Puccinellia Phryganodes Research Articles

Accumulation Characteristics of Metals and Metalloids in Plants Collected from Ny-Ålesund, Arctic

Toxic elements can be transported to polar regions by long-range atmospheric transport from mid and low latitudes, leading to enrichment of elements in the polar environment, especially in the Arctic. The plants can be ideal bioindicators of element contamination in environments, but information on the element enrichment and sources of plants remains limited in polar regions. Here, concentrations of 15 metals and metalloids (Pb, Ni, Cr, Cu, Co, As, Cd, Sb, Hg, Se, Fe, Zn, Mn, Al, and Ti) in six species of plants, Deschampsia caespitosa (Tufted Hair Grass), Puccinellia phryganodes (Creeping Alkaligrass), Saxifraga aizoides (Yellow Mountain Saxifrage), Dicranum angustum (Dicranum Moss), Salix Polaris (Polar Willow), and Cerastium arcticum (Arctic Mouse-Ear Chickweed), collected from Ny-Ålesund, the Arctic, were determined, and enrichment and sources of elements were assessed. Results show that element concentrations vary in different plant species, and element levels in D. angustum and C. arcticum are generally higher. In spatial terms, elevated element concentrations were found near residential areas, while low element levels were present at the sites far from settlement points. Enrichment assessment shows that Cd, Hg, and Zn are the most enriched elements, with enrichment factors above 30, suggesting sources other than soil dust control their concentrations. Principal component analysis (PCA) showed that the extracted three components can explain 82% of the total variance in element concentrations. The elements Ni, Cr, As, Sb, Fe, Al, Ti, and to a lesser extent Co are highly loaded in PC1, possibly associated with continental crust particles. PC2 is closely correlated with Cd, Se, Mn, Cu, and Zn, while Hg and Pb have high loadings on PC3. The elements highly loaded on PC2 and PC3 are likely associated with pollutants from atmospheric transportation. Together with enrichment assessment, the investigated plants have a great potential for monitoring atmospheric Cd, Hg, and Zn pollution in Ny-Ålesund, and D. angustum and D. caespitosa are the more sensitive species. The results would be of significance for monitoring element contamination in the pristine Arctic environments using the bioindicator plants.

Habitat change at a multi-species goose breeding area on Southampton Island, Nunavut, Canada, 1979–2010

Foraging by hyperabundant Arctic-nesting geese has significant impacts on vegetation of Arctic and subarctic coastal lowlands, but long-term data sets documenting these changes are rare. We undertook intensive surveys of plant communities at East Bay and South Bay, Southampton Island, Nunavut, Canada, in July 2010. Lesser Snow Geese, Ross’s Geese, Cackling Geese, and Brant nest and rear young at these sites; the first three have experienced up to 10-fold increases since the 1970s. At East Bay, we found significant declines in graminoids over the 31-year span, as well as significant declines in lichen and willow cover, and significant increases in rock cover. Transect data indicated graminoids were present at only 15%–36% of points at East Bay, whereas at South Bay, graminoids were present at 28%–90% of points. Moss was more prominent in transects at South Bay than at East Bay (40%–85% vs. 19%–42%), but quadrat data indicated much more of the moss cover at South Bay apparently was dead than at East Bay. Puccinellia phryganodes (Trin.) Scribn. & Merr. exceeded 1% in only two transects. Our data demonstrate a striking decline of preferred forage species and increases in non-forage cover, consistent with the hypothesis that changes resulted from persistent long-term foraging by the four species of breeding geese between spring arrival and late summer departure.

A climatic relict or a long distance disperser: conservation genetics of an Arctic disjunct polyploid plant

The Primula sibirica group is a set of approximately a dozen Arctic, taxonomically unrelated plant species that share a similar disjunct distribution on the shores of the Arctic Ocean and the northernmost part of the Baltic Sea. The origin of this phylogeographic pattern is not known. It has been suggested, first, that the species arrived after the last glaciation from the White Sea, second, that they are relicts of once larger populations or, third, that they arrived via jump dispersal. One of the species is the polyploid Creeping alkali grass, Puccinellia phryganodes, which is critically endangered in Finland. Here we used microsatellite markers to study seven extant and three extinct populations from coasts of the Bothnian Bay and the Arctic Sea (N = 297). We estimated the genetic diversity in the study populations and applied principal component analysis and Bayesian and coalescence methods to examine their population genetic structure and evolutionary history. We found that the endangered Bothnian Bay population still harbors a reasonably high amount of genetic diversity and is differentiated from the geographically closest populations. We show that Puccinellia phryganodes is more likely a climatic relict in the Bothnian Bay than a long-distance disperser and that the endangered southern population should be considered as an evolutionary significant unit rather than a mere representative of the main population.

Coasts of Foxe Basin, Arctic Canada

Abstract Foxe Basin is a down-faulted arctic basin floored by Palaeozoic carbonates, surrounded by metamorphic Precambrian terrains. Quaternary deposits consist of Pleistocene–Holocene glacial drift, and frost-shattered bedrock-clasts mostly reworked by sea waves during post-glacial emergence during the last 5000–6000 yr. The shallow, primarily micro- to meso-tidal sea is covered by ice for c. 9–10 months each year. This ensures that the overall energy of the coasts is low, although strong storm waves develop during ice-free periods. Puccinellia phryganodes dominated salt marshes occur on muddy and sandy shores and grade into inland sedge-forb wetlands and Dryas -dominated tundra. Cold climate processes active on the emerged land have generated typical features such as frost heaving of bedrock blocks, solifluction lobes on slopes, frost boils in flatter areas, frost shattering and solution of surficial carbonate pebbles, thermokarst lakes, and shallow Cryosols.

Decadal changes in vegetation of a subarctic salt marsh used by lesser snow and Canada geese

In the Hudson–James Bay system, grubbing and grazing by lesser snow geese have resulted in severe devegetation of coastal marshes. These changes likely represent an example of an alternative stable state; however, long-term datasets documenting whether revegetation is occurring are scarce. Here, we report results of a 10-year study investigating changes in the state of a degraded salt marsh system on the north coast of Akimiski Island, Nunavut. Four transects were intensively sampled in 1998 and 2008, two within the dense nesting and brood-rearing area of a snow geese colony, one on the colony edge, and one outside it; all of these sites were also used by broods of Canada geese. Key forage species (Puccinellia phryganodes, Festuca rubra, Carex subspathacea) were less common near the colony center than elsewhere; biomass of Puccinellia also tended to be lower in more central areas. Forage species often increased in abundance between samplings, but the magnitude of changes was small. In contrast, non-forage species (Salicornia, Spergularia, Glaux) often reached high abundance within the colony center; some (Salicornia) decreased while others (Spergularia) increased. We argue the degraded state was initiated by foraging damage from an exceptional stopover of 295,000 staging birds in 1972 and that the combined foraging pressure of relatively small numbers of nesting and migrant geese since then, coupled with soil changes, has been sufficient to maintain devegetated areas as a persistent alternative state. Whether or not this state is truly stable, further recovery is likely to be very slow.

Seasonal partitioning of resource use and constraints on the growth of soil microbes and a forage grass in a grazed Arctic salt-marsh

Seasonal growth responses of plants and soil microorganisms to additions of nitrogen (N), phosphorus (P) and carbon (C) were examined in goose-grazed and exclosed plots in an Arctic salt marsh. Plants showed strong growth responses to N and NP additions but not to P. Nitrogen levels in the shoots and roots of Puccinellia phryganodes declined as summer progressed. Microbial biomass was low in spring in spite of N and P additions, likely due to C limitation, but values rose in autumn, independent of nutrient treatment, as dissolved organic carbon (DOC) increased. Glucose addition (C source) elicited a transitory increase in microbial biomass. Multiple plant defoliations by geese had a negative effect on microbial biomass, in spite of the presence of DOC and added N and P, possibly because hypersalinity restricted growth. Plants appear to limit soil inputs of C in summer and compete effectively for resources in contrast to autumn, indicating a temporal partitioning of resources.

Systematics of three North American polyploid arctic alkali grasses (Puccinellia, Poaceae): morphology, ploidy, and AFLP markersThis paper is one of a selection of papers published in the Special Issue on Systematics Research.

We used flow cytometry, amplified fragment length polymorphisms (AFLP), and macromorphology from field and common garden specimens to delimit and identify parental taxa of three polyploid species of Puccinellia from the North American Arctic. Tetraploid Puccinellia bruggemannii T.J. Sørensen, hexaploid Puccinellia angustata (R. Br.) E.L. Rand & Redfield, and octoploid Puccinellia andersonii Swallen were generally separable based on ploidy and AFLP pattern, and showed allopolyploid origin. All three shared AFLP bands with at least two diploids and with Puccinellia phryganodes (Trin.) Scribn. & Merr., shown here to have both triploid and tetraploid populations in Canada. Approximately 10% of hexaploid individuals had AFLP patterns that were intermediate between P. angustata and P. bruggemannii, or P. angustata and P. andersonii, and occupied corresponding intermediate positions in morphological ordinations. Geographic distributions provide better support for introgression than for multiple polyploid events to account for these intermediate patterns. In common garden experiments, half of the characters had significantly different values between field and common garden specimens, but these plastic characters varied depending on the species pair analyzed and between experiments. Moreover, several characters were significantly different among species, but these characters were also different in each of the two experiments. Given this variation, we pooled the field and common garden data to determine important key characters by discriminant analysis of species pairs.

Modification of competition between two grass species by a hemiparasitic plant and simulated grazing

Plant parasitism and herbivory are common phenomena in natural grasslands, where they may significantly affect competition between plant species. However, only few studies have simultaneously examined these two processes. We investigated whether the root hemiparasite Odontites litoralis ssp. litoralis affects the outcome of competition between two clonal graminoids, the endangered Puccinellia phryganodes and the common species Agrostis stolonifera, and whether simulated grazing affects the interaction among these three species. This study system simulates the community of early successional stages of the Bothnian Bay salt marsh meadows, which are intensively grazed by greylag geese ( Anser anser ). We conducted a factorial greenhouse experiment to study the effects of interspecific competition (one or two host species present), hemiparasitic infection (hemiparasite present or not), and simulated grazing (host clipped or not) on Puccinellia and Agrostis. Puccinellia was clearly an inferior competitor to Agrostis , whereas the two species did not differ as hosts for the hemiparasite. Infection by the hemiparasite reduced the aboveground biomass of Puccinellia and Agrostis by 59% and 45%, respectively. Competition with Agrostis decreased the biomass of parasitised Puccinellia by 36% and that of non-parasitised Puccinellia by 56%. Parasitism thus seemed to benefit Puccinellia indirectly by decreasing the relative competitive advantage of Agrostis . Moreover, parasitism increased the relative contribution of Puccinellia to the total aboveground host plant biomass. Simulated grazing decreased the aboveground biomass of Agrostis significantly more than that of Puccinellia and thus increased the competitive ability of Puccinellia . Simulated grazing of the two host species did not affect the performance of Odontites . These results suggest that both hemiparasitic plants and herbivory may play a significant role in the maintenance of plant species diversity by promoting competitively inferior species. Parasitierung und Herbivorie sind verbreitete Phänomene in natürlichen Grasländern, wo sie die Konkurrenz zwischen Pflanzenarten maßgeblich beeinflussen können. Indessen haben nur wenige Studien die beiden Prozesse gleichzeitig betrachtet. Wir untersuchten, ob der Wurzelhemiparasit Odontites litoralis ssp. litoralis das Ergebnis der Konkurrenz zwischen zwei klonalen Gräsern, der gefährdeten Art Puccinellia phryganodes und der häufigen Art Agrostis stolonifera , beeinflusst und ob sich simulierte Beweidung auf die Interaktionen zwischen den drei Arten auswirkt. Das untersuchte System bildet die Gemeinschaft der frühen Sukzessionsstadien der Salzwiesen im nördlichen Teil des Bottnischen Meerbusens nach, die intensiv von Graugänsen ( Anser anser ) beweidet werden. In einem faktoriellen Gewächshausexperiment untersuchten wir die Effekte von interspezifischer Konkurrenz (eine oder beide Wirtsarten vorhanden), des Befalls mit dem Hemiparasiten (Hemiparasit vorhanden oder nicht), und von simulierter Beweidung (Wirtspflanzen beschnitten oder nicht) auf die beiden Gräser. Puccinellia war Agrostis als Konkurrent eindeutig unterlegen, während beide Arten sich als Wirte für den Hemiparasiten nicht unterschieden. Befall durch den Hemiparasiten reduzierte die oberirdische Biomasse von Puccinellia und Agrostis um 59 bzw. 45%. Konkurrenz mit Agrostis verminderte die Biomasse parasitierter Puccinellia um 36% und die von nicht parasitierter Puccinellia um 56%. Parasitierung schien deshalb Puccinellia indirekt zu begünstigen, indem der relative Konkurrenzvorteil von Agrostis reduziert wurde. Außerdem erhöhte die Parasitierung den relativen Beitrag von Puccinellia zur oberirdischen Gesamt-Pflanzenbiomasse. Simulierte Beweidung verringerte die oberirdische Biomasse von Agrostis signifikant stärker als die von Puccinellia und stärkte somit die Konkurrenzkraft der zweiten Art. Die simulierte Beweidung der Wirtsarten beeinflusste die Performanz von Odontites nicht. Diese Ergebnisse legen nahe, daß sowohl hemiparasitische Pflanzen als auch Beweidung eine wichtige Rolle bei der Erhaltung der Artenvielfalt der Pflanzen spielen können, indem unterlegene Konkurrenten gefördert werden.

Management of three endangered plant species in dynamic Baltic seashore meadows

AbstractQuestion: Arctophila fulva var. pendulina, Primula nutans var. jokelae and Puccinellia phryganodes are threatened early successional species growing in the seashore meadows of the northern Baltic Sea. Patches formed by these species are destined to be replaced by other species during primary succession and in order to persist in the area they have to continuously colonize new areas. We studied whether the displacement of the species could be slowed down and their sexual and/or vegetative reproduction enhanced by management targeted to surrounding vegetation.Location: Bothnian Bay, Baltic Sea, W Finland.Methods: Vegetation surrounding patches of all study species was mown in four successional growing seasons. Moreover, the impact of additional soil turning on creating new favourable growing sites was tested for A. fulva.Results: Deterioration of suitable habitats of A. fulva and P. nutans was markedly slowed down by management and the vegetative and/or sexual reproduction of these species was enhanced. In the case of P. phryganodes, however, no positive response to management was obtained.Conclusions: In order to improve the long‐term persistence of these three species successional vegetation changes should be slowed down and their dispersal and colonization success improved by continuous management of the populations. We further suggest that the colonization of new areas should be aided by transplantations to the non‐vegetated islets, which have recently risen from the sea and cannot be reached by means of dispersal.

Vegetation loss alters soil nitrogen dynamics in an Arctic salt marsh

Summary Plant and microbial nitrogen (N) dynamics were examined in soils of an Arctic salt marsh beneath goose‐grazed swards and in degraded soils. The degraded soils are the outcome of intensive destructive foraging by geese, which results in vegetation loss and near‐irreversible changes in soil properties. The objective of the study was to determine whether vegetation loss led to a decline in microbial activity and a redistribution of N amongst the different soil N pools that potentially could adversely affect plant regrowth. In situ N allocation between plants, microbes and soil was determined based on injection of 15NH4Cl into soil cores; changes in isotopic ratios and N concentrations in the different pools were measured after 24 h. Degraded soils, in contrast to vegetated soils, were characterized by a decline in microbial biomass, reduced microbial 15N excess, reduced rates of gross N immobilization and an increased microbial residency time of 15N. In vegetated soils, both microbes and the forage grass, Puccinellia phryganodes, accumulated 15N such that little remained in the soil abiotic phase after 24 h, unlike in degraded soils. The decline in microbial activity in degraded soils may be linked to a low availability of soil carbon in the absence of plants and to deteriorating abiotic conditions, including the occurrence of hypersalinity in summer. Not all biotic processes respond similarly to the change in ecosystem state. Unlike vascular plant productivity and goose foraging which are absent in degraded soils, soil microbial activity is maintained, albeit at a lower level. In spite of this activity, the greater proportion of 15N in degraded soils is in the abiotic pool rather than in microbial biomass with an increased potential for soil N loss from leaching and soil erosion. Disturbance linked to herbivory often triggers catastrophic shifts in ecosystem properties resulting in vegetation loss and changes in soil biogeochemical cycling that are irreversible, at least on a decadal time scale, and lead to the loss of N and other nutrients required for plant growth. These results clearly illustrate that microbial activity does not compensate for the effects of plant removal on soil N retention.

Nutrient limitation of plant growth and forage quality in Arctic coastal marshes

Summary Foraging by geese has led to vegetation loss in salt marshes along the Hudson Bay coast and lesser snow geese are increasingly grazing inland freshwater marshes. We determined whether different nutrients limit the growth of forage plants in the two habitats, and whether these differences affect the nutritional quality of vegetation available to geese at La Pérouse Bay, Manitoba. Results from fertilization experiments indicate that primary productivity in the salt marsh is both nitrogen and phosphorus limited, whereas the freshwater marsh is phosphorus limited. Total amounts of calcium, magnesium and potassium in above‐ground biomass per unit area showed similar differences in limitation. Leaves of preferred forage species have higher nutrient concentrations (nitrogen, phosphorus, calcium, potassium, magnesium, sodium) and lower C : N and C : P ratios than alternative forage. The main forage species in the salt marsh (Puccinellia phryganodes) has higher nutrient content per unit mass, for nitrogen, magnesium, calcium and sodium, than the major freshwater marsh species(Carex aquatilis). The difference in nutritional quality of forage between the marshes is likely to have had consequences for goose fitness, and may have contributed to the reported declines in gosling survivorship and size. At moderate grazing intensities, seasonal growth of salt‐marsh forage is maintained by addition of nitrogen and, to a lesser extent, phosphorus from high numbers of goose faeces to swards. In contrast, the low densities and low phosphorus content of goose faeces in the phosphorus‐limited freshwater marsh mean that plants are unlikely to recover rapidly from the effects of grazing. As a consequence, the freshwater marsh is likely to become increasingly less productive as foraging intensifies. Nutrient gradients in vegetation across an ecotone and changes in foraging behaviour have resulted in adverse effects on both the growth rates of individuals and the population structure of a herbivore.

Initiation and maintenance of vegetation mosaics in an Arctic salt marsh

Summary 1 Vegetation mosaics of grassland and exposed soil are often the outcome of intense herbivory and represent alternate stable states, although the vegetational and soil processes that both initiate and maintain the states in response to herbivory are poorly understood. 2 The vegetation mosaic resulting from grubbing by geese was examined on the intertidal flats at La Perouse Bay, Manitoba. Soil properties of the alternate states were measured in conjunction with the ability of transplanted tillers of Puccinellia phryganodes to grow in exposed soil and intact swards. Simulated grubbed patches (2.5–40 cm diameter) were prepared at three sites and the soil properties and inward clonal growth of the grass in each patch were examined during two growing seasons. 3 Where an organic layer was still present on exposed areas, soil properties were similar to those in the rooting zone beneath intact swards, except that soils were hyper-rather than hyposaline. Older exposed mineral soils, where the organic layer had been eroded, were similarly hypersaline, but were also low in soil moisture and total nitrogen, and compacted with a low infiltration rate. Transplanted tillers survived in intact swards, but few survived in any hypersaline soils. 4 Changes in soil properties over two seasons depended on size of experimentally created patches. Again, high salinities developed in soils of the larger patches, and there was a loss of nitrogen and soil moisture and an increase in bulk density with increasing patch size. Although inward clonal growth of P. phryganodes took place from plot perimeters, this is likely to be curtailed by high salinities in plots over 20 cm diameter. 5 As in tropical Africa, intense herbivory can lead to an alternate stable state in this Arctic salt marsh. Small patches of exposed soil are characterized by deteriorating soil conditions and the inability of vegetation to re-establish. As patches coalesce with continued herbivory, an ecological sere (the intertidal salt marsh) is lost.

Environmental gradients, plant distribution, and species richness in arctic salt marsh near Prudhoe Bay, Alaska

Spatial patterns of plant cover and species composition in arctic salt marsh and salt affected tundra near Prudhoe Bay, Alaska reflect gradients in elevation, soil conductivity, and soil concentrations of the ions prevalent in seawater. Soil conductivity and soil concentrations of Ca2+, Mg2+, Na+, K+, SO4= and Cl− were significantly related to site elevation, decreasing as elevation increased. Vascular plant species richness increased significantly as soil conductivity and soil ion concentrations decreased, and site elevation increased. Puccinellia phryganodes was the only species present in low elevation sites with low plant cover, high soil conductivity and high soil concentrations of Ca2+, Mg2+, Na+, K+, SO4= and Cl−. Mid-gradient sites were dominated by Carex subspathaceae. Plant cover at these sites was greater than at lower elevation sites, but bare ground was still present. Higher elevation sites had the lowest concentrations of soil ions and the lowest soil conductivities. These sites had little bare ground, contained as many as 16 species, and were dominated by Dupontia fischeri and Eriophorum angustifolium. Ordinations indicated that a complex topographic gradient related most closely to elevation and site distance from the coast best explains variation in the vegetation cover. Irregular deposition along the coastline partially or completely buried three sites in peat or sand up to 20 cm deep. Such rapid changes in plant cover and species composition contributes to the community patch mosaic typical of these marshes. Results suggest an individualistic response of plant species to the environmental gradients in salt marsh and salt affected tundra and are indicative of successional models developed in other marginal arctic environments.

Interactions in the uptake of amino acids, ammonium and nitrate ions in the Arctic salt‐marsh grass, Puccinellia phryganodes

ABSTRACTThe uptake of amino acids and inorganic nitrogen by roots of Puccinellia phryganodes was examined to assess the potential contribution of soluble organic nitrogen to plant nitrogen uptake in Arctic coastal marshes, where free amino acids constitute a substantial fraction of the soil‐soluble N pool. Short‐term excised root uptake experiments were performed using tillers grown hydroponically under controlled conditions in the field. The percentage reductions in ammonium uptake at moderate salinity (150 mm NaCl) compared with uptake at low salinity (50 mm NaCl) were double those of glycine, but glycine uptake was more adversely affected than ammonium uptake by low temperatures. Glycine uptake was higher at pH 5·7 than at pH 7·0 or 8·2. The glycine uptake was up‐regulated in response to glycine, whereas ammonium uptake was up‐regulated in response to ammonium starvation. Nitrate uptake was strongly down‐regulated when tillers were grown on either ammonium or glycine. In contrast to N‐starved roots, which absorbed ammonium ions more rapidly than glycine, the roots grown on glycine, ammonium and nitrate and not N‐starved prior to uptake absorbed glycine as rapidly as ammonium and nitrate ions combined. Overall, the results indicate that amino acids are probably an important source of nitrogen for P. phryganodes in Arctic coastal marshes.

Free amino acid, ammonium and nitrate concentrations in soil solutions of a grazed coastal marsh in relation to plant growth

AbstractSoluble free amino acids, ammonium and nitrate ions as sources of nitrogen for plant growth were measured in soils of a coastal marsh grazed by snow geese in Manitoba, Canada. Amounts of nitrogen, primarily ammonium ions, increased in the latter half of the growing season and over winter, but fell to low values early in the growing season. Free amino acid concentrations relative to ammonium concentrations were highest during the period of rapid plant growth in early summer, especially in soils in the intertidal zone, where the median ratio of amino acid nitrogen to ammonium nitrogen was 0·36 and amino acid concentrations exceeded those of ammonium ions in 24% of samples. Amino acid profiles, which were dominated by alanine, proline and glutamic acid, were similar to goose faecal profiles. In a continuous flow hydroponic experiment conducted in the field, growth of the salt‐marsh grass, Puccinellia phryganodes, on glycine was similar to growth on ammonium ions at an equivalent concentration of nitrogen. When supplies of soil inorganic nitrogen are low, amino acids represent a potentially important source of nitrogen for the re‐growth of plants grazed by geese and amino acid uptake may be as high as 57% that of ammonium ions.

Patterns of vegetation change and the recovery potential of degraded areas in a coastal marsh system of the Hudson Bay lowlands

Summary In recent decades, foraging by increasing numbers of lesser snow geese has led to loss of vegetation and changes in soil conditions in marshes on the Hudson Bay coast. Changes in species composition were recorded in areas unprotected from goose foraging and in exclosures of varying age (5–15 years) erected in intact swards and on bare sediments where foraging had occurred at La Pérouse Bay, Manitoba. In the supratidal marsh, plants failed to establish naturally in either open or exclosed (15 years) plots in bare areas. In moist intertidal soils, vegetative fragments of the asexual species Puccinellia phryganodes readily established and formed a mat in exclosures (5 years). Changes in species assemblages occurred over 11 years in exclosed and adjacent open plots in intertidal and supratidal marshes. Loss of vegetation cover and species richness, particularly dicotyledonous species, and the reversion of later successional plant assemblages to earlier successional assemblages occurred in open plots. In the absence of foraging, late successional graminoids and willow species replaced early successional graminoids. Late successional grasses of the upper intertidal marsh died when transplanted into degraded soils but still survived after one season in control plots, suggesting that an early successional template is needed for establishment. In the absence of goose foraging, natural re‐vegetation by clonal propagation can occur only where edaphic conditions are suitable. Within exclosures, vegetation changes resemble those in undamaged areas where goose foraging pressure is still moderate. We propose a state and transition model for vegetation change in the system based on succession patterns, alternative vegetation states and geomorphological events.

Assisted revegetation trials in degraded salt‐marshes

Summary1. At coastal sites adjacent to the Hudson Bay lowlands, intensive foraging by increasing numbers of lesser snow geeseAnser caerulescens caerulescenshas converted salt‐marsh swards to hypersaline mudflats largely devoid of vegetation. Assisted revegetation trials were undertaken in order to determine the ability of plants to establish in degraded salt‐marsh sediments.2. Soil plugs of the former dominant graminoids,Puccinellia phryganodesandCarex subspathacea, were transplanted into plots of hypersaline bare soil. Some plots were treated with fertilizer and peat mulch to determine if ameliorations enhance plant growth.3. Transplants ofP. phryganodesestablished in degraded sediments, but those treated with fertilizer and peat showed significantly higher growth than those in bare soil after two growing seasons. The ratio of the mean basal area of plants in treated plots compared with bare plots was between 1·7 and 4·0 : 1 at different sites. Transplants ofC. subspathaceadid not establish readily in degraded sediments and no growth enhancement was observed with soil amendments.4. Growth rate and mortality of plants both varied between sites and years, reflecting variation in the frequency of hot, dry weather from late June to early August of each year, and the salinity and water content of soils during that period. The potential for revegetation of mudflats is discussed in the context of the soil degradation processes. Fine‐grain variation in soil conditions presents a major challenge for the restoration of plant assemblages in these coastal marshes.5. The extent of soil degradation and of vegetation loss makes it unlikely that unassisted revegetation will occur at some sites, even in the absence of goose foraging, without erosion of consolidated sediments and the establishment of plant assemblages in fresh unconsolidated sediments.

The vegetation types of Northeast Greenland. A phytosociological study based mainly on material left by Th. Sørensen from the 1931-35 expeditions

Based on 347 vegetation analyses carried out in 1931-35 by Th. S0rensen in the 72°- 74°N area, supplemented by 136 recent analyses from 74½0N and field observations northwards to 79°N, the vegetation types of Northeast Greenland are described. Further to phanerogams, the mosses and a few lichens are determined in 274 of the 347 analyses.
 The most characteristic vegetation types present in this middle-arctic area are: 1. Dwarfshrub heaths dominated by Cassiope tetragona, Salix arctica, Vaccinium uliginosum ssp. microphyllum or Betula arctica, depending on soil and duration of snow cover. 2. Grasslands, drying out during summer, characterised by Arctagrostis latifolia, Carex bigelowii, C. misandra, and Eriophorum triste. 3. Permanently wet fens with Carex stanus, Eriophorum scheuchzeri, and Arctagrostis latifolia. 4. Snowbeds, the late ones characterised by Phippsia algida, the moderately late by Salix herbacea, and the few early herb-slope like snowbeds by Trisetum spicatum and Erigeron humilis. 5. Open, graminoid Dryas-heaths and fell-fields on dry soil with Carex nardina, C. rupestris, and Kobresia myosuroides. 6. Fell-fields with Calamagrostis purpurascens and Carex supina ssp. spaniocarpa. 7. Species rich communities on wet ground, covered by organic crust, characterised by Koenigia islandica and Festuca hyperborea. 8. Halophytic vegetations with Puccinellia phryganodes and Carex subspathacea.
 Soil samples have been analyzed for nine factors for the major part of the 347 analyses. The plant to soil relationship is illustrated for the 109 most frequent phanerogam species, for 40 of these lo all nine factors, for 69 only to pH and conductivity. 
 Sørensen arranged his analyses in 41 phytosociological groups according to his similarity coefficient - the "Sørensen index''. These groups form the basis of the phytosociological classification according to the Braun-Blanquet system. The vegetation units are grouped into 13 associations, of which 7 are new, subdivided into a number of new, lower phytosociological units. These are grouped in the alliances Saxifrago-Ranunculion nivalis, Caricion atrofusco-saxatilis, Dryadion integrifoliae, Veronico-Poion glaucae, and Puccincllion phryganodis. Two synoptical tables summarizes the frequency of 135 phanerogams and 99 cryptogams, mainly mosses, in 42 phytosociological units.

A Positive Feedback: Herbivory, Plant Growth, Salinity, and the Desertification of an Arctic Salt-Marsh

1 A 2-year study is described which suggests that a positive feedback process results in the destruction of salt-marsh swards and the exposure of bare sediments at La Perouse Bay, Manitoba, Canada. Lesser snow geese initiate the process by grubbing for roots and rhizomes of salt-marsh graminoids (Puccinellia phryganodes and Carex subspathacea) in spring. The increased rates of evaporation from sediments beneath disturbed or destroyed swards in summer result in high soil salinities that adversely affect the growth of the remaining grazed plants. 2 Above-ground biomass and soil salinity differed between sites in the salt marsh. Soil salinity was inversely related to above-ground biomass and shoot density of Puccinellia phryganodes. Increased biomass led to reduced soil salinity at sites where exclosures were erected. 3 Plant growth, measured as the rate of leaf births on Puccinellia shoots, was reduced by high soil salinities at sites where exclosures were erected. 4 Leaf demography of transplanted experimental plants of Puccinellia differed in 1992, but not 1991, between plants transplanted into sites with different amounts of above-ground biomass. Leaf births and deaths were highest for plants grown in sites where above-ground biomass was high and lowest for plants transplanted into bare sites. Grazing had no effect on leaf demography in 1991 and only marginally increased the rate of leaf deaths in 1992. 5 Growth of transplanted individuals of Carex subspathacea was similarly highest at sites where the standing crop of Puccinellia and Carex was high and was lowest in bare sites. 6 Algal crusts, which formed on bare or poorly vegetated sites, also reduced the growth of Puccinellia plants. 7 The effects of this deleterious positive feedback on plant growth are discussed in relation to changes occurring in the lesser snow goose colonies at La Perouse Bay and elsewhere.

The Effect of Salinity on the Leaf and Shoot Demography of Two Arctic Forage Species

1 Two important graminoid forage species, Puccinellia phryganodes and Carex subspathacea, which are eaten by lesser snow geese, are widespread in arctic coastal salt marshes. Extensive grubbing of these plants by geese has led to increased soil salinity which may restrict their regrowth, particularly for the sedge which grows in less saline sites. 2 The effects of salinity on leaf and shoot birth and death rates and on mortality of plants of the two species were therefore examined when pot-grown plants of Puccinellia were exposed to different salinities under field conditions at La Perouse Bay, Manitoba. A similar experiment on Puccinellia was also conducted in a growth chamber. 3 Leaf death rates increased with salinity and approached or exceeded leaf births at the highest salinities (40-80 g L` dissolved salts containing sodium at a concentration between 568 mol m-3 and 1136 mol m-3). The salinities at which these changes were evident depended on the species and the growing conditions. When birth and death rates of leaves and plant deaths were compared, Puccinellia phryganodes was less saltsensitive than Carex subspathacea. 4 As salinity increased, the decline in numbers of leaf births on axillary shoots and attached tillers of plants of Puccinellia and Carex was faster than the decline in leaf births on main shoots. 5 The growth responses of the two species to salinity are discussed in relation to the foraging activities of the geese and the long-term changes occurring in salt marshes on the coast of Hudson Bay.