. As a result, it was widely planted at coastal sites throughout the UK, Northern Europe, Australia, New Zealand, China and USA, where it has naturally colonized (via seed or vegetative fragments) large areas of tidal mudflats, becoming an invasive species. Natural habitats are altered to monoculture Spartina meadows, resulting in displacement of flora and fauna. Management of the S. alterniflora is expensive and time consuming, early prevention of invasion is recommended prior to its establishment.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Monocotyledonae
•                     Order: Cyperales
•                         Family: Poaceae
•                             Genus: Spartina
•                                 Species: Spartina alterniflora

Notes on Taxonomy and Nomenclature

Spartina is a relatively small genus consisting of approximately 14 species, geographically centered along the east coast of North and South America, with outliers on the west coast of North America, Europe, and Tristan da Cunha. Members of the genus occur primarily in wetlands, especially estuaries (Partridge, 1987).

Description

S. alterniflora is a rhizomatous perennial grass that grows initially in round, genetically similar, clumps ranging between 0.5-3m in height, eventually forming extensive monoculture meadows. The stems are hollow and hairless. The leaf blades are 3 to 25 mm wide. The leaves lack auricles and have ligules (1-2 mm) that consist of a fringe of hairs. The flowers (classified yellow, although visually seem white) are inconspicuous and are borne in greatly congested spikes, 2-5 cm long (Hitchcock et al., 1969). Along its introduced east coast range S. alterniflora flowers between late August and September. The plant is deciduous; its stems die back at the end of each growing season (Ebasco Environmental, 1992; Daehler and Strong, 1994).

Within its native range of the Atlantic and Gulf coastlines of USA, S. alterniflora exhibits two growth forms, at different salt marsh zones. A tall form occurs along creek banks and drainage channels. Landward of the tall form, an intermediate form occurs, which grades into a stunted form at the salt marsh interior (Smart, 1982).

A detailed description of S. alterniflora is provided by the Grass Manual on the Web (http://herbarium.usu.edu/).

Plants rhizomatous; rhizomes elongate, flaccid, white, scales inflated, not or only slightly imbricate. Culms to 250 cm tall, (0.3) 5-15(20) mm thick, erect, solitary or in small clumps, succulent, glabrous, having an unpleasant, sulphurous odor when fresh. Sheaths mostly glabrous, throat glabrous or minutely pilose, lower sheaths often wrinkled; ligules 1-2 mm; blades to 60 cm long, 3-25 mm wide, lower blades shorter than those above, usually flat basally, becoming involute distally, abaxial surfaces glabrous, adaxial surfaces glabrous or sparsely pilose, margins usually smooth, sometimes slightly scabrous, apices attenuate. Panicles 10-40 cm, with 3-25 branches, often partially enclosed in the uppermost sheath; branches 5-15 cm, loosely appressed, not twisted, more or less equally subremote to moderately imbricate throughout the panicle, axes often prolonged beyond the distal spikelets, with 10-30 spikelets. Spikelets 8-14 mm, straight, usually divergent, more or less equally imbricate on all the branches. Glumes straight, sides usually glabrous, sometimes pilose near the base or appressed pubescent, hairs to 0.3 mm; lower glumes 4-10 mm, acute; upper glumes 8-14 mm, keels glabrous, lateral veins not present, apices acuminate to obtuse, occasionally apiculate; lemmas glabrous or sparsely pilose, apices usually acuminate; paleas slightly exceeding the lemmas, thin, papery, apices obtuse or rounded; anthers 3-6 mm. 2n = 62.

Distribution

The native range of S. alterniflora is the Atlantic and Gulf Coasts of the United States. It forms the dominant salt-marsh community in salt water, normally forming monoculture meadows where conditions allow.

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

The initial date and method of S. alterniflora introduction to the West (Pacific) coastline is disputed. Sayce (1988) suggests that S. alterniflora was introduced to Willapa Bay, WA, as a discarded packaging material for shipments of eastern oyster spats originating from the east coast of North America. Initially, the species established on the west side of Long Island (Sayce, 1988). However, Cohen and Carlton (1995) have suggested that the earliest report of S. alterniflora occurred around 1911, suggesting that solid ballast material is the most likely transport mechanism. Irrespective of the initial means of introduction, the plant was not accurately identified until 1940s, when the plants flowered (Scheffer, 1945; Sayce, 1988). The clumps, which covered several hectares at that time, had first been noted around 1911 (Scheffer, 1945). During the first 50 years, the population slowly expanded, but from 1945 to 1988 the plant became established throughout the bay, forming vast meadows (Sayce, 1988). After nearly a century of expansion the initial infestation in Willapa Bay spread to a maximum extent of 3500 hectares in 2003. Recent control methods, during 2005/6 have notably reduced the extent of the Willapa population (Murphy et al., 2007). In Puget Sound, WA, S. alterniflora was introduced to stabilize coastlines and increase the vegetative cover of mudflats to reduce wave impact. The Dike Island Gun Club planted S. alterniflora in Padilla Bay in the 1940s to stabilize an island in the south bay. S. alterniflora was also introduced to Thorndyke Bay, Kala Point, and Sequim Bay to increase vegetative cover (Ebasco Environmental, 1992).

In California, S. alterniflora is found at multiple sites in the San Francisco Bay, mostly concentrated in the southern part of the bay (Callaway and Josselyn, 1992; Cohen and Carlton, 1995). A small population was eradicated from Humbolt Bay. Also present in Bolinas Lagoon and the bays of Point Reyes National Seashore, north of San Francisco, where it is being smothered or dug out (Howard, 2008).

Non-indigenous populations of S. alterniflora are also documented in Australia, New Zealand, China, France, the Netherlands and United Kingdom.

Introductions

Risk of Introduction

S. alterniflora can spread via seed dispersal or vegetative fragments. This means that the introduction of S. alterniflora to an estuary or coastline can occur via either natural spread, due to tidal conditions or via human induced actions such as shipping (ballast water) or intentional planting (e.g. San Francisco Bay). S. alterniflora has also been reportedly used as a packing material for oyster shipments. Discarded material could have resulted in the initial invasion of this species from the east to west coast of United States of America (Sayce, 1988).

Habitat

S. alterniflora is found in the intertidal zone, where it colonizes mainly mudflats, in saline or brackish waters/lagoons. It prefers locations with low to moderate wave energy, where it further decreases the wave energy causing sediment to be deposited around its stems. S. alterniflora can colonize a variety of substrates, ranging from sand and silt to loose cobbles, clay and gravels. It also has the capacity to tolerate a wide range of environmental conditions, including: inundation up to approximately 12 hours a day, pH levels between 4.5and 8.5 and salinity levels of 10-60 ppt, although 10-20 ppt allows for optimal growth (Landin, 1991).

Habitat List

Biology and Ecology

Reproductive Biology

S. alterniflora is a long-lived perennial that can reproduce both sexually and by vegetative fragmentation. Daehler and Strong (1994) conducted a self-pollinating experiment to show that S. alterniflora outcrosses, with all self-pollinated seeds failing to germinate. Inflorescences, which are thought to be wind pollinated, develop in August through to October and typically consist of numerous spikelets. Each spikelet contains one seed (Moberley, 1956; Daehler and Strong, 1994). Dormant seeds do not survive longer than one year (Woodhouse, 1979). However, in several areas where the S. alterniflora has been introduced it does not produce seed. No flowers have been observed in New Zealand or in Padilla Bay, and reports on the Willapa Bay population show that it did not flower for almost 50 years after its introduction (Scheffer, 1945; Partridge, 1987; Riggs, 1992; Kunz and Martz, 1993). Low soil temperature can suppress or delay flowering period and reduce seed production in Spartina. Since the waters of the Washington coast are cooler than those in the species’ native Eastern American range, temperature may regulate flowering and seed production (Ebasco Environmental, 1992).

S. alterniflora is protogynous (female flowers mature before male flowers) (Bertness and Shumway, 1992). This strategy helps ensure outcrossing. Since the S. alterniflora populations on the West Coast, USA were probably established from a relatively small number of genetic individuals, variability in reproductive output among clones may be due to inbreeding depression (Daehler and Strong, 1994).

Associations

S. alterniflora is the larval host and/or the nectar source of Automeris louisiana (Louisianan eyed silk moth) (Covell, 2005).

Climate

Latitude/Altitude Ranges

Natural enemies

Impact Summary

Environmental Impact

Impact on Habitats 

Within its introduced range a concern is being raised over S. alterniflora impact to habitats where present due to its ability to reduce tidal energy and trap sediment. On the East and Gulf native coastal ranges, where S. alterniflora is a major component of salt marsh vegetation, wave energy is high, however the presence of S. alterniflora allows for sediment accretion rates of 13 mm/year, with higher stem densities resulting in higher sediment deposition rates and steeper beach profiles (Gleason et al., 1979; Simenstad and Thom, 1995). Where S. alterniflora has been introduced to San Francisco Bay, sediment accretion rates have been estimated at 1.4 to 13.3 mm/yr. (Callaway, 1990; Josselyn et al., 1993; Simenstad and Thom, 1995). In contrast, a study of low intertidal salt marshes in Washington and Oregon that lacked S. alterniflora found that the sediment accretion rate ranged from 2.3 to 6.6 mm/year, with a mean of 3.6 mm/year. (Thom, 1992). This higher rate of accretion rate associated with Spartina may change the fundamental nature of portions of Washington’s coastline. Before S. alterniflora was present, Pacific Northwest estuaries consisted of bare, gently sloping mud flats with shallow tidal channels. Fully developed Spartina marshes have steeply sloping seaward edges and deep, steep-sided tidal channels. S. alterniflora clones trap sediment, causing the clones to rise above the surrounding mudflats (Ebasco Environmental, 1992). Higher stem densities dissipate more wave action, therefore allowing a larger amount of sediment to be deposited and a steeper beach profile to form (Gleason et al., 1979).

Another impact of increased sediment accretion is the resultant change in water circulation patterns. Using a close relative of S. alterniflora as a guide, sediment accretion associated with S. anglica infestations in England, has been reported to reduce tidal flow (Hubbard, 1965). In addition, if large, dense populations of S. alterniflora are present around the mouth of an estuary, decreased flow may occur, leading to an increase in flooding likelihood, especially during sustained periods of heavy rainfall coinciding within above average tides (Ebasco Environmental, 1993).

Impact on Biodiversity

The spread of S. alterniflora can impact the native flora and fauna of the intertidal zone. Spartina may displace native plants, such as Zosteramarina (seagrass), Salicornia virginica, Triglochin maritimum, Jaumea carnosa, and Fucus distichus (Wiggins and Binney, 1987; Simenstad and Thom, 1995). Displacement of several of these plants is of particular concern. For example, seagrasses (Zostera spp.), provides important refuges and food sources for fish, crabs, waterfowl, and other marine life (Balthuis and Scott, 1993).

Other concerns include the replacement of open mudflat habitats associated with bottom-dwelling invertebrate communities by vegetative salt marsh species. Experimental evidence indicates that invertebrate populations in the sediments of S. alterniflora clones, in Willapa Bay are smaller than populations in surrounding non-vegetated intertidal mudflats (Norman and Patten, 1994). The loss of habitat for bivalves is of particular concern in Willapa Bay, WA, as it supports a US$16 million oyster industry. Waders and waterfowl will lose important foraging and refuge habitat. In Willapa National Wildlife Refuge, S. alterniflora has already displaced an estimated 16-20 percent of critical habitat for wintering and breeding aquatic birds (Foss, 1992).

Threatened Species

Risk and Impact Factors

• Invasive in its native range
• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Benefits from human association (i.e. it is a human commensal)
• Long lived
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Reproduces asexually

• Damaged ecosystem services
• Ecosystem change/ habitat alteration
• Modification of hydrology
• Modification of natural benthic communities
• Modification of nutrient regime
• Modification of successional patterns
• Monoculture formation
• Negatively impacts agriculture
• Negatively impacts cultural/traditional practices
• Negatively impacts livelihoods
• Negatively impacts aquaculture/fisheries
• Negatively impacts tourism
• Reduced amenity values
• Reduced native biodiversity
• Soil accretion
• Threat to/ loss of native species
• Transportation disruption

• Competition - monopolizing resources
• Competition - shading
• Competition - smothering
• Hybridization
• Pollen swamping
• Rapid growth
• Rooting

• Highly likely to be transported internationally accidentally
• Difficult/costly to control

Uses

In its native habitat, S. alterniflora is of great value (Landin, 1991; Simenstad and Thom, 1995). The species is extremely productive, exporting approximately 1300 g/m² of detritus annually to the estuarine system (Landin, 1991). Within its native range, S. alterniflora became highly regarded as an erosion control tool, which led to it being widely introduced to other areas (Simenstad and Thom, 1995). Within its native habitat, S. alterniflora roots and shoots are a food source for waterfowl and wetland mammals, partly keeping the expansion of Spartina wetlands in check. In addition, stands of S. alterniflora can serve as a nursery area for mangroves, and estuarine fish and shellfish.

Because of their ability to trap sediment via decreasing wave energy, Spartina species have been introduced to many parts of the world for estuary reclamation and for erosion control (Partridge, 1987). Normally S. anglica has been used for this purpose, however, S. alterniflora has been planted in some areas, such as the North Island of New Zealand (Partridge, 1987).

There are also some economically beneficial uses for S. alterniflora. The species is palatable to livestock, especially deer and horses, so the plant’s continued spread may increase available pasture. S. alterniflora has also been investigated for use within the paper production industry (Ebasco Environmental, 1993).

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control 

Roberts and Pullin (2006; 2007) have, using systematic review and meta-analysis, extensively reviewed the efficacy of the control methods available for S. alterniflora. Within the appendix of their 2006 report, they summarise the individual results of each disparate study and combine these within a meta-analysis to establish the most efficacy control method and attempt to obtain variables (e.g. inundation time, substrate) that might affect the outcomes of each control method. The table below shows the average S. alterniflora density reductions achieved by various control methods. 

The effectiveness of control methods at reducing the densities of S. alterniflora (Roberts and Pullin, 2006)

Physical/mechanical control

On a small scale seedlings can be pulled out. Care must be taken to remove both the shoot and root for effective control. However, seedlings generally begin to tiller late in their first session. Once tillered, hand-pulling may break off portions of the root, allowing the plant to re-grow. Repeated hand-pulling of small plants will eventually result in their death (Spartina Task Force, 1994).

Cutting alone is an effective control intervention of S. alterniflora, producing, on average, an overall decease in stem density of 68.1%. In addition, when a cutting treatment is combined with application of glyphosate (after cutting), S. alterniflora control is vastly improved to 91.1% (Roberts and Pullin, 2006). No experimental trials of combining cutting and smothering are reported for control of S. alterniflora. which proved to be a highly effective control against another cordgrass species S. anglica, achieving around 98%.

Mechanical control interventions against S. alterniflora have been extensively trailed by Dr. Kim Patten on the Willapa Bay populations. Winter tilling produced the most effective control intervention, followed by disking and finally crushing. Crushing effectiveness was affected by the substrate type, with greatest control achieved on sand and soft silt, and least effective on firm silts or those areas with well established Spartina meadows. Based on bird usage and sediment softness, tilling appears to restore mudflats back to suitable habitat for foraging shoreline birds (Gross-Custard and Moser, 1988).

Unfortunately, tilling might be considered too costly for most Spartina management programmes, with the purchase of an amphibious tiller (around £150,000), and is slow to implement (approximately 0.25 ha/hr reported by Patten (2004). Crushing is less expensive than (approximately £50,000), and in addition is quicker than tilling (1-2hr/ha), but for more effective control two or more treatments are required in one year (Roberts and Pullin, 2006; 2007).

Movement control

The movement of Spartina is prohibited in most states of USA. It is also a notified weed, with legislation controlling its movement and planting in New Zealand, Australia, France and the Netherlands. 

Biological control

The use of Prokelisia spp. was shown to be an ineffective sole biological control agent against S. alterniflora, achieving a density reduction in stems of 18.4%. However, further investigation is required to see if integrating it with another control measure would increase its efficacy of controlling S. alterniflora.

Chemical control

The majority of trials captured by Roberts and Pullin (2006) review of Spartina control investigated the impact of either glyphosate or imazapyr. Limited numbers of trials were available for Fenuron, Paraquat, 2,2-DPA and Diuron. The density reductions achieved by the herbicides are included in the table of control measures.

From all the data captured for herbicide application, imazapyr, had the greatest impact in chemically controlling S. alterniflora densities (85% density decline). Lowerconcentrations of the herbicides active ingredient (ae) (1.7kg ae/ha) were required to achieve superior densityreductions than treating with glyphosate (38kg ae/ha). The addition of a surfactant/wetting agentincreased the imazapyr effectiveness at binding to the Spartina stands (Patten, 2002; Roberts and Pullin, 2006).

Control of S. alterniflora densities with glyphosate gave a combined density reduction of around 59%. Roberts and Pullin (2006) results showed there was a great deal of inconsistency (heterogeneity) within the datasets included in their meta-analysis. Further investigation of the differing methods of application used to apply glyphosate showed that aerial application did not significantly reduce the density of S. alterniflora. However, ground sprayed glyphosate did significantly reduce S. alterniflora density, with treatment dates of June/July applications of 38 kg ae/ha being more effective than either similar concentrations at different times of the year or lower active ingredient concentrations. Multiple years of application only marginally increased the herbicides effectiveness, however if a years application is missed then reduction in density drops below 50%. The use of 1-5% wetter or surfactant with the glyphosate application improved the impact of treatment (Norman and Patten, 1995; Patten, 2002; Roberts and Pullin, 2006).

Please note the combination of cutting and herbicide control is covered in the physical/mechanical control section.

Gaps in Knowledge/Research Needs

Further investigation is required to establish the efficacy of the herbicides fenuron, Paraquat™, 2,2-DPA and diuron against S. alterniflora prior to their recommendation for widespread use. In addition the use of Prokelisia spp. could be investigated further as part of an integrated control programme.

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Contributors

12/05/08 Original text by:

Philip Roberts, CABI, Nosworthy Way, Wallingford, Oxon OX10 8DE, UK

Distribution Maps