Halimione Portulacoides Research Articles

Halophyte vegetation influences in salt marsh retention capacity for heavy metals

We analysed concentrations of Cu, Cd and Pb in above and belowground tissues of the halophyte species Halimione portulacoides and Spartina maritima, as well as in sediments and pore water between the roots in a Tagus estuary salt marsh (Portugal). From these results we calculated the pools of metals in the compartments mentioned above. Relative percentages of accumulation in each pool were also determined. Our aim was to determine how the type of vegetation in the salt marsh affects overall metal retention capacity of the system. It was concluded that areas colonised by H. portulacoides are potential sources of Cu, Cd and Pb to the marsh ecosystem, whereas areas colonised by S. maritima are more effective sinks at least for Cu and Cd. Consequently, S. maritima seems to contribute more effectively to the stabilisation of metals in salt marsh sediments, reducing their availability to the estuarine system.

Validation and application of an analytical method for monomethylmercury quantification in aquatic plant tissues

An analytical methodology for monomethylmercury (MMHg) determination in aquatic plant tissues with low detection limit (346 pg g −1) is proposed. It consists of acid digestion (HBr/CuSO 4), cleanup step with a Na 2S solution, pre-concentration procedure using a dithizone solution in toluene and quantification by GC–ECD. The performance of the methodology has been tested by determining the MMHg concentrations in the certified reference material Fucus Sea Plant Homogenate—IAEA-140/TM (CRM) and in leaves, stems and roots of the salt marsh plants Sarcocornia fruticosa and Halimione portulacoides. The results obtained for CRM were not statistically different ( α = 0.056) from the certified value and repeatability was lower than 2.5% for the plant samples analyzed. This coefficient of variation was similar to those obtained in the externally quality control using within-batch and between-batch (<1.4%).

Terrestrial growth and marine dispersal? Comparative phylogeography of five coastal plant species at a European scale

AbstractThe phylogeography of five flowering plant species (Cakile maritima, Eryngium maritimum, Salsola kali, Halimione portulacoides, Crithmum maritimum) widespread along the European coasts was investigated across their entire European range using AFLP evidence. Both similarities and dissimilarities were found. All species contain a distinct Black Sea/Aegean Sea cluster, and all except E. maritimum contain a distinct Adriatic Sea cluster or group of genetically very similar clusters. All species except Cr. maritimum contain a distinct Atlantic Ocean/North Sea/Baltic Sea cluster clearly separate from the Mediterranean material. In Ca. maritima a distinct Baltic Sea subcluster was found. In the western Mediterranean, two species groups can be recognized. Whereas in S. kali and E. maritimum material from this area falls into only one cluster or a group of genetically very similar clusters, it falls into two clusters or groups of clusters of either more Atlantic or more central Mediterranean similarity in Ca. maritima, H. portulacoides and Cr. maritimum. Similarities and dissimilarities in patterns found are discussed in terms of a combination of historical and extant abiotic and biotic factors. Thus, the distribution range of all species in the eastern Mediterranean area was not affected by Quaternary temperature changes, resulting in phylogeographic congruency here. The existence of distinct Black Sea/Aegean Sea and Adriatic Sea clusters or groups of clusters is the result of sea currents isolating these regions from each other. In the western Mediterranean basin the more cold‐sensitive species (H. portulacoides, Cr. maritimum) but not the less cold‐sensitive species (S. kali, E. maritimum) had to retreat from northern coasts. Re‐colonization of these areas from two different directions is implied by their phylogeographic pattern. The existence of a distinct Gibraltar gap is explained in terms of extant sea currents. Comparison of phylogeographic patterns found with those observed in either marine or terrestrial organisms leads to the conclusion that marine dispersal is of overriding importance in these coastal plants.

Does the invasive plant Elymus athericus modify fish diet in tidal salt marshes?

The invasion of Mont-Saint-Michel Bay salt marshes (France) by a grass species ( Elymus athericus) has led to important changes in vegetation cover, which is likely to modify the habitat for many invertebrates. Some of them constitute the main food items for several fish species, such as young sea bass ( Dicentrarchus labrax) and sand goby ( Pomatoschistus minutus), that feed in salt marsh creeks during high tides. As a result, fish nursery functions of salt marshes could be modified by the E. athericus invasion. In order to test this hypothesis, gut contents of the two most abundant fish species (sea bass and sand goby) were compared before and after E. athericus invasion in the same salt marsh creek and using the same methodology. The accessibility and availability of the main food item, the semi-terrestrial amphipod Orchestia gammarella, were estimated and compared between invaded (dominated by E. athericus) and original areas (dominated by Atriplex portulacoides). Gut content analysis showed a significantly greater percentage of fish leaving with empty guts from E. athericus areas than from A. portulacoides areas. The sea bass diet composition study showed a major shift in the relative importance of the main food items: before E. athericus invasion, diets were dominated by the semi-terrestrial species O. gammarella, whereas after the E. athericus invasion they were dominated by a marine mysid Neomysis integer. The same trend was found for sand gobies, with a shift of the main food item from O. gammarella before invasion to the polychaete Hediste diversicolor after invasion. These trophic changes may be explained by the lower accessibility and availability of O. gammarella in invaded communities than in natural ones. The E. athericus invasion, observed throughout northern Europe, is thus likely to disturb trophic function of natural salt marshes for fish. This preliminary study of the E. athericus invasion is also an illustration that invasive species are an urgent problem in conservation biology.

Activity and growth efficiency of heterotrophic bacteria in a salt marsh (Ria de Aveiro, Portugal)

Bacterial utilization of monomers is recognized as an important step in the biogeochemical cycling of organic matter. In this study we have compared the heterotrophic activity of bacterial communities from different micro-habitats within a salt marsh environment (Ria de Aveiro, Portugal) in order to establish spatial patterns of bacterial abundance, monomer turnover rates (Tr) and bacterial growth efficiency (BGE). Differences in bacterial abundance and activity could be found between distinct plant rhizospheres. BGE tended to be lower at Halimione portulacoides banks, when compared to Sarcocornia perennis subsp. perennis banks which, on the contrary, showed the highest bacterial densities. Experiments of amendment of natural samples with organic and inorganic supplements indicated that salt marsh bacteria are not strongly regulated by salinity but the increased availability of labile organic matter causes a significant metabolic shift towards mineralization.

Plant type mediates rhizospheric microbial activities and soil aggregation in a semiarid Mediterranean salt marsh

This study was carried out in a Mediterranean salt marsh from semiarid Southeastern Spain, to determine the influence of eight halophytes ( Asteriscus maritimus (L.) Less., Arthrocnemum macrostachyum (Moric.) Moris, Frankenia corymbosa Desf., Halimione portulacoides (L.) Aellen, Limonium cossonianum O. Kuntze, Limonium caesium (Girard) O. Kuntze, Lygeum spartum L., and Suaeda vera Forsskål ex J.F. Gmelin growing in a homogeneous area with regard to salt content, on the rhizosphere soil microbiological and biochemical properties (labile C fractions, biomass C, oxidoreductases and hydrolases) and aggregate stabilisation. Rhizosphere soil of H. portulacoides showed the highest values of water-soluble C, water-soluble carbohydrates, microbial biomass C and dehydrogenase, urease, protease-BAA and acid phosphatase activities. S. vera had the lowest microbial activity. The soil under A. maritimus, L. cossonianum, L. spartum and H. portulacoides had the highest percentages of stable aggregates (on average, about 52%) and the soil under S. vera the lowest (about 27% of stable aggregates). There was a good correlation between enzyme activities, the C-biomass, root colonisation of the eight halophytes and the levels of stable aggregates. Our results suggest that soil microbial activity and soil properties related to microbial activity, such as aggregate stability, are determined by the type of the halophytic species.

Spectroscopic properties of sedimentary humic acids from a salt marsh (Ria de Aveiro, Portugal): comparison of sediments colonized by Halimione portulacoides (L.) Aellen and non-vegetated sediments

The influence of the colonization of salt marsh sediments with Halimione portulacoides, on the composition of the sedimentary humic acids was evaluated. For this purpose, cores of colonized and non-colonized sediments from a salt marsh in Ria de Aveiro (Portugal) were collected, and the humic acids of different layers were extracted and characterized by Fourier transform infrared, synchronous molecular fluorescence (Δλ = 60 nm) and UV-visible spectroscopies and also by elemental analysis. The infrared spectra suggest the presence of more peptide residues and carbohydrates in the sedimentary humic acids from surface and around the plant roots at the site colonized by H. portulacoides, when compared with the humic acids from the depth-equivalent sediment layers at the non-colonized site. The higher content of protein-type materials is confirmed by the lowest values of C/N ratios and the highest relative intensities of a band at λexc = 280 nm in the fluorescence spectra. The lowest e280 values obtained in the UV-visible spectra, and the infrared spectra suggest a lower aromatic content of the humic acids from the colonized site.

Temporal changes and spatial variation of soil oxygen consumption, nitrification and denitrification rates in a tidal salt marsh of the Lagoon of Venice, Italy

The aim of the present study was to investigate seasonal and spatial patterns of soil oxygen consumption, nitrification, denitrification and fluxes of dissolved inorganic nitrogen (DIN) in a tidal salt marsh of the Lagoon of Venice, Italy. In the salt marsh, intact soil cores including overlying water were collected monthly at high tide from April to October in salt marsh creeks and in areas covered by the dominant vegetation, Limonium serotinum. In May, cores were also collected in areas with vegetation dominated by Juncus maritimus and Halimione portulacoides. In laboratory incubations at in situ temperature in the dark, flux rates of oxygen and DIN were monitored in the overlying water of the intact cores. 15N-nitrate was added to the overlying water and nitrification and denitrification were measured using isotope-dilution and -pairing techniques. The results show that highest soil oxygen consumption coincided with the highest water temperature in June and July. The highest denitrification rates were recorded in spring and autumn coinciding with the highest nitrate concentrations. Soil oxygen consumption and nitrification rates differed between sampling sites, but denitrification rates were similar among the different vegetation types. The highest rates were recorded in areas covered with L. serotinum. Burrowing soil macrofauna enhanced oxygen consumption, nitrification and denitrification in April and May. The data presented in this study indicate high temporal as well as spatial variations in the flux of oxygen and DIN, and nitrogen transformations in the tidal salt marshes of the Venice lagoon during the growth season. The results identify the salt marshes of the Venice lagoon as being metabolically very active ecosystems with a high capacity to process nitrogen.

Long-chain (C19–C29) 1-chloro-n-alkanes in leaf waxes of halophytes of the Chenopodiaceae

The hydrocarbon fraction of leaf waxes of three halophytes of the Chenopodiaceae common to Mediterranean salt marshes (Suaeda vera, Sarcocornia fruticosa and Halimione portulacoides) revealed the presence of a minor series of odd and even chains 1-chloro-n-alkanes ranging from C19 to C29. The identification of these new chlorinated plant constituents was based on a combination of mass spectrometry data with selective chlorine detection (CPG-AED) and was confirmed by comparison with authentic standards. The qualitative and quantitative distributions of these 1-chloro-n-alkanes varied inter-specifically. Homologues with an odd carbon-chain were predominant in all species but maximised at C25 and C27 in S. vera and S. fruticosa, and at C27 and C29 in H. portulacoides. Remarkably, 1-chloro-nonacosane was an abundant homologue only in this latter species. Leaves of S. vera contained 4 to 7 times more of total chloroalkanes than leaves of the other two species. These compounds accounted for 10, 4 and 1% of the hydrocarbon fraction of leaf waxes of S. vera, S. fruticosa and H. portulacoides, respectively. Attempts to link the occurrence of these chloroalkanes with other classes of leaf waxes (n-alkenes, n-aldehydes and n-alcohols) did not allowed a clear precursor–product relationship to be established. The biological functions as well as the mode of synthesis of alkylchlorides in (halophyte) plants remain unknown but undoubtedly deserve further attention.

Heavy Metal Pollution and Biomonitoring Plants in Lake Manzala, Egypt

In this study, the pollution levels and the toxicity status were estimated regarding four heavy metals (Zn, Pb, Cd and Hg) thought to be among the major contaminants in the environment of Lake Manzala. Our target was to define and utilize certain plant species, from the lakeþs vegetation, as bio-monitors, in comparison with the sediments as abiotic monitor for heavy metal pollution. The native wild plants (passive bio- monitors) were represented by eight species (Atriplex portulacoides, Zygophyllum album, Typha domingensis Juncus rigidus, Cyperus laevigatus, Arthrocnemum macrostachyum, Salsola sp. and Phragmites australis). The introduced plants (active bio-monitors) were represented by two crop- species (Trifolium alexandrinum and Raphanus sativa) grown and irrigated by polluted water at some islands in the southern sector of LM. Based on the concentration and toxicity status, induced in the lake's vegetation and sediments, the four metals are arranged in the following decreasing order: Hg greater than Zn greater than Pb greater than Cd. Compared with the standard normal and critical toxicity ranges in plants and soils, the detected values of Zn, Pb and Cd were within the critical ranges. However, Hg showed the highest values and alarming toxicity levels and it is considered as one of the most hazardous pollutants in Lake Manzala. The overall evaluation of the tested metals showed that their ratios were as much as 2.5 - 5 times higher in active monitors than in passive ones and 2 times than in sediments. They were also 2 times higher in sediments than in passive monitors. The monitoring materials are arranged in a decreasing order, based on their efficiency for accumulating heavy metals as follows: Introduced (active) monitors greater than Sediments greater than Native (passive) monitors. Certain species are also proposed as bio-monitors (and/or bio-filters) for the studied heavy metal pollutants. The results showed that there is a significant difference between the accumulation rate of some metals in different plant organs (e.g. Zn, Hg) since they showed more tendency for accumulation in root more than shoot systems. Also, there is a high positive correlation between combinations of different metal pairs in either plantþs root or shoot system. It is evident that while the degree of metal pollution in the lake increased southwards, the values of water-quality parameters (e.g. dissolved oxygen %, salinity and pH-value) increased northwards.

Vegetation dynamics and plant species interactions under grazed and ungrazed conditions in a western European salt marsh

Abstract Experiments in exclosures were conducted on a salt marsh in a macrotidal system in western France. The aim of this study was threefold: (1) to compare vegetation dynamics over a period of 8 years in grazed and ungrazed conditions (2) to investigate the response of annual species to grazing duration during seedling establishment (3) to test the effect of an increase in soil nitrogen availability after cessation of grazing on interactions between Suaeda maritima and Puccinellia maritima . In grazed conditions, during all the survey, vegetation was dominated by a short P. maritima sward with the annual Salicornia europaea in the lower and middle marshes. However, after cessation of grazing in 1994, a homogeneous matrix of the forb Halimione portulacoides , quickly replaced P. maritima in the well drained lower marsh. At the middle marsh level, fine sediment and poor drainage maintained P. maritima while the annual S. maritima which tolerates taller and denser vegetation replaced S. europaea. Elymus pungens cover was limited till 2000 but its rising in 2001 let expect its dominance in the future. While P. maritima abundance remained high, spring abundance of annual species such as S. europaea and S. maritima globally decreased with sheep grazing duration on the salt marsh between February and June. Experiments with monocultures of P. maritima and S. maritima demonstrated that nitrogen was a limiting factor on the salt marsh. In a mixed community, a moderate application of nitrogen (15 g N m –2 year –1 as NH 4 -NO 3 ) promoted growth of P. maritima and limited the biomass of S. maritima , but growth of the latter was enhanced by a high application of nitrogen (30 g N m –2 year –1 ). An increase in the abundance of annuals such as S. maritima on the salt marsh is discussed.

Evidence for concentration of anthropogenic mercury in salt marsh sediments

Sediment cores from two salt marshes, Rosário (Tagus estuary) and Laranjo (Ria de Aveiro), were analyzed for total Hg and Al, and for Fe and Mn extracted with a hydroxylamine-acetic acid solution. Both areas have been contaminated by industrial discharges during the last decades. Vertical distributions of Hg in sediments colonized by Arthrocnemum fruticosum and Halimione portulacoides were compared to profiles in non-vegetated sediments. The same vertical distribution pattern was observed in all situations: Hg enriched in sediment layers with high root density. Mercury concentrations reached 9.3 and 29.1 nmol g–1 in Rosário, and 149.0 and 196.0 nmol g–1 in Laranjo. At both marshes, higher concentrations were found in sediments colonized by H. portulacoides. These values are one order of magnitude above the levels found in nonvegetated sediments. Mercury was enriched in sediment layers containing high concentrations of Fe extracted with a hydroxylamine-acetic acid solution, indicating the importance of Fe (and Mn) oxides formed in the rooting sediments for the retention of anthropogenic Hg.

Food preferences of Shorelarks Eremophila alpestris, Snow Buntings Plectrophenax nivalis and Twites Carduelis flavirostris wintering in the Wadden Sea

Capsule Seeds of plants from lower salt marsh communities are preferred, with insects less important. Methods Droppings of Shorelarks Eremophila alpestris, Snow Buntings Plectrophenax nivalis and Twites Carduelis flavirostris sampled in the German Wadden Sea were analysed and compared with food abundance to assess preferences. Results Shorelarks prefer seeds of Salicornia sp., Suaeda maritima, Atriplex sp., Halimione portulacoides and unidentified small grass seeds. Insects are eaten mainly in periods of seed shortage, but are consumed in smaller amounts during the winter. The food composition of Snow Buntings is very similar, but additionally Triglochin maritimum is commonly eaten. Twites are specialized on seeds of Salicornia sp. and Suaeda maritima and rarely ingest other seeds and insects. All seeds consumed were of plants from lower salt marsh communities. Many halophyte seeds, and especially those that birds feed on, are rich in energy. Large seeds and those which need a long handling time are avoided. Conclusion Changes in the lower salt marshes of the Wadden Sea by embankments and intensified grazing might have been responsible for the rapid population decline from the 1960s to 1980s.

Drainage and Elevation as Factors in the Restoration of Salt Marsh in Britain

AbstractIntertidal restoration through realignment of flood defenses has become an important component of the U.K. coastal and estuarine management strategy. Although experimentation with recent deliberate breaches is in progress, the long‐term prognosis for salt marsh restoration can be investigated at a number of sites around Essex, southeast England where salt marshes have been reactivated (unmanaged restoration) by storm events over past centuries. These historically reactivated marshes possess higher creek densities than their natural marsh counterparts. Both geomorphology and sedimentology determine the hydrology of natural and restored salt marshes. Elevation relative to the tidal frame is known to be the primary determinant of vegetation colonization and succession. Yet vegetation surveys and geotechnical analysis at a natural marsh, where areas with good drainage exist in close proximity to areas of locally hindered drainage at the same elevation, revealed a significant inverse relationship between water saturation in the root zone and the abundance of Atriplex portulacoides, normally the physiognomic dominant on upper salt marsh in the region. Elsewhere in Essex natural and restored marshes are typified by very high sediment water contents, and this is reflected in low abundance of A. portulacoides. After a century of reestablishment no significant difference could be discerned between the vegetation composition of the storm‐reactivated marshes and their natural marsh counterparts. We conclude that vegetation composition may be restored within a century of dike breaching, but this vegetation does not provide a reliable indicator of ecological functions related to creek structure.

Croissance de juvéniles de Nereis diversicolor nourris avec des détritus d’halophytes

The comparative effect of the uptake of fresh and degraded detritus of halophytic plants, harvested from salt marches of the Mont Saint-Michel Bay (France), on the growth of a juvenile population of the annelid polychaete N. diversicolor (L.) was studied under experimental conditions in summer 1993. Fresh and degraded detritus of Spartina anglica, Halimione portulacoides and Salicornia europeae, as well as the green algae Enteromorpha sp. were distributed separately to homogenous set of juveniles for a 75 d period. The highest growth rate was obtained for worms fed with Enteromorpha sp. Administration of fresh detritus of a given halophyte species to N . diversicolor juveniles always leads to a significantly higher growth rate than did degraded detritus. This is probably due to a great microbial biomass occurring on the fresh detritus, which is moreover, much better assimilated than the detritus they colonize.

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.

Directional and non‐directional vegetation changes in a temperate salt marsh in relation to biotic and abiotic factors

Abstract. The effects of reduction and cessation of sheep grazing on salt‐marsh vegetation were studied on a formerly intensively grazed salt marsh in northern Germany. Plant species cover was recorded in 45 permanent plots from 1992 to 2000. In 1995, physical and chemical soil parameters were analysed. Results of Redundancy Analysis (RDA) indicated that salinity and the depth of anoxic conditions below the surface were the most important soil factors related to the spatial vegetation pattern. Furthermore, plant species distribution was influenced by present and past grazing intensity, by soil grain size and nitrogen content.Vegetation changes over 9 yr were analysed by non‐linear regression. The cover of Aster tripolium, Atriplex portulacoides, and, to a lesser extent, Artemisia maritima and Elymus athericus increased due to reduced grazing pressure, whereas the cover of Salicornia europaea decreased. After a strong increase in the first years Aster decreased 2 to 6 yr after abandonment. In the mid salt‐marsh zone Puccinellia maritima was replaced by Festuca rubra. The cover of Puccinellia, Festuca, Suaeda maritima, Glaux maritima and Salicornia fluctuated strongly, probably due to differences in weather conditions and inundation frequency. Species richness per 4 m2 generally increased while vegetation evenness decreased during the study period. Only in the high salt marsh abandoned for 9 yr did the number of species decrease slightly. Thus far, cessation of grazing did not lead to large‐scale dominance of single plant species.

The role of spatio‐temporal heterogeneity in the establishment and maintenance of Suaeda maritima in salt marshes

Abstract. The effects of disturbance and microtopography on the organization and dynamics of plant communities were studied in a European salt marsh located in the Bay of Mont St. Michel, France. The existence of seed trapping mechanisms was also tested. The study took place in the lower and middle marsh plant communities dominated by the perennials Puccinellia maritima and Halimione portulacoides, respectively and associated with the annual Suaeda maritima. Three treatments were used in series of plots placed in each community: (1) vegetation removal and root destruction to a depth of 10 cm and refilling, (2) non‐remnant herbicide treatment without vegetation removal and (3) creation of depressions (20 cm deep). These treatments were compared with adjacent control plots. The first year of the experiment showed that the perennials facilitated the establishment of Suaeda by trapping its seeds. Estimation of cover, density and biomass over 5 yr following the disturbances showed that in the first 2 yr Suaeda dominated the disturbed plots. Thereafter Suaeda was gradually eliminated by competitive exclusion after ca. 3 yr in the zone originally dominated by Puccinellia maritima and after 4 yr in the zone occupied by Halimione portulacoides. Depressions constituted refuge habitats for Suaeda by limiting competition with the perennials but also led to a high risk of mortality with temporal fluctuations in density. Despite a period of investigation limited to 5 yr, our study demonstrated that natural disturbances of various types occurred and influenced the dynamics of Suaeda, Halimione and Puccinellia. We deduced that natural disturbances and microtopography are responsible for the maintenance of the habitat in a state of non‐equilibrium by favouring the establishment of both spatial and temporal environmental heterogeneity. These conditions appear to be particularly favourable for the maintenance of annual species such as Suaeda maritima.

The role of spatio‐temporal heterogeneity in the establishment and maintenance of Suaeda maritima in salt marshes

Abstract The effects of disturbance and microtopography on the organization and dynamics of plant communities were studied in a European salt marsh located in the Bay of Mont St. Michel, France. The existence of seed trapping mechanisms was also tested. The study took place in the lower and middle marsh plant communities dominated by the perennials Puccinellia maritima and Halimione portulacoides, respectively and associated with the annual Suaeda maritima. Three treatments were used in series of plots placed in each community: (1) vegetation removal and root destruction to a depth of 10 cm and refilling, (2) non‐remnant herbicide treatment without vegetation removal and (3) creation of depressions (20 cm deep). These treatments were compared with adjacent control plots. The first year of the experiment showed that the perennials facilitated the establishment of Suaeda by trapping its seeds. Estimation of cover, density and biomass over 5 yr following the disturbances showed that in the first 2 yr Suaeda ...

Directional and non‐directional vegetation changes in a temperate salt marsh in relation to biotic and abiotic factors

The effects of reduction and cessation of sheep grazing on salt-marsh vegetation were studied on a formerly intensively grazed salt marsh in northern Germany. Plant species cover was recorded in 45 permanent plots from 1992 to 2000. In 1995, physical and chemical soil parameters were analysed. Results of Redundancy Analysis (RDA) indicated that salinity and the depth of anoxic conditions below the surface were the most important soil factors related to the spatial vegetation pattern. Furthermore, plant species distribu- tion was influenced by present and past grazing intensity, by soil grain size and nitrogen content. Vegetation changes over 9 yr were analysed by non-linear regression. The cover of Aster tripolium, Atriplex portulacoides, and, to a lesser extent, Artemisia maritima and Elymus athericus increased due to reduced grazing pressure, whereas the cover of Salicornia europaea decreased. After a strong increase in the first years Aster decreased 2 to 6 yr after abandonment. In the mid salt-marsh zone Puccinellia maritima was replaced by Festuca rubra. The cover of Puccinellia, Festuca, Suaeda maritima, Glaux maritima and Salicornia fluctuated strongly, probably due to differences in weather conditions and inunda- tion frequency. Species richness per 4 m 2 generally increased while vegetation evenness decreased during the study period. Only in the high salt marsh abandoned for 9 yr did the number of species decrease slightly. Thus far, cessation of grazing did not lead to large-scale dominance of single plant species.