Juncus Gerardi Research Articles

Micromorphology of the halophyte Juncus gerardii Loisel. subsp. gerardii (Juncaceae)

It has been established that anatomical structure of vegetative organs of the halophyte Juncus gerardii subsp. gerardii combines xeromorphic and halomophic features. Such features as parenchyma lining, good development of bulliform cells, and weak development of mechanical tissue are typically halomophic. However, plants also have features considered as xeromorphic: e.g. smaller cells of the tissues, the high length of the cells in palisade mesophyll (in the leaves), and length of the cells in chlorenchyma (in the stem). The seeds of J. gerardii subsp. gerardii have not special morphological or anatomical adaptations to germination at the high level of salinity.

Methane, carbon dioxide and nitrous oxide fluxes from a temperate salt marsh: Grazing management does not alter Global Warming Potential

Soil greenhouse gas emissions from cattle grazed and un-grazed temperate upper salt marsh were measured using dark static chambers, monthly for one year. Below-ground gas sampling tubes were also used to measure soil methane (CH4) concentrations. CH4 efflux from grazed and un-grazed salt marsh did not differ significantly although grazing did lead to ‘hotspots’ of underground CH4 (up to 6% of total air volume) and CH4 efflux (peak of 9 mg m−2 h−1) significantly linked to high soil moisture content, low soil temperatures and the presence of Juncus gerardii. Carbon dioxide (CO2) efflux was greater from the un-grazed marsh (mean of 420 mg m−2 h−1) than the grazed marsh (mean of 333 mg m−2 h−1) throughout most of the year and was positively correlated with the deeper water table and greater soil temperatures. Grazing was not a significant predictor of nitrous oxide (N2O) soil emissions. Global Warming Potential (GWP; over 100 years), calculated from mean yearly chamber fluxes for CH4 and CO2, did not differ significantly with grazing treatment. Seasonal variation in the key drivers of soil greenhouse gas efflux; soil temperature, moisture and water table, plus the presence or absence of aerenchymatous plants such as J. gerardii were more important to the magnitude of greenhouse gas emissions than grazing management per se.

Alien species of plants in aquatic and semiaquatic ecosystems of the Vyatka-Kama Cis-Urals

In the territory of the Vyatka-Kama Cis-Urals, 22 species of alien macrophytes are recorded. They compose 6.5% of the number of known macrophyte species known for the region. Most of them do not play an active role in formation of vegetative communities and constitute a part of aquatic communities as accompanying elements (Amaranthus retroflexus, Chenopodium glaucum, C. rubrum, Xanthium strumarium, Epilobium pseudorubescens, Juncus gerardii, Senecio vulgaris, Typha laxmannii, Mimulus guttatus, Butomus junceus, Scirpus tabernaemontani, and Zannichellia repens). They grow in secondary and open natural ecotones and do not pose a serious threat to aquatic ecosystems in the region because of their low activity in aquatic communities. Among alien species of macrophytes, invasive species are encountered. Some of them (Najas major, Vallisneria spiralis, Phragmites altissimus, Juncus tenuis, and Echinochloa crusgalli) have become a constant part of secondary biotope communities but pose a threat to indigenous macrophyte species only in specific biotopes where ecological conditions differ significantly from normal ones. Other species (Elodea canadensis, Epilobium adenocaulon, Impatiens glandulifera, Mentha longifolia, and Lemna gibba) have successfully naturalized in natural ecosystems or have been penetrating into them. The overwhelming majority of alien macrophyte species within the region are plants which do not refer to aquatic plants: hygrophytes (ten species or 45.5%) and hygromesophytes (three species or 13.6%). Only five species (22.7%) belong to hydrophytes and four species are helophytes (18.2%). Six species of alien macrophytes are characterized by transcontinental (North America) drift, 12 species (54.5%) are characterized by transzonal drift, and four species (18.2%) have been introduced from adjacent natural zones.

Ecological re-engineering of a freshwater impoundment for salt marsh restoration in a hypertidal system

The purpose of this paper was to examine the vegetative, sedimentary, nekton and hydrologic response to ecological re-engineering of a freshwater impoundment in the Upper Bay of Fundy. The dyke was breached in five locations and one channel initiated to connect the river to the borrow pit behind the dyke. This triggered significant self-organization within the restoration site. Existing channels (e.g. borrow pit) were incorporated within the newly excavated and developing creek system, increasing the hydraulic connectivity within the marsh and increasing fish habitat. Vegetation colonization, primarily by Spartina alterniflora, was rapid with almost 100% coverage by the end of the third year. Species associated with high marsh communities such as Juncus gerardii, Scirpus robustus, Ranunculus cymbalaria and Puccinellia maritima were present in increasing abundance post-restoration at the restoration site. The constructed channel eroded downward 2.3 m and the head of the channel retreated 35 m in response to the increased tidal prism. In the year immediately following the breach (2006), the surface of the marsh was unconsolidated and rates of change in surface elevation measured at RSET stations ranged from −0.7 (±0.1) to 1.7 (±0.2) cm yr −1 (±1SE). Measurements between years are highly variable. By year 3 the rate of surface elevation change decreased to a more moderate but variable mean of 0.3 (±0.6) cm yr −1 with the marker horizons recording mean accretion rates of 0.7 cm yr −1. This implies subsurface consolidation as the sediments dewatered or organic matter decomposed and vegetation became more established. Fish density decreased after restoration, however, remained higher than at the reference site for most years.

Litter legacy increases the competitive advantage of invasive Phragmites australis in New England wetlands

Exotic plant invaders that form monocultures and exclude native plants are often the most detrimental to native diversity and the hardest to eradicate. To generate a monoculture, the invader must garner more resources than resident natives and, once established, persist despite high densities of conspecific neighbors. Coincident with expansion and long-term persistence, successful invaders typically accumulate senesced material, but the role of this litter in mediating the invader’s ability to establish and maintain monospecific dominance has rarely been investigated. We used stands of the common reed, Phragmites australis, a prolific wetland invader in North America, to explore the impact of litter on interspecific competition with the native rush, Juncus gerardii, and intraspecific competition among live shoots. In 10 × 10 m areas positioned on Phragmites expansion fronts, we removed litter to isolate its effect from live Phragmites on light availability, aboveground biomass and community composition. Compared to adjacent, unmanipulated fronts, light availability nearly tripled and Juncus biomass increased >170% in litter removal areas after 4 months. Although the positive response of Juncus and native forbs was most pronounced on the leading edge of Phragmites stands, litter removal triggered a 271% increase in native plant biomass even in the interior of stands where Phragmites’ live stem density was highest. Litter treatment did not significantly affect Phragmites biomass, but more, shorter stems emerged in litter removals revealing Phragmites modifies stem phenotype in response to local litter and light conditions. These results suggest that litter plays a central role in Phragmites’ invasion process, from initial establishment to subsequent monospecific dominance. Thus, prescribed litter removal may be an effective strategy to enhance coexistence of native plant populations in wetlands where eradication of invasive monocultures is not an ecologically or economically feasible option.

Consequence of ramet defoliation on plant clonal propagation and biomass allocation: Example of five rhizomatous grassland species

We investigated the effects of ramet defoliation frequency on clonal propagation and the patterns of biomass production and allocation on five rhizomatous species ( Carex divisa Hude., Eleocharis palustris L., Juncus articulatus L., Juncus gerardii Lois. and Elytrigia repens L.). Plants were grown during an 18-week experiment in greenhouse conditions. The above ground parts of ramets were clipped following three treatments: frequent (every 2 weeks), moderate (every 4 weeks) and unclipped (control). The growth of C. divisa, J. articulatus and E. repens was strongly affected by defoliation whereas E. palustris and J. gerardii maintained a similar performance when defoliated. The latter were able to compensate for the biomass loss even after six consecutive clippings. Defoliation frequency had a significant effect on total biomass production for C. divisa, J. articulatus and E. repens while J. gerardii and E. palustris maintained total biomass production. Most of the studied species showed a decrease in clonal traits when defoliated. Clipped plants displayed fewer and shorter rhizomes. Defoliation had a strong influence in biomass production with a decrease in rhizome mass in all clipped species. A greater allocation to aerial parts and a lower to rhizomes were also detected. Moderate defoliation entailed intermediate response in 1/3 of detected significant effects of defoliation on plant traits. Finally, in the experimental conditions, E. palustris and J. gerardii were the most tolerant species to defoliation, while J. articulatus was intermediate and C. divisa and E. repens had the lowest tolerance.

Growth of tissue culture–regenerated salt marsh monocots in a simulated marsh field plot: Implication for wetland creation and restoration

Phenotypically and genetically variable salt marsh plants are needed for wetland creation and restoration efforts. Selected tissue culture regenerants of five salt marsh monocots, Spartina patens, Spartina alterniflora, Juncus gerardi, Juncus roemerianus, and Scirpus robustus, were planted in a simulated marsh field plot that was flood-irrigated with 10 ppt salt water to compare their phenotypic variation for potential use in wetland projects. Plant growth was evaluated after one growing season. Phenotypic variation among regenerants was found in S. alterniflora, S. patens and J. gerardi, indicating the occurrence of somaclonal variation. In S. alterniflora, significant differences occurred among regenerants in stem density. In J. gerardi, significant differences occurred in height and clone circumference. In S. patens, two of the nine regenerants exhibited higher biomass and stem density than some of the other regenerants. By using the random amplified polymorphic DNA (RAPD) technique, genome DNA variation in S. patens regenerants was detected. Genetic variation not only occurred among phenotypically different regenerants, but also among those phenotypically similar for the characteristics measured. Tissue culture–regenerated plants often have desirable genetic characteristics and adaptability as a result of somaclonal variation and may enable a species to perform its ecological functions in created or restored wetlands where ideal environments cannot be achieved. Thus, some previously unrestorable sites may be restorable or marginal marshes made more productive.

C3/C4 variations in salt-marsh sediments: An application of compound specific isotopic analysis of lipid biomarkers to late Holocene paleoenvironmental research

In salt-marshes, bulk carbon isotope values reflect organic matter contributions not only from salt-marsh plants, but also from algal and bacterial inputs, as well as allochthonous terrestrial organic matter. In the present study, compound specific isotope analysis was applied to a core and modern plant samples collected from a Machiasport, Maine salt-marsh. We sampled 10 plant species common to the marsh including Spartina alterniflora, Spartina patens, Juncus gerardi, Solidago sempervirens, Salicornia europa, Potentilla anserina, Atriplex patula, Plantago maritima, Suaeda maritima and Limonium nashii. Isolation of two n-alkanes (C 27 and C 29) present in marsh plant samples allowed for the reconstruction of past plant communities present in the cored deposits. For the C 27 and C 29 homologues there is a 3–10‰ separation in carbon isotopic composition between C3 and C4 species. Carbon isotopic values down core show a transition from a C4 dominated plant community to a C3 dominated community, attributable to the migration of lower marsh zones onto brackish/freshwater marsh zones during a late Holocene relative sea-level rise. The two homologues used have the potential to provide paleoenvironmental information in future core work, where the sea-level variable will be controlled.

Blocking Phragmites australis reinvasion of restored marshes using plants selected from wild populations and tissue culture

This study tested a vegetation strategy for controlling Phragmites australis invasion into brackish marshes as an alternative to the current technique of repeated herbicide sprays followed by burning. This strategy involves blocking P. australis by planting desired plants selected from wild populations and/or tissue culture regenerants at key points on the major routes of P. australis invasion. The planting of native species was conducted at three sites in a herbicide-treated P. australis marsh near Salem, NJ. Wild population selections of three upland marsh shrubs, Myrica cerifera, Baccharis halimifolia, and Iva frutescens, as well as two grass species, Spartina alterniflora and Spartina patens, and two rushes, Juncus gerardi and Juncus roemerianus, were planted according to their normal zonation positions. Tissue culture regenerated plants of the two grasses and two rushes, and the sedge species Scirpus robustus, were also planted. Plant growth at each site was monitored each year after planting for up to 3 years. Most plants of B. halimifolia, I. frutescens, J. roemerianus, and S. patens demonstrated a consistent vigorous growth at all three sites, whether or not the plants were collected from wild populations or were tissue culture regenerants. These multi-layered walls of plants demonstrated effectiveness in controlling the P. australis by restricting or inhibiting its spread. Upon screening 48 regenerated plants of S. patens at one of the three sites, we found that some regenerants showed enhanced characteristics for blocking P. australis, such as greater expansion and a high stem density. The availability of the tissue culture-regenerated plants of the native marsh species makes it possible to select lines from local genotypes that have desirable characteristics for wetland restoration projects, such as blocking P. australis reinvasion.

Mechanisms of exclusion of native coastal marsh plants by an invasive grass

Summary 1 Determining the mechanisms by which invasive species exclude natives is critical for conserving and restoring native populations in impacted habitats. In recent decades the grass Phragmites australis has been aggressively invading coastal marshes of North America, with monocultures often replacing diverse assemblages of plants. 2 Our objective was to quantify how P. australis modifies the abiotic (soil and light conditions) and biotic (litter and shoots) environment and to determine the mechanisms by which it excludes two common forbs, the annual chenopod Atriplex patula var. hastata and the perennial aster Solidago sempervirens, from the highest tidal elevations of a brackish marsh in southern New England, USA. 3 In a 3-year field experiment we added seeds of both forb species to stands of P. australis, where we manipulated shoots and litter in an orthogonal design, and to uninvaded marsh areas dominated by the rush Juncus gerardi, where we manipulated the shoots of the marsh vegetation. In general, seedling establishment and the number of plants surviving until the end of the growing season were substantially greater in areas not invaded by P. australis, and both shoots and litter limited the abundance of forbs within stands. 4 Forbs surviving within stands of P. australis grew larger and produced more seeds than those in uninvaded areas, indicating that changes to the soil resulting from invasion do not preclude the survival of established forbs. This was confirmed by a glasshouse study where the performance of forbs in soil collected from within stands of P. australis was better than in soil from areas dominated by J. gerardi. 5 Similar to many invasive grasses in terrestrial communities, P. australis excludes native forbs through competition, modifying the biotic environment of the marsh at both the ground (litter) and above-ground (shoots) levels. Our results suggest that successful invaders, such as P. australis, are likely to be the ones that can engineer habitats in multiple ways and limit populations of native species across several critical stages of their life history.

Tissue culture and plant regeneration of the salt marsh monocots Juncus roemerianus and Juncus gerardi

Tissue culture and plant regeneration protocols for the salt marsh plants Juncus roemerianus Scheele and Juncus gerardi Loisel, were developed. J. roemerianus callus was induced from mature seeds cultured on Murashige and Skoog (MS) medium supplemented with 2.22 μM 6-benzylaminopurine (BA), 5.37 μM α-naphthaleneacetic acid (NAA), 2.26 μM 2,4-dichlorophenoxyacetic acid (2,4-D), and 50 ml l−1 coconut water (callus induction medium). The callus was subcultured on MS medium containing 2.22 μM BA, 5.37 μM NAA, and 9.05 μM 2,4-D for callus maintenance. Shoot regeneration occurred 2 wk after transferring the callus onto shoot regeneration medium, which consisted of MS medium containing BA or thidiazuron. A high frequency of shoot regeneration was obtained when the medium contained 13.3 μM BA. Regenerated shoots were transferred to MS medium supplemented with 10.7 μM NAA for root production. Rooting did not occur in the shoots regenerated on the thidiazuron-containing media. The callus induction medium for J. roemerianus was also effective in inducing callus of J. gerardi from young inflorescences. The same medium was also used for callus maintenance. Shoot regeneration occurred 10 d after transferring the callus onto MS medium supplemented with 0.44 μM BA and 0.57 μM indole-3-acetic acid. Root regeneration occurred after transferring the shoots onto MS medium plus 0.44 μM BA and 14.8 μM indole-3-butyric acid. The regenerated plants of both J. roemerianus and J. gerardi grew vigorously in potting soil in the greenhouse. J. roemerianus regenerants also grew well in a saltwater-irrigated field plot. Tissue culture-produced plants of J. roemerianus and J. gerardi can be used for planting in created or restored wetlands.

Salinity tolerance during germination of seashore halophytes and salt-tolerant grass cultivars

Direct sowing is the simplest method of plant establishment for restoration and remediation purposes, but relatively few plants can establish under high salinity conditions. In this study, the ability of different seashore plants and grass cultivars to germinate in different dilutions of seawater (0–400 mM NaCl) was tested. Highest germination was found in distilled water or seawater dilutions up to 100 mM NaCl. When seawater concentrations were increased from 100 to 200 mM NaCl, a strong decline in germination percentage and rate was observed in less salt-tolerant species, such as Matricaria maritima and Achillea millefolium. The more salt-tolerant species, Plantago maritima, Juncus gerardii, Artemisia vulgaris, Agrostis spp. and Rumex spp., had a threshold salinity, where germination was significantly decreased in seawater dilutions between 200 and 400 mM NaCl. Even among the salt-tolerant species, only two, Agrostis stolonifera and Artemisia vulgaris, germinated at 400 mM. Variation in salinity response was observed among populations of Artemisia vulgaris and among cultivars of Festuca spp. Increasing salinity to 200 mM NaCl delayed germination in most species. Ungerminated seeds of most salinity-tolerant species were still viable after 21 d at the highest salinity (400 mM), and showed a rapid and high germination when transferred to distilled water. These species would be able to survive high salinity and germinate when the salinity of the sediments decreases through dilution or leaching of salts. The experiment revealed species and cultivars that will be of interest in further testing for restoration and remediation in saline habitats.

Effects of stressors on invasive and halophytic plants of New England salt marshes: A framework for predicting response to tidal restoration

Salt marsh restoration practices based on the reintroduction of tides to hydrologically-altered wetlands may be hindered by a lack of specific knowledge regarding plant community response to environmental change. Since saltmarsh plant communities are controlled by physical stress tolerance and competition, we conducted a field experiment that measured effects of saltwater flooding and competitive interactions on plants as a guide for predicting habitat response to tidal restoration. Six plant species of New England salt marshes were studied: halophytes Spartina alterniflora, Spartina patens, and Juncus gerardii and brackish invasive species Phragmites australis, Typha angustifolia, and Lythrum salicaria. Plant shoots were transplanted across a gradient of three flooding and three salinity regimes and arranged into pair-wise competitive combinations. After one growing season, saltwater flooding was found to decrease transplant survival, biomass production, and/or relative growth for all species. Reduction in halophyte growth was largely due to increased flood duration; brackish species were most reduced by increased salinity. Interspecific competition also influenced species growth, although the short duration of the study may have weakened these effects. Transplants paired with S. alterniflora had reduced growth, but combinations with Juncus produced increased growth. Standardized factors of stress tolerance and relative competitive strength were derived for the six study species as a framework for understanding community-level changes in marshes. As an aid to resource managers, experimental results can be used to predict plant community response to existing and potential alterations in saltmarsh tidal hydrology.

Determinants of expansion forPhragmites australis, common reed, in natural and impacted coastal marshes

The rapid spread ofPhragmites australis in the coastal marshes of the Northeastern United States has been dramatic and noteworthy in that this native species appears to have gained competitive advantage across a broad range of habitats, from tidal salt marshes to freshwater wetlands. Concomitant with the spread has been a variety of human activities associated with coastal development as well as the displacement of nativeP. australis with aggressive European genotypes. This paper reviews the impacts caused by pure stands ofP. australis on the structure and functions of tidal marshes. To assess the determinants ofP. australis expansion, the physiological tolerance and competitive abilities of this species were examined using a field experiment.P. australis was planted in open tubes paired withSpartina alterniflora, Spartina patens, Juncus gerardii, Lythrum salicaria, andTypha angustifolia in low, medium, and high elevations at mesohaline (14‰), intermediate (18‰), and salt (23‰) marsh locations. Assessment of the physiological tolerance ofP. australis to conditions in tidal brackish and salt marshes indicated this plant is well suited to colonize creek banks as well as upper marsh edges. The competitive ability ofP. australis indicated it was a robust competitor relative to typical salt marsh plants. These results were not surprising since they agreed with field observations by other researchers and fit within current competition models throught to structure plant distribution within tidal marshes. Aspects ofP. australis expansion indicate superior competitive abilities based on attributes that fall outside the typical salt marsh or plant competition models. The alignment of some attributes with human impacts to coastal marshes provides a partial explanation of how this plant competes so well. To curb the spread of this invasive genotype, careful attention needs to be paid to human activities that affect certain marsh functions. Current infestations in tidal marshes should serve as a sentinel to indicate where human actions are likely promoting the invasion (e.g., through hydrologic impacts) and improved management is needed to sustain native plant assemblages (e.g., prohibit filling along margins).

Microclimate and substrate quality controls on nitrogen mineralization in a New England high salt marsh

New England high salt marsh primary productivity is limited by N, but variation in plant N availability across salt marsh vegetation zones has not been quantified. To investigate this, we measured in situ net N mineralization rates throughout the growing season in three zones of a Maine high salt marsh, Juncus gerardii, Spartina patens, and mixed perennial forb. We also measured microclimate factors (soil temperatures and moistures) and sub strate quality parameters (soil organic matter, soil total nitrogen, soil C:N ratio) to see if either related to differ ences in net N mineralization. To determine the relative importance of substrate quality and microclimate, we measured N mineralization of the different soil types in the laboratory, holding microclimate parameters con stant. We also investigated the relative importance of microclimate and substrate statistically, with principal com ponents analysis and multiple regression. In situ net N mineralization rates were significantly higher in the forb zone than in graminoid zones, but graminoid zone N mineralization rates did not vary significantly from each other. Soil temperatures, moistures, carbon, and nitrogen were all significantly higher in the forb zone than in graminoid zones, but C:N ratio did not vary significantly across zones. Principal components analysis and mul tiple regression revealed that microclimate was a more significant predictor of total N mineralized over the course of the growing season than was substrate quality. In contrast, when microclimate conditions were held constant, forb zone N mineralization was still significantly higher than that of graminoid zones, suggesting that substrate quality does exert some control on this process. Thus, both microclimate and substrate quality appear to influ ence N mineralization rates across vegetation zones of this Maine salt marsh.

Effects of haying on salt-marsh surface invertebrates.

Marsh plants may affect the structure of epibenthic communities in a variety of ways. They might reduce temperature stress on organisms by shading, provide refuge from predators, increase the rate of organic matter accumulation at the sediment surface, and serve as a food source. Thus, salt marsh plants might control the spatial distributions of epibenthic invertebrates within the marsh. An ongoing “experiment” on the impact of the periodic removal of plants has been carried out by New England farmers who have been haying some salt marshes for over 300 years. Earlier research by the Plum Island Estuary Long-Term Ecological Research project (PIE-LTER) has shown that haying causes a short-term increase in the growth of benthic algae (1), causes a shift in the diet of some marsh invertebrates to a greater percentage of algae (2), and results in a change in plant species composition (PIE-LTER, unpubl. results). To determine the shortand long-term effects of haying on the epibenthic community and to identify the principal variables controlling the distribution of epibenthic invertebrates, we carried out two sets of experiments: a marsh-grass-removal experiment to mimic the effects of haying and a survey of invertebrates in areas of the marsh subjected to different haying schedules. Our work was conducted in the Plum Island Sound estuary in Rowley, Massachusetts, from June to August 2002. For our marsh-grass-removal experiment, we clipped and removed the vegetation from three randomly selected circular sites of 3-m radius along a 50-m transect in a marsh that is hayed roughly every other year. Before clipping we counted organisms in four 0.25-m sampling areas, located 1.5 m from the center of the circle and equidistant from each other, within each of the three sites. We sampled the same four areas within each site immediately before clipping, and 1 and 4 days after clipping. Differences in abundances of organisms before and after clipping were evaluated by the Kruskal-Wallis test with time of sampling as treatment. Because differences among circular hayed sites were not significantly different, we pooled replicates from each site before our analysis. For our surveys of invertebrates in areas subjected to different intensities of haying, we examined randomly selected sites in recently hayed and reference marshes along 12 previously established transects for which GPS elevation data were available. We sampled 40 sites between 1 and 3 July, and 40 more between 16 and 18 July. At each site, we visually estimated percent cover of different plant species. A count of organisms was made after clipping all vegetation from 0.25-m plots. A 177-cm plant sample was collected, live biomass was separated from standing dead biomass and weighed separately to determine above-ground biomass. Commonly encountered plants included Spartina patens, Spartina alterniflora, Distichlis spicata, Salicornia europaea, and Juncus gerardi. To evaluate the effect of plant cover on predation rate, we tethered amphipods, Orchestia grillus, to thin-diameter line and deployed 5 per site at most sites for 24 h before clipping. We used stepwise multiple regression to describe the relationship between measured environmental variables and abundance of epifauna for the 16–18 July sampling period (criteria P 0.1 to accept, P 0.25 to reject). Environmental variables used in stepwise multiple regression were haying frequency, elevation, temperature, humidity, dried live plant biomass, dried standing dead, total dried weight, percent live, percent dead, percent bare, percent S. alterniflora, percent S. patens, percent D. spicata, percent S. europaea, percent Atriplex patula, percent Triglochin maritima, percent Iva frutescens, proportion tethered live amphipods, and proportion eaten tethered amphipods. Collinearity among environmental variables was assessed by examining the variance inflation factor for each included variable. All variance inflation factors were less than 2, which indicated that collinearity among independent variables did not significantly affect our results. A few sampling sites were omitted from the regression analysis due to missing data. Analyses were performed using SPSS software.

Bacterioplankton community composition in flowing waters of the Ipswich River watershed.

moptera), and the isopod Philoscia vittata were the most common invertebrates encountered in the marsh. In the marsh-grass-removal experiment we found a significant decrease in abundance of leafhoppers ( [2] 26.9, P 0.0001), as well as spiders (Order Araneae) ( [2] 8.72, P 0.013), greenhead fly larvae (Tabanus nigrovittatus) ( [2] 14.23, P 0.001), and O. grillus ( 2 [2] 26.9, P 0.0001) after clipping (Fig. 1). P. vittata was not significantly affected ( [2] 3.32, P 0.19, Fig. 1). The stepwise multiple regression indicated that percent S. alterniflora, percent bare space, percent Salicornia europaea, and temperature were correlated with patterns of leafhopper abundance (F[4,32] 40.02, P 0.0001). The positive correlation between leafhoppers and S. alterniflora cover is consistent since leafhoppers often feed on S. alterniflora (3). Spiders were positively related to dead above-ground biomass, and percent bare space (F[2,34] 8.25, P 0.001), which is consistent with their reduced abundance in our experimental marsh-grass-removal treatments. The measured environmental variables related to the abundance of T. nigrovittatus larvae were percent Juncus gerardi, sediment surface temperature, and proportion of tethered amphipods eaten (F[3,33] 8.04, P 0.0001). The abundance of T. nigrovittatus larvae was negatively correlated with sediment surface temperature. It is likely that temperatures in the newly clipped patches were higher than in the unclipped marsh. Abundances of T. nigrovittatus larvae were also positively correlated with the proportion of tethered amphipods eaten, which is consistent with our observations of predation by T. nigrovittatus larvae on tethered O. grillus specimens. O. grillus abundance was not significantly correlated with any variables, and the amphipod was widely distributed throughout the marsh. The lack of a significant correlation with aboveground biomass or haying frequency is noteworthy since the amphipods experienced a strong drop in abundance in the marsh-grass haying experiment. This finding suggests that the long-term effects of haying on O. grillus abundances are much less severe than the immediate response. Many invertebrate species may experience a strong reduction in abundance just after haying; however, many environmental variables in addition to haying had an effect on patterns of invertebrate abundance in the long-term. We thank Carl Noblitt, our research assistant. This research was supported by an REU fellowship through the Plum Island Sound LTER program to JPL.

Soil seed bank and driftline composition along a successional gradient on a temperate salt marsh

Abstract. This study focuses on the relationship between vegetation succession and soil seed bank composition on the Schiermonnikoog (The Netherlands) salt marsh over 100 yr. The importance of driftline material in seed dispersal and the relationship with succession is also investigated. The results indicate that the majority of species have a transient or short‐term seed persistent bank. Seeds of most species are able to float over the salt marsh and become concentrated in the driftline higher up the marsh. After plants have established a seed bank forms, which disappears when vegetation is replaced by later‐successional species. Exceptions are Spergularia mar‐itima, which is still present in the seed bank of late successional stages, and Juncus gerardi and Glaux maritima, which appear in the seed bank of early successional stages, but are absent in the vegetation. Based on the results of this study constraints and possibilities for salt‐marsh restoration by de‐embankment are discussed.

Long‐term vegetation changes in experimentally grazed and ungrazed back‐barrier marshes in the Wadden Sea

Abstract. Vegetation succession in three back‐barrier salt marshes in the Wadden Sea was studied using a data set comprising 25 years of vegetation development recorded at permanent quadrats. The effect of livestock grazing on succession was assessed by comparing quadrats where grazing was experimentally prevented or imposed. We studied changes at the species level as well as at the level of the plant community. Special attention is given to effects on plant species richness and community characteristics that are relevant for lagomorphs (hares and rabbits) and geese. Inundation frequency and grazing were most important in explaining the variation in species abundance data. The three marshes studied overlap in the occurrence of different plant communities and the observed patterns were consistent between them. Clear differences in frequency and abundance of plant species were observed related to grazing. Most plant species had a greater incidence in grazed treatments. Species richness increased with elevation, and was 1.5 to 2 × higher in the grazed salt marsh. Grazing negatively influenced Atriplex portulacoides and Elymus athericus, whereas Puccinellia maritima and Festuca rubra showed a positive response. The communities dominated by Elymus athericus, Artemisia maritima and Atriplex portulacoides were restricted to the ungrazed marsh. Communities dominated by Puccinellia maritima, Juncus gerardi and Festuca rubra predominantly occurred at grazed sites. As small vertebrate herbivores prefer these plants and communities for foraging, livestock grazing thus facilitates for them.

Soil seed bank and driftline composition along a successional gradient on a temperate salt marsh

Abstract This study focuses on the relationship between vegetation succession and soil seed bank composition on the Schiermonnikoog (The Netherlands) salt marsh over 100 yr. The importance of driftline material in seed dispersal and the relationship with succession is also investigated. The results indicate that the majority of species have a transient or short-term seed persistent bank. Seeds of most species are able to float over the salt marsh and become concentrated in the driftline higher up the marsh. After plants have established a seed bank forms, which disappears when vegetation is replaced by later‐successional species. Exceptions are Spergularia maritima which is still present in the seed bank of late successional stages, and Juncus gerardi and Glaux maritima which appear in the seed bank of early successional stages, but are absent in the vegetation. Based on the results of this study constraints and possibilities for salt‐marsh restoration by de‐embankment are discussed. Nomenclature:van der ...