Common Reed Phragmites australis: Control and Effects Upon Biodiversity in Freshwater Nontidal Wetlands

Phragmites australis (common reed) has expanded in many wetland habitats. Its ability to exclude other plant species has led to both control and eradication programs. This study examined two control methods—herbicide application or a herbicide‐burning combination—for their efficacy and ability to restore plant biodiversity in non‐tidal wetlands. Two Phragmites‐dominated sites received the herbicide glyphosate. One of these sites was burned following herbicide application. Plant and soil macroinvertebrate abundance and diversity were evaluated pre‐treatment and every year for four years post‐treatment using belt transects. The growth of Phragmites propagules—seeds, rhizomes, and rooted shoots—was examined in the greenhouse and under bare, burned, or vegetated soil conditions. Both control programs greatly reduced Phragmites abundance and increased plant biodiversity. Plant re‐growth was quicker on the herbicide‐burn site, with presumably a more rapid return to wetland function. Re‐growth at both sites depended upon a pre‐existing, diverse soil seed bank. There were no directed changes in soil macroinvertebrate abundance or diversity and they appeared unaffected by changes in the plant community. Phragmites seeds survived only on bare soils, while buried rhizomes survived under all soil conditions. This suggests natural seeding of disturbed soils and inadvertent human planting of rhizomes as likely avenues for Phragmites colonization. Herbicide control, with or without burning, can reduce Phragmites abundance and increase plant biodiversity temporarily. These changes do not necessarily lead to a more diverse animal community. Moreover, unless Phragmites is eradicated and further human disturbance is prohibited, it will likely eventually re‐establish dominance.     

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.     

Tidal‐flow restoration provides little nesting habitat for a globally vulnerable saltmarsh bird

Tidal marshes are among the most threatened habitats on Earth because of their limited natural extent, a long history of human drainage and modification, and anticipated future sea‐level rise. Tidal marshes also provide services to humans and support species of high conservation interest. Consequently, millions of dollars have been spent on tidal marsh restoration throughout North America. Southern New England has a long history of tidal marsh restorations, often focused on removal of the invasive plant Phragmites australis. Working in 18 Connecticut marshes, we examined the bird community in 21 plots in restoration sites and 19 plots in reference sites. Restoration plots were divided into those in marshes where management involved restoring tidal flow and those where direct Phragmites control (e.g. cutting, herbicide) was used. Saltmarsh sparrows Ammodramus caudacutus, which are considered globally vulnerable to extinction, were less common where tidal flow had been restored than at reference sites and nested in only one of 14 tidal‐flow restoration plots. No abundance differences were found for large wading birds, willets Tringa semipalmata, or seaside sparrows Ammodramus maritimus. Vegetation at sites where tidal flow had been restored showed characteristics typical of lower‐elevation marsh, which is unsuitable for nesting saltmarsh sparrows. We conclude that, although tidal‐flow restorations in Connecticut control Phragmites and restore native saltmarsh vegetation, they produce conditions that are largely unsuitable for one of the highest conservation priority species found in eastern U.S. salt marshes.     

Invasive reed effects on benthic community structure in Lake Erie coastal marshes

We examined how dominance (% canopy cover) and invasion history of common reed, Phragmites australis, affected benthic macroinvertebrate diversity and density in 8 marshes along Lake Erie’s southern shoreline. We also compared macroinvertebrate densities among patches (0.25 m²) of reed, cattail (Typha spp.), and native flora (e.g., Sagittaria, Sparganium) and epiphytic algal communities on submerged stems of reed and cattail. Narrow-leaf cattail (T. angustifolia) is also a common invasive plant to these wetlands, but does not greatly change plant community composition or ecosystem conditions like reed. Macroinvertebrate diversity (Shannon–Weaver H′) was positively related to reed cover and was highest (4.6) in two marshes with ~35- and 5-year invasion histories. Shading from high reed cover increased H′-diversity, in part, by reducing the abundance of floating duckweed, which harbored many Hyalella azteca amphipods. Percent Ephemeroptera, Odonata, and Trichoptera was low to moderate across marshes, regardless of reed cover and invasion history. Macroinvertebrate density was not affected by reed cover or average plant stem density, and did not differ among plant types. However, epiphyton densities and % diatoms were greater on reed than on cattail, suggesting reed provides a better feeding habitat for microalgal grazers than Typha. Abundance rankings of common species in these diatom-dominated communities were also typically dissimilar between these plant types. Although % grazers was unrelated to epiphyton densities and % diatoms, grazer identity (snails) differed between natural and diked marshes, which had different microalgal food supplies. Our findings suggest that Phragmites does not necessarily adversely affect macroinvertebrate community structure and diversity and that invasion history alone has little effect on the H′-diversity–reed dominance relationship.     

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.     

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.     

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.     

Changes inPhragmites australis in south-eastern Australia: A habitat assessment

The status of common reed (Phragmites australis) in south-eastern Australia was assessed by considering its physical habitat.Phragmites habitats were categorized into three types — wetland, riverine and estuarine and all three showed negative change (loss, degradation) since European settlement. However, there were also instances of positive (new, re-establishment) changes. Integrating these negative and positive changes at the catchment scale for the Murrumbidgee River, suggests a re-distribution ofPhragmites is occurring, and this may be true for other rivers managed for irrigation. Agriculture appears to be the principal cause ofPhragmites australis losses in eastern Australia. There is no evidence to date of reed decline in Australia like that in parts of Europe, nor of expansion as in the coastal wetlands of the United States of America. The habitat approach used here was qualitative but this was necessary due to the lack of historical data onPhragmites and to the limited number of case studies. However, quantitative studies are needed, in order to understand how river health and aquatic biodiversity are being affected.     

辽河三角洲河口芦苇沼泽湿地植被固碳潜力

增加陆地生态系统碳汇是一种有效应对CO2浓度升高的措施。河口湿地是一类特殊的陆地生态系统,是生产力最高的生态系统之一。研究河口湿地的固碳潜力对准确评估河口湿地碳汇、发挥和提高湿地固碳功能具有重要意义。通过野外调查和数值模型,量化研究了辽河三角洲河口沼泽湿地的植被固碳潜力。根据区域的实际情况,将植被的固碳潜力分为湿地演替、人工灌溉苇田和气候变化的潜力。研究结果表明辽河三角洲河口沼泽湿地植被具有很高的固碳潜力,翅碱蓬(Suaeda pterantha)群落扩张每年可递增固碳潜力0.053—0.07Gg C,滩涂转变为芦苇(Phragmites australis)沼泽每年可递增固碳潜力0.07Gg C,芦苇、獐毛草甸(Aeluropus sinensis)演替为芦苇沼泽的固碳潜力为17.2 Gg C/a,通过灌溉管理措施,芦苇沼泽的固碳潜力为474.6—544.6 Gg C/a。根据未来气候变化情景和预测结果,到2030年、2050年、2100年,芦苇沼泽湿地的固碳潜力分别为576.9—655.1Gg C/a,603.3—684.1Gg C/a,680.9—769.4Gg C/a,其中由人工灌溉苇田的潜力最大。     

Plant community recovery after herbicide management to remove Phragmites australis in Great Lakes coastal wetlands

Invasive plants, such as Phragmites australis, are a global threat to plant diversity and are commonly controlled using herbicide management. The purpose of this study was to evaluate the plant community response 6–10 years after large‐scale herbicide management to remove Phragmites from Great Lakes coastal wetlands along the shores of western Lake Erie. Vegetation surveys were conducted in nine wetlands undergoing herbicide management and four unmanaged Phragmites‐dominated wetlands. The relative percent cover of Phragmites was dramatically lower in the managed (1.3%) compared to unmanaged wetlands (93.0%; p < 0.001), although relative percent cover of other non‐natives following herbicide management averaged 39.2% (ranging from 6.4 to 67.6%). The cover‐weighted floristic quality index was significantly higher in managed wetlands (p < 0.01), with the highest indices (12.4–17.0) at sites that received prescribed fire after herbicide treatment (p < 0.05). Species richness and diversity were significantly higher in managed wetlands (p < 0.001); however, there was no significant difference between wetlands treated only with herbicide and those treated with herbicide and prescribed fire. Our results indicate that herbicide management is effective in reducing Phragmites and improving floristic quality over timescales of 6–10 years. However, continued spot‐treatment and management of new invasive species may be required, and the return of high‐quality plant communities may be unrealistic in the study region.     

PhragNet: crowdsourcing to investigate ecology and management of invasive <Emphasis Type="Italic">Phragmites australis</Emphasis> (common reed) in North America

Invasion biology research, often performed by scientists at relatively small spatial scales, provides experimental precision but may be limited in generalizability. Conversely, large-scale invasive species management represents a largely untapped wealth of information on invasion ecology and management, but such data are difficult to capture and synthesize. We developed a network (“PhragNet”) of individuals managing wetlands occupied by native and non-native lineages of the invasive wetland grass Phragmites australis (common reed). This network collected environmental and genetic samples, habitat data, and management information to identify environmental and plant community associations of Phragmites invasion and patterns of management responses. Fifty managers overseeing 209 Phragmites stands in 16 US states and ON, Canada participated. Participants represented federal agencies (26%), municipalities (20%), NGOs (20%), academia (14%), state agencies (12%), and private landowners (8%). Relative to the native lineage, non-native Phragmites occurred in areas with higher nitrate/nitrite and ammonium than non-native Phragmites. Stand interiors had higher soil electrical conductivity than nearby uninvaded areas, consistent with use of road salt promoting spread of Phragmites. Non-native Phragmites co-occurred with fewer plant species than native Phragmites and was actively targeted for management. Herbicide was applied to 51% of non-native stands; surprisingly, 11% of native stands were also treated with herbicide. This project demonstrates the utility of crowdsourcing standardized data from resource managers. We conclude by describing how this approach could be expanded into an adaptive management framework, strengthening connections between wetland management and research.     

Species Composition and Inter-annual Dynamics of a Freshwater Tidal Plant Community Following Removal of the Invasive Grass, Phragmites australis

We document the regeneration of native freshwater wetland plant assemblages following removal of the common reed, Phragmites australis (Cav.) Trin. ex Steudel from two sites at Chapman Pond, East Haddam, Connecticut, USA. We gathered field data on composition of the vegetation 1 year before and for each of the 3 years after the removal in fall 1995/spring 1996 of Phragmites by two slightly different methods (hand-removal and herbiciding in one area, mowing/mulching and herbiciding in another). An area where Phragmites was left intact was similarly monitored. Our goals for this monitoring were: (1) to document plant species composition and richness before and after Phragmites removal and (2) to examine temporal and spatial variability in patterns of plant recruitment. Phragmites declined in both density and extent in both plots where removal treatments were applied. Richness, evenness, and density of non-Phragmites species increased steadily from 1996 to 1997 in all removal and intact plots. However, the species composition of the removal plots was richer than that of the intact plot, and more closely resembled that of comparable, uninvaded freshwater tidal wetlands. Rates of recovery of species richness in the removal plots declined from 1997 to 1998, potentially reflecting saturation of available colonization space, or the return of Phragmites. Phragmites has expanded its range in both of the removal plots since 1997. A model of its colonization indicates that Phragmites occupies space through localized proliferation of dense rhizomes rather than diffusely foraging with long tillers. Vigilance in monitoring is needed to document the spread of invasives, to evaluate the multi-faceted ecological effects of eradication efforts on both the invader and the regenerating community, and develop strategies for preventing re-invasion.     

A phylogeographic study of the cosmopolitan genus Phragmites (Poaceae) based on AFLPs

Within the genus Phragmites (Poaceae), the species P. australis (the common reed) is virtually cosmopolitan, and shows considerable variation in ploidy level and morphology. Genetic variation in Phragmites was studied using AFLPs, and analysed with parsimony and distance methods. Groups of P. australis strongly supported in the analyses include one that comprises all South American clones, a distinct group from the US Gulf Coast, and a group of E. Asian and Australian octoploids. Among the other species, the paleotropical P. vallatoria is supported as monophyletic and most closely related to the paraphyletic P. mauritianus and to the Gulf Coast and S. American groups. The E. Asian species P. japonicus is closely related to a group of P. australis clones mostly from central North America. Tetraploidy predominates in the genus, and optimisation of chromosome numbers onto the phylogeny shows that higher ploidy levels have evolved many times.     

Control of <Emphasis Type="Italic">Lepidium latifolium</Emphasis> (perennial pepperweed) and recovery of native plants in tidal marshes of the San Francisco Estuary

Several management techniques are effective in controlling Lepidium latifolium (perennial pepperweed) in rangelands and hay meadows; however, this invader’s rapid spread into sensitive aquatic habitats throughout the western US calls for alternative control strategies. To evaluate control methods for use in tidal marshes of San Francisco Estuary, we tested chemical, mechanical, and biological methods in field and greenhouse experiments. In a field experiment in three brackish marshes spanning the estuary, application of the herbicide glyphosate to re-growth of L. latifolium following hand-removal reduced L. latifolium cover by an average of 80% after 2 years and led to a 60% increase in native vegetation cover. Glyphosate alone was less effective at reducing L. latifolium cover (20% decrease) and increasing native cover (34% increase). Preliminary tests of a potential biological control, a native parasitic plant, were not successful, thus plots intended for field trials were instead used to test the newly approved herbicide imazapyr, which showed promise in controlling L. latifolium. An additional greenhouse experiment found large reductions in stem lengths with either glyphosate following clipping or imazapyr with or without clipping, all significantly more so than glyphosate alone. We conclude that an integrated management approach of applying glyphosate following mechanical removal can be effective at reducing L. latifolium cover and allowing recovery of native tidal marsh plants, providing a useful solution for controlling smaller, accessible infestations of the invader. Our preliminary tests of imazapyr suggest that it may be very effective at controlling L. latifolium in tidal marshes, although further assessment of non-target effects and native plant recovery are needed to evaluate its relative merit.     

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.     

The Effects of Phragmites Removal on Nutrient Pools in a Freshwater Tidal Marsh Ecosystem

Selected nitrogen and phosphorus pools in two freshwater tidal marsh ecosystems on the lower Connecticut River were measured relative to Phragmites, Typha and mixed native wetland plant cover types. For both the Chapman Pond Preserve and Chester Creek Marsh, significant differences were found between plant cover types in porewater ammonium and phosphate for some months during the 1998 growing season; porewater nitrate was always below the detection limit. At Chapman Pond, no significant differences were detected between Phragmites and Typha for plant tissue N concentrations. The standing stock of nitrogen was higher in Phragmites stands, however, owing to its greater aboveground biomass. No significant difference was found between plant cover types for total soil N at Chapman Pond, but KCl extractable ammonium was higher in the mixed cover type than Phragmites or Typha. The results of this study suggest that Phragmites is affecting nutrient pools in freshwater tidal marshes, a result that should be considered in future management design.     

Factors that influence vital rates of Seaside and Saltmarsh sparrows in coastal New Jersey,USA

As saltmarsh habitat continues to disappear, understanding the factors that influence the population dynamics of saltmarsh breeding birds is an important step in the conservation of these declining species. Using 5 yrs (2011–2015) of demographic data, we evaluated and compared apparent adult survival and nest survival of Seaside (Ammodramus maritimus) and Saltmarsh (A. caudacutus) sparrows at the Edwin B. Forsythe National Wildlife Refuge in New Jersey, USA. We determined the effect of site management history (unditched vs. ditched marshes) on adult and nest survival to aid in prioritizing future management or restoration actions. Apparent adult survival (61.6%, 95% CI: 52.5–70.0%) of Seaside Sparrows averaged > 1.5 times greater than that of Saltmarsh Sparrows (39.9%, 95% CI: 34.0–46.2%). Nest survival and predation and flooding rates did not differ between species, and predation was the primary cause of nest failure for both species. Apparent adult survival and nest survival did not differ between unditched and ditched marshes for either species, indicating that marsh ditching history may not affect the quality of breeding habitat for these species. Because predation was the primary cause of nest failure for both species in New Jersey, we suggest that future studies should focus on identifying predator communities in salt marshes and the potential for implementing predator‐control programs to limit population declines.     

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.     

Modeling the role of the close‐range effect and environmental variables in the occurrence and spread of Phragmites australis in four sites on the Finnish coast of the Gulf of Finland and the Archipelago Sea

Phragmites australis, a native helophyte in coastal areas of the Baltic Sea, has significantly spread on the Finnish coast in the last decades raising ecological questions and social interest and concern due to the important role it plays in the ecosystem dynamics of shallow coastal areas. Despite its important implications on the planning and management of the area, predictive modeling of Phragmites distribution is not well studied. We examined the prevalence and progression of Phragmites in four sites along the Southern Finnish coast in multiple time frames in relation to a number of predictors. We also analyzed patterns of neighborhood effect on the expansion and disappearance of Phragmites in a cellular data model. We developed boosted regression trees models to predict Phragmites occurrences and produce maps of habitat suitability. Various Phragmites spread figures were observed in different areas and time periods, with a minimum annual expansion rate of 1% and a maximum of 8%. The water depth, shore openness, and proximity to river mouths were found influential in Phragmites distribution. The neighborhood configuration partially explained the dynamics of Phragmites colonies. The boosted regression trees method was successfully used to interpolate and extrapolate Phragmites distributions in the study sites highlighting its potential for assessing habitat suitability for Phragmites along the Finnish coast. Our findings are useful for a number of applications. With variables easily available, delineation of areas susceptible for Phragmites colonization allows early management plans to be made. Given the influence of reed beds on the littoral species and ecosystem, these results can be useful for the ecological studies of coastal areas. We provide estimates of habitat suitability and quantification of Phragmites expansion in a form suitable for dynamic modeling, which would be useful for predicting future Phragmites distribution under different scenarios of land cover change and Phragmites spatial configuration.     

Microscale Spatial Distribution of Phragmites australis (Common Reed) Invasion into Spartina patens (Salt Hay)-dominated Communities in Brackish Tidal Marsh

Over the last century, Phragmites australis (common reed) has been expanding rapidly from the marsh–upland boundary into Spartina patens (salt hay)-dominated high marsh communities of the eastern US coast. Whereas direct and indirect human disturbances and changes in hydrology or salinity are likely to influence rates of spread at the landscape scale, the susceptibility of specific plant communities to invasion also influence rates of Phragmites expansion at the local scale. I measured microscale (0.25 m²) spatial patterns of culms (emerging buds and mature stems) in October 1993 at both expanding and stable boundaries of Phragmites populations within a S. patens-dominant matrix. In both expanding and stable plots, Phragmites culms were observed more frequently than expected on hummocks that were created by S. patens tussock-forming root structure. Culm density within a plot was correlated with the percent hummock cover within a plot. Further, Phragmites culms, particularly mature stems, were concentrated along the perimeter of the hummocks. Because the culms were not evenly distributed between hummocks and hollows, I suggest that invasion rates of Phragmites are limited in S. patens communities by microscale differences in hummock availability. The pattern of emergence suggests that expanding rhizomes of Phragmites encounter both competition with S. patens roots on the hummocks and physiological stressors (salinity, anoxia, sulfide concentrations) in the hollows.