Exotic Spartina alterniflora provides compatible habitats for native estuarine crab Sesarma dehaani in the Yangtze River estuary

Although the impact of plant invasions on benthic communities, especially burrowing crabs, has received increasing attention, the results from past studies are mixed. The exotic plant Spartina alterniflora has become the most abundant species in the salt marshes of the Yangtze River estuary since it was first found just over a decade ago, but its effects on crabs in the salt marshes is largely unknown. To examine whether the invasions of this exotic plant affected native crabs, we compared the biomass and abundance of the dominant burrowing crab Sesarma dehaani in an exotic Spartina marsh, native Phragmites australis marsh and mudflats of the Yangtze River estuary, China. To explain the differences of S. dehaani populations between different habitats, feeding preference of S. dehaani for Spartina and Phragmites was investigated. Results showed crab abundance and biomass in the Spartina marsh were significantly greater than those in the Phragmites marsh and mudflats. Soil water content and plant community characteristics in the Spartina marsh also significantly differed in the Phragmites marsh and mudflats. Moreover, the feeding preference experiment showed that crabs consumed Spartina more than twice as much as Phragmites. In summary, this study showed that Spartina provided compatible habitats for native crab S. dehaani through offering suitable food source and moderate environmental conditions.     

Growth,survival, and metal content of marsh invertebrates fed diets of detritus from Spartina alterniflora Loisel. and Phragmites australis Cav. Trin. ex Steud. from metal-contaminated and clean sites

Marsh vegetation plays an important role in trophic ecology of estuaries. Once broken down to detritus, it is an important food source for manyorganisms. In Atlantic Coast marshes, the reed Phragmites australis hasbeen invading many areas once dominated by smooth cordgrass, Spartina alterniflora. In this study we evaluated the growth of and trophictransfer of metals to estuarine invertebrates when fed diets of detritus fromthese different plant species. Decaying leaves from populations of Phragmites, natural Spartina, and restored Spartina from boththe Hackensack Meadowlands, New Jersey, and the more pristineAccabonac Harbor of East Hampton, New York, were collected from themarsh surface in the spring. Decaying leaves were pureed and fed to thefiddler crabs Uca pugnax and U. pugilator, and to the grassshrimp Palaemonetes pugio. In fiddler crabs we monitored limbregeneration, molting and weight. U. pugilator regenerated limbs andmolted equally well on all six diets. Most of the U. pugnax arrestedgrowth midway through regeneration on all 6 diets. A repeat experimentwith smaller crabs, which did complete the process, found no consistentdifferences among the six diets and control food, although control food andPhragmites detritus had higher N concentrations than the Spartinadetritus. Grass shrimp fed all six diets did not survive beyond 3 weeks. Inanother experiment using HM sediments from each vegetation type(containing detritus, meiofauna, and microflora), survival was equally highamong treatments and the shrimp fed sediments from the restored Spartina site or control food grew better than those fed sediments fromthe Phragmites or natural Spartina sites. Although metalconcentrations in detritus varied between sites and plant species, the crabsof each group did not differ in metal concentrations after the feedingexperiment. Our data do not support the general assumption that Phragmites leaf detritus is of poorer nutritional quality than Spartinaalterniflora leaf detritus to estuarine consumers.     

Effects of saltmarsh invasion by Spartina alterniflora on arthropod community structure and diets

Invasive plants strongly affect physical and biotic environments of native ecosystems. Insects and other arthropods as one of the major components of many ecosystems are very sensitive to subtle changes in abiotic and biotic environments. We examined the effects of exotic Spartina alterniflora invasion on community structure and diets of arthropods in a saltmarsh previously dominated by native Phragmites australis in Yangtze River estuary through net sweeping and plant harvesting methods and stable isotope analysis. Our results showed that diversity indices were not significantly different between exotic and native plant communities, but the total abundance of insects estimated through plant harvesting method was found to be lower in Spartina monoculture than that in Phragmites monoculture. Community structure of insects in Spartina monoculture was dissimilar to that in Phragmites monoculture and Phragmites–Spartina mixture. Moreover, stable carbon isotope patterns of arthropods were significantly different between Phragmites and Spartina monocultures. Although some native arthropods (perhaps generalists) shifted their diets, many native taxa did prefer Phragmites to Spartina even in Spartina monoculture. Spartina invasions resulted in reduced abundances of some arthropds, and increased dominance of others feeding preferably on Spartina. This study provides evidence that invasive plants can change the community structure and diets of native arthropods, which will eventually alter the arthropod food web, and affect the integrity and functioning of native ecosystems within a nature reserve that has been set aside for conserving the native biodiversity and maintaining the ecosystem integrity. In this sense, Spartina invasions in the Yangtze River estuary need to be managed appropriately.     

A comparison of Phragmites australisin freshwater and brackish marsh environments in North America

This paper compares the available North Americanliterature and data concerning several ecologicalfactors affecting Phragmites australisin inlandfreshwater, tidal fresh, and tidal brackish marshsystems. We compare aboveground productivity, plantspecies diversity, and sediment biogeochemistry; andwe summarize Phragmiteseffects on faunalpopulations in these habitats. These data suggest thatPhragmitesaboveground biomass is higher thanthat of other plant species occurring in the samemarsh system. Available data do not indicate anysignificant difference in the aboveground Phragmitesbiomass between marsh types, nor doesthere appear to be an effect of salinity on height.However, Phragmitesstem density wassignificantly lower in inland non-tidal freshwatermarshes than in tidal marshes, whether fresh orbrackish. Studies of the effects of Phragmiteson plant species richness suggest that Phragmitesdominated sites have lower diversity.Furthermore, Phragmiteseradication infreshwater sites increased plant diversity in allcases. Phragmitesdominated communities appearto have different patterns of nitrogen cyclingcompared to adjacent plant communities. Abovegroundstanding stocks of nitrogen (N) were found to behigher in Phragmitessites compared to thosewithout Phragmites. Porewater ammonium(NH₄ ⁺) did not differ among plant covertypes in the freshwater tidal wetlands, but inbrackish marshes NH₄ ⁺was much higher inSpartinaspp. than in neighboring Phragmitesstands. Faunal uses of Phragmitesdominated sites in North America were found to vary bytaxa and in some cases equaled or exceeded use ofother robust emergent plant communities. In light ofthese findings, we make recommendations for futureresearch.     

Litter pool sizes,decomposition, and nitrogen dynamics in <Emphasis Type="Italic">Spartina alterniflora</Emphasis>-invaded and native coastal marshlands of the Yangtze Estuary

Past studies have focused primarily on the effects of invasive plants on litter decomposition at soil surfaces. In natural ecosystems, however, considerable amounts of litter may be at aerial and belowground positions. This study was designed to examine the effects of Spartina alterniflora invasion on the pool sizes and decomposition of aerial, surficial, and belowground litter in coastal marshlands, the Yangtze Estuary, which were originally occupied by two native species, Scirpus mariqueter and Phragmites australis. We collected aerial and surficial litter of the three species once a month and belowground litter once every 2 months. We used the litterbag method to quantify litter decomposition at the aerial, surficial and belowground positions for the three species. Yearly averaged litter mass in the Spartina stands was 1.99 kg m⁻²; this was 250 and 22.8% higher than that in the Scirpus (0.57 kg m⁻²) and Phragmites (1.62 kg m⁻²) stands, respectively. The litter in the Spartina stands was primarily distributed in the air (45%) and belowground (48%), while Scirpus and Phragmites litter was mainly allocated to belowground positions (85 and 59%, respectively). The averaged decomposition rates of aerial, surficial, and belowground litter were 0.82, 1.83, and 1.27 year⁻¹ for Spartina, respectively; these were 52, 62 and 69% of those for Scirpus litter at corresponding positions and 158, 144 and 78% of those for Phragmites litter, respectively. The differences in decomposition rates between Spartina and the two native species were largely due to differences in litter quality among the three species, particularly for the belowground litter. The absolute amount of nitrogen increased during the decomposition of Spartina stem, sheath and root litter, while the amount of nitrogen in Scirpus and Phragmites litter declined during decomposition for all tissue types. Our results suggest that Spartina invasion altered the carbon and nitrogen cycling in the coastal marshlands of China.     

Utilization of a citizen monitoring protocol to assess the structure and function of natural and stabilized fringing salt marshes in North Carolina

Narrow fringing salt marshes dominated by Spartina alterniflora occur naturally along estuarine shorelines and provide many of the same ecological functions as more extensive marshes. These fringing salt marshes are sometimes incorporated into shoreline stabilization efforts. We obtained data on elevation, salinity, sediment characteristics, vegetation and fish utilization at three study sites containing both natural fringing marshes and nearby restored marshes located landward of a stone sill constructed for shoreline stabilization. During the study, sediment accretion rates in the restored marshes were approximately 1.5- to 2-fold greater than those recorded in the natural marshes. Natural fringing marsh sediments were predominantly sandy with a mean organic matter content ranging between 1.5 and 6.0%. Average S. alterniflora stem density in natural marshes ranged between 130 and 222 stems m⁻², while mean maximum stem height exceeded 64 cm. After 3 years, one of the three restored marshes (NCMM) achieved S. alterniflora stem densities equivalent to that of the natural fringing marshes, while percentage cover and maximum stem heights were significantly greater in the natural than in the restored marshes at all sites. There was no significant difference in the mean number of fish, crabs or shrimp captured with fyke nets between the natural and restored marshes, and only the abundance of Palaemonetes vulgaris (grass shrimp) was significantly greater in the natural marshes than in the restored ones. Mean numbers of fish caught per 5 m of marsh front were similar to those reported in the literature from marshes adjacent to tidal creeks and channels, and ranged between 509 and 634 fish net⁻¹. Most of the field data and some of the sample analyses were obtained by volunteers as they contributed 223 h of the total 300 h spent collecting data from three sites in one season. The use of fyke nets required twice as many man-hours as any other single task. Vegetation and sediment parameters were sensitive indicators of marsh restoration success, and volunteers were capable of contributing a significant portion of the labor needed to collect these parameters. The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Evaluation of Long‐Term Response of Intertidal Creek Nekton to Phragmites australis (Common Reed) Removal in Oligohaline Delaware Bay Salt Marshes

In the oligohaline Alloway Creek watershed of the upper Delaware Bay, invasive Phragmites australis (Common reed; hereafter Phragmites) has been removed in an attempt to restore tidal marshes to pre‐invasion form and function. In order to determine the effects of Phragmites on nekton use of intertidal creeks and to evaluate the success of this restoration, intertidal creek nekton assemblages were sampled with weirs from May to November for 7 years (1999‐2005) in three marsh types: natural Spartina alterniflora (Smooth cordgrass; hereafter Spartina), sites treated for Phragmites removal (hereafter referred to as Treated), and invasive Phragmites marshes. Replicate intertidal creek collections in all three marsh types consisted primarily of resident nekton and were dominated by a relatively low number of ubiquitous intertidal species. The Treated marsh nekton assemblage was distinguished by greater abundances of most nekton, especially Fundulus heteroclitus (Mummichog). Phragmites had little impact on nekton use of intertidal creeks over this period as evidenced by similar nekton assemblages in the Spartina and Phragmites marshes for most years. Long‐term assemblage‐level analyses and nekton abundances indicated that the Treated marsh provided enhanced conditions for intertidal creek nekton. The response of intertidal creek nekton suggests that the stage of the restoration may influence the results of comparisons between the marsh types and should be considered when evaluating marsh restorations.     

Interactions between the grass shrimp <Emphasis Type="Italic">Palaemonetes pugio</Emphasis> and the salt marsh grasses <Emphasis Type="Italic">Phragmites australis</Emphasis> and <Emphasis Type="Italic">Spartina alterniflora</Emphasis>

The grass shrimp Palaemonetes pugio, a species common to Spartina alterniflora-dominated marshes, may be sensitive to the invasion of the common reed Phragmites australis in northeastern US salt marshes. We examined two questions: (1) Do grass shrimp have a preference for the native plant over the non-native plant? (2) Are grass shrimp more effective foragers on P. australis? We tested the first hypothesis by comparing the amount of time shrimp spend in physical contact with the plant types over a 1-h period. Shrimp were observed under different arrangements of vegetation to control for differences in conspicuous structural features. Additionally, the amount of time shrimp spent foraging on S. alterniflora and P. australis shoots was compared to determine if shrimp graze more often on S. alterniflora. Shrimp spent significantly more time in contact with S. alterniflora only when plant types were grouped at opposite ends of aquaria, but did not exhibit a foraging preference for this plant type. To address our second question, we investigated the effects of shrimp foraging on stem epifauna, an assemblage of semi-aquatic invertebrates associated with macrophyte shoots. Previous research showed that P. australis supports a lower density of stem-dwelling epifauna relative to S. alterniflora. We hypothesized that the primary grazer of this community, P. pugio, can forage on P. australis stems more effectively due to structural differences between the two plants, causing the lower abundance of epifauna through top-down effects. We exposed individual shoots inhabited by epifauna to shrimp and compared faunal densities on exposed shoots to densities on control shoots after 18 h. The reduction of epifauna by predation was proportional on the two plant types. Therefore, top-down effects can be ruled out as an explanation for the patchy distribution of epifauna observed in P. australis–S. alterniflora marshes.     

Restoration of Arthropod Assemblages in a Spartina Salt Marsh following Removal of the Invasive Plant Phragmites australis

Invasive plants are one of the most serious threats to native species assemblages and have been responsible for the degradation of natural habitats worldwide. As a result, removal of invasive species and reestablishment of natural vegetation have been attempted in order to restore biodiversity and ecosystem function. This study examined how native arthropod assemblages, an abundant and functionally important group of organisms in many ecosystems, are affected by the incursion of the invasive wetland plant Phragmites australis and if the restoration of the native vegetation in brackish Spartina alterniflora marshes results in the reestablishment of the arthropod community. The invasion of Phragmites into a coastal Spartina marsh in southern New Jersey seriously altered arthropod assemblages and trophic structure by changing the abundance of trophic groups (detritivores, herbivores, carnivores) and their taxonomic composition. Herbivore assemblages shifted from the dominance of external free‐living specialists (e.g., planthoppers) in Spartina to concealed feeders in Phragmites (stem‐feeding cecidomyiids). Moreover, free‐living arthropods in Phragmites became dominated by detritivores such as Collembola and chironomids. The dominant marsh spiders, web‐building linyphiids, were significantly reduced in Phragmites habitats, likely caused by differences in the physical environment of the invaded habitats (e.g., lower stem densities). Thus, trophic structure of arthropod assemblages in Phragmites, as seen in the large shifts in feeding guilds, was significantly different from that in Spartina. Removal of Phragmites with the herbicide glyphosate resulted in the rapid return of Spartina (≤5 yrs). Moreover, return of the dominant vegetation was accompanied by the recovery of most original habitat characteristics (e.g., live and dead plant biomass, water flow rate). The arthropod assemblage associated with Spartina also quickly returned to its preinvasion state and was not distinguishable from that in uninvaded Spartina reference sites. This study provides evidence that the reestablishment of native vegetation in areas previously altered by an invasive plant can result in the rapid recovery of the native arthropod assemblage associated with the restored habitat.     

Invasion of <Emphasis Type="Italic">Spartina alterniflora</Emphasis> Enhanced Ecosystem Carbon and Nitrogen Stocks in the Yangtze Estuary,China

Whether plant invasion increases ecosystem carbon (C) stocks is controversial largely due to the lack of knowledge about differences in ecophysiological properties between invasive and native species. We conducted a field experiment in which we measured ecophysiological properties to explore the response of the ecosystem C stocks to the invasion of Spartina alterniflora (Spartina) in wetlands dominated by native Scirpus mariqueter (Scirpus) and Phragmites australis (Phragmites) in the Yangtze Estuary, China. We measured growing season length, leaf area index (LAI), net photosynthetic rate (Pn), root biomass, net primary production (NPP), litter quality and litter decomposition, plant and soil C and nitrogen (N) stocks in ecosystems dominated by the three species. Our results showed that Spartina had a longer growing season, higher LAI, higher Pn, and greater root biomass than Scirpus and Phragmites. Net primary production (NPP) was 2.16 kg C m⁻² y⁻¹ in Spartina ecosystems, which was, on average, 1.44 and 0.47 kg C m⁻² y⁻¹ greater than that in Scirpus and Phragmites ecosystems, respectively. The litter decomposition rate, particularly the belowground decomposition rate, was lower for Spartina than Scirpus and Phragmites due to the lower litter quality of Spartina. The ecosystem C stock (20.94 kg m⁻²) for Spartina was greater than that for Scirpus (17.07 kg m⁻²), Phragmites (19.51 kg m⁻²) and the mudflats (15.12 kg m⁻²). Additionally, Spartina ecosystems had a significantly greater N stock (698.8 g m⁻²) than Scirpus (597.1 g m⁻²), Phragmites ecosystems (578.2 g m⁻²) and the mudflats (375.1 g m⁻²). Our results suggest that Spartina invasion altered ecophysiological processes, resulted in changes in NPP and litter decomposition, and ultimately led to enhanced ecosystem C and N stocks in the invaded ecosystems in comparison to the ecosystems with native species.     

Effects of environmental gradients on the performances of four dominant plants in a Chinese saltmarsh: implications for plant zonation

Physical conditions and biotic interactions are believed to be the determinants of plant zonation in saltmarshes. However, in rapidly developing estuarine marshes, succession is regarded as the primary process responsible for plant zonation and it is controlled mainly by environmental factors. Salinity and inundation are two important factors responsible for the distribution pattern of dominant plants in coastal saltmarshes. Here we conducted a common garden experiment as well as a field transplanting to examine the responses of four dominant saltmarsh plants (native Scirpus mariqueter, Scirpus triqueter and Phragmites australis, and exotic Spartina alterniflora) in the Yangtze River estuary to environmental gradients, which may help us understand their current and potential zonation. The results showed that Scirpus adapted to freshwater and less inundated habitats, Phragmites performed well in brackish or freshwater environments with less inundation, and Spartina tolerated the highest salinity and deepest inundation. In the harshest environments (the highest salinity and water level), only Spartina performed well. In the mild environments, however, there were only minor differences in the performances among the four species. The potential ranges of Phragmites and Spartina were predicted to be larger than their current ones, and their lower boundaries might be set by tidal scour rather than edaphic factors. With the saltmarsh succession, invasive Spartina in the Yangtze River estuary might ultimately replace Scirpus, and alter the zonal patterns of native saltmarsh plants, which will lead to severe ecosystem consequences. Thus, proper management measures (e.g., repeated mowing) need to be implemented to control this invasive exotic plant, and restore the vulnerable ecosystems invaded by Spartina in the Yangtze River estuary.     

Plant diversity in Lythrum,Phragmites, and Typhamarshes,Massachusetts, U.S.A.

Concern about colonization of marshesby plant species such as Phragmites australisand Lythrum salicariahas highlighted the needfor management strategies. However, there is a lack ofinformation in the literature on which to base thesedecisions. This study compares the alpha diversity ofmarshes to assess the impact of invasion by Phragmitesand Lythrum. Species occurrence andstem density were measured in marshes dominated by Phragmites, Lythrum, Typhaspp., or otherherbaceous perennials in the Charles River watershedin eastern Massachusetts, USA, and species richness,Shannon's H, Simpson's reciprocal (1/D), and Pielou'sJ were compared among six community types. The threediversity indices had significantly higher values forTypha-Lythrummarshes than for any of the othermarsh types (Tukey test, p< 0.05), with mean values(± s.d.) of H = 2.00 ± 0.74, 1/D = 3.51± 1.68 and J = 0.69 ± 0.1. Marshes dominatedby Phragmiteshad the lowest diversity, with H= 0 and D = 1, i.e. they were monospecific. Typhadominated marshes had the second lowest values,with H = 0.17 ± 0.05, 1/D = 1.05 ± 0.01, andJ = 0.11 ± 0.03. These results support the ideathat a reduction in diversity can be expected inmarshes colonized by Phragmites. However, thehigh diversity found in the Typha-Lythrummarshes contradicts the expectation of lower diversityafter invasion by Lythrum. This information mayalter marsh management decisions.     

Modification of Sediments and Macrofauna by an Invasive Marsh Plant

Invasive grasses have recently altered salt marsh ecosystems throughout the northern hemisphere. On the eastern seaboard of the USA, Phragmites australis has invaded both brackish and salt marsh habitats. Phragmites australis influence on sediments and fauna was investigated along a salinity and invasion-age gradient in marshes of the lower Connecticut River estuary. Typical salinities were about 19–24 ppt in Site I, 9–10 ppt in Site II and 5–7 ppt in Site III. Strongest effects were evident in the least saline settings (II and III) where Phragmites has been present the longest and exists in monoculture. Limited influence was evident in the most saline region (I) where Phragmites and native salt marsh plants co-occur. The vegetation within Phragmites stands in tidal regions of the Connecticut River generally exhibits taller, but less dense shoots, higher above-ground biomass, and lower below-ground biomass than does the un-invaded marsh flora. There were lower sediment organic content, greater litter accumulation and higher sediment chlorophyll a concentrations in Phragmites- invaded than un-invaded marsh habitat. Epifaunal gastropods (Succinea wilsoni and Stagnicola catascopium) were less abundant in habitats where Phragmites had invaded than in un-invaded marsh habitat. Macro-infaunal densities were lower in the Phragmites-invaded than un-invaded habitats at the two least saline sites (II and III). Phragmites stands supported more podurid insects, sabellid polychaetes, and peracarid crustaceans, fewer arachnids, midges, tubificid and enchytraeid oligochaetes, and greater habitat-wide taxon richness as measured by rarefaction, than did the un-invaded stands. The magnitude and significance of the compositional differences varied with season and with site; differences were generally greatest at the oldest, least saline sites (II and III) and during May, when faunal densities were higher than in September. However, experimental design and the 1-year study period precluded clear separation of salinity, age, and seasonal effects. Although structural effects of Phragmites on salt marsh faunas are evident, further investigation is required to determine the consequences of these effects for ecosystem function. This revised version was published online in July 2006 with corrections to the Cover Date.     

Native and Introduced Ecosystem Engineers Produce Contrasting Effects on Estuarine Infaunal Communities

Cordgrasses in the genus Spartina are good examples of ecosystem engineers that modify habitat structure in estuaries throughout the world. In San Francisco Bay, California, USA, marshes containing native California cordgrass (Spartina foliosa) are being invaded by a hybrid (S. alterniflora × S. foliosa) formed after introduction of S. alterniflora. This study compared vegetation, sediment structure, and infaunal invertebrates in native and invaded marshes. We hypothesized that differences in the physical structure between S. foliosa and hybrid Spartina would be reflected in differences in density, biomass, diversity, and taxonomic composition of infauna. Hybrid Spartina modifies habitat structure more than S. foliosa by producing taller stems, and greater plant biomass both above- and belowground while occupying a much wider tidal range, thereby transforming open mudflats to a vegetated habitat. In general, S. foliosa areas contained significantly higher densities of benthic infauna than adjacent mudflats, while hybrid Spartina areas never contained greater infaunal densities than mudflats. This is because S. foliosa produces a moderate level of structure that can facilitate benthic invertebrates, whereas hybrid Spartina produces so much structure, particularly belowground, that it actually excludes invertebrates. Therefore, we suggest that these two closely related species both act as ecosystem engineers, but with opposing effects on invertebrate communities.     

Dominant environmental factors in wetland plant communities invaded by Phragmites australis in East Harbor, Ohio, USA

Elevation, standing crop, disturbance and soil fertility often emerge from studies of freshwater plant communities as the dominant environmental factors determining both species richness and species composition. Few studies in North America have investigated the relationship between these factors and species abundance (standing crop) and species composition in the context of invasion by Phragmites australis. This study explores the influence of key abiotic and biotic variables on species abundance and composition across three Lake Erie wetlands differing in hydrology and Phragmites abundance in East Harbor, Ohio, USA. Standing crop for 92 species was related to standard sediment analyses, wave exposure, distance to shoreline, elevation, light interference, species density, and Phragmites standing crop in each of 95 1 × 1 m quadrats by using canonical correspondence analysis (CCA). Elevation (Axis I) and Phragmites standing␣crop-soil fertility (Axis II) explained 35.7 and 26.2%, respectively, of the variation in the species–environment relationships. Wave exposure was not a primary component of the first four canonical axes. Axis I was instrumental in describing species composition, separating wet meadow species from marsh species. Axis II was inversely related to species density for both wet meadow and marsh species. These findings generally support prevailing models describing the distribution of wetland plants along environmental gradients. Two discrepancies were noted, however: (1) species density was highest in the most sheltered sites and (2) wave exposure was directly associated with Phragmites standing crop-soil fertility gradient. The structural integrity of Phragmites stems, topographic heterogeneity and differential responses to anthropogenic disturbance may contribute to departure from prevailing multivariate models. This information has direct implications for local and regional wetland managers.     

Spread of Exotic Cordgrasses and Hybrids (Spartina sp.) in the Tidal Marshes of San Francisco Bay, California, USA

Four species of exotic cordgrass (Spartina sp.) occur in the San Francisco estuary in addition to the California native Spartina foliosa. Our goal was to map the location and extent of all non-native Spartina in the estuary. Hybrids of S. alterniflora and S. foliosa are by far the most numerous exotic and are spreading rapidly. Radiating from sites of deliberate introduction, S. alterniflora and hybrids now cover ca. 190 ha, mainly in the South and Central Bay. Estimates of rate of aerial increase range from a constant value to an accelerating rate of increase. This could be due to the proliferation of hybrid clones capable of rapid expansion and having superior seed set and siring abilities. The total coverage of 195 ha by hybrids and other exotic cordgrass species is slightly less than 1% of the Bay's tidal mudflats and marshes. Spartina anglica has not spread beyond its original 1970s introduction site. Spartina densiflora has spread to cover over 5 ha at 3 sites in the Central Bay. Spartina patens has expanded from 2 plants in 1970 to 42 plants at one site in Suisun Bay. Spartina seed floats on the tide, giving it the potential to export this invasion throughout the San Francisco estuary, and to estuaries outside of the Golden Gate. We found isolated plants of S. alterniflora and S. densiflora in outer coast estuaries north of the Bay suggesting the likelihood for the San Francisco Bay populations to found others on the Pacific coast.     

Effects of grazing and inundation on pasture quality and seed production in a salt marsh

During a six-year period, changes in the composition of dominant plant species of importance to foraging birds in a salt marsh on the Swedish west coast were followed inside and outside exclosures to document effects of grazing on herbage quality and seed production. Since marshes provide an important habitat for foraging geese and ducks, it was of interest to determine how cattle grazing would affect herbage production inAgrostis stolonifera andPuccinellia maritima and seed and root-tuber production inScirpus maritimus. Measurements of cover and height in permanent plots revealed that a wetter weather type favouredAgrostis, probably through reduced salinity, at the expense ofPuccinellia, which was the most favoured food of both cattle and birds.Agrostis out-competedPuccinellia when grazing pressure was low. Seed production inScirpus maritimus was reduced by cattle grazing, particularly whenPhragmites australis formed part of the vegetation. In the absence of cattle grazing, both herbage- and seed producing plants were gradually reduced, andPhragmites increased. Since high herbage consumption and high seed production are mutually exclusive, grazing rotation in combination with mowing is suggested as a management strategy.     

Response of <Emphasis Type="Italic">Phragmites</Emphasis> to environmental parameters associated with treatments

This multi-year study evaluated the response of invasive Phragmites australis to changes in pore water geochemistry associated with tidal enhancement, alone or in combination with other prescribed management regimes used by the US Fish and Wildlife Service. A pilot study was conducted prior to the treatment experiment that showed a negative correlation between the growth of Phragmites and cation concentrations in a transitional vegetation zone. In the targeted 535-acre brackish-water impoundment (East Pool) where Phragmites dominated, the soil water chemistry was changed by introducing tidal salt water through water control structures in June of 1999. Soil profiles, pH, salinity and cation concentration data in addition to Phragmites height and density data were collected both before and after the treatments were imposed, where possible. It was generally observed that a soil water salinity above ∼28 would be needed to maintain the reduction of Phragmites and to support its replacement by salt marsh species. In the tidal water manipulated experimental macroplots, the soil water salinity changed from 7.1 to 32 on average between 1999 and 2001. The reduction of the average height of Phragmites ranged from 25% to 84% for different treatment combinations, while untreated sites exhibited a slight increases in height. The reduction in average live density ranged from 51% to 87% for different treatment combinations. The greatest reduction of Phragmites density and height resulted when tidal enhancement was followed by a prescribed burn in the winter. Also, significant negative correlations were observed between Phragmites height and the main cations associated with tidal salt water including Mg²⁺, Na⁺ and K⁺ and to a lesser extent Ca²⁺. pH did not change drastically with the introduction of tidal water over the period of 1999–2001 and did not appear to play a significant role in changing the growth of Phragmites. A reduction of soil adhesiveness associated with the decay of Phragmites roots was observed after a two month period in 2001 when plants were submerged in standing water. This points to the need to maintain tidal exchange to promote a gradual transition from a Phragmites-dominated system to a Spartina-dominated system. Towards the end of the growing season in 2001, Spartina patens and Distichlis spicata had begun to ramify into the center of the island patches.     

Growth of Phragmites australis and Phalaris arundinacea in constructed wetlands for wastewater treatment in the Czech Republic

Common reed (Phragmites australis) and reed canarygrass (Phalaris arundinacea) are two most commonly used plant species in constructed wetlands for wastewater treatment in the Czech Republic. Growth characteristics of both plants (biomass, stem count, and length) have been measured in 13 horizontal sub-surface flow constructed wetlands since 1992. The results revealed that while Phalaris usually reaches its maximum biomass as early as during the second growing season, Phragmites usually reaches its maximum only after three to four growing seasons. The maximum biomass of both species varies widely among systems and the highest measured values (5070 g m⁻² for Phragmites and 1900 g m⁻² for Phalaris) are similar to those found in eutrophic natural stands. The shoot count of Phragmites decreases after the second growing season while length and weight of individual shoots increases over time due to self-thinning process. Number of Phalaris shoots is the highest during the second season and then the shoot count remains about the same. Also the shoot length remains steady over years of constructed wetland operation.     

A Paleoecological Assessment of Phragmites australis in New England Tidal Marshes: Changes in Plant Community Structure During the Last Few Millennia

Although Phragmites has been an upper border tidal marsh species for thousands of years, it is only recently (within the last century or so) that the distribution of this plant within the coastal marsh community has become prominent. Prior to approximately 100 years ago, Phragmites was an upper border/brackish marsh co-dominant in many marsh systems. Occurrence of this species varied between associations of sedges, Typha, forbs and a variety of woody shrubs. Paleoreconstructions rarely show the presence of a Phragmites monoculture or early associations with salt marsh species. However, since the turn of this century (and perhaps as early as the middle of the last century) the distribution of Phragmites has changed substantially. Today, this plant often forms dense monocultures and is commonly found in association with Spartina grasses. The results of this paleoecological investigation show that the changes that have been observed in Phragmites communities during the last 100 years are not part of the long-term cycle of development in these systems and are new to the landscape.