Embryo Dunes Research Articles

Facilitation of Leymus mollis by Honckenya peploides on coastal dunes in subarctic Quebec, Canada

Plant recruitment in the very first stages of primary succession is limited by seed availability and harsh abiotic conditions. Facilitation, the positive effect of an earlier successional species on a later successional one, is often significant during primary succession and may result from the trapping of seeds and (or) the improvement of seed germination, seedling emergence, establishment, growth, and survival. We examined the effect of mature Honckenya peploides (L.) Ehrh. (Caryophyllaceae) plants on Leymus mollis Trin. (Poaceae) seedling recruitment on a coastal dune in subarctic Quebec, Canada. Facilitative effects of H. peploides on L. mollis may be critical because the latter species is a key element in the dynamics of the coastal dunes at high latitudes in eastern Canada. Honckenya peploides forms small mounds on the upper beach (the embryo dunes) that are typically distinct from the foredune. Leymus mollis progression towards the upper beach occurs through clonal growth, but seedling recruitment is also significant and contributes to the population genetic diversity. We determined L. mollis seedling emergence and growth and estimated various abiotic variables in two habitats on the upper beach: the embryo dunes and the bare, flat areas beside embryo dunes. Sand accumulation and substrate salinity were higher on the embryo dunes than beside them. Leymus mollis seedling emergence was more important on embryo dunes, although seedling growth was lower there. Our results suggest that the embryo dunes formed by H. peploides facilitate L. mollis recruitment possibly by trapping seeds and improving seed germination and seedling emergence.Key words: coastal dunes, facilitation, Honckenya peploides, interspecific interactions, Leymus mollis, sand burial.

Ecophysiological differences among Leymus mollis populations across a subarctic dune system caused by environmental, not genetic, factors.

Plant species that persist during succession, from the colonization to the stabilization stages, face major environmental changes. Such changes are believed to have significant effects on species performance. In subarctic coastal dune systems, Leymus mollis colonizes the embryo dunes, on the upper limit of the beach. It reaches its maximum density on the foredune, but also grows on older, stabilized ridges. This paper reports on the phenotypic variations of some ecophysiological traits associated with the persistence of L. mollis on a dune system on the east coast of Hudson Bay (northern Quebec). Leymus mollis ramets tend to have a lower net carbon assimilation rate and water use efficiency, and a higher substomatal CO2 concentration on the stabilized dune than on the foredune. However, these physiological differences cannot be explained by differences in leaf morphology or nitrogen content. Under controlled conditions, ecophysiological differences observed in the field disappear, suggesting that these are not genetic but determined by environmental changes along the foredune-stabilized dune gradient. We propose that higher net carbon assimilation rate on the foredune might be related to higher sink strength in relation to the growth-stimulating effect of sand burial.

Persistence of colonizing plant species along an inferred successional sequence on a subarctic coastal dune (Québec, Canada)

Coastal dune systems have been extensively studied in various parts of the world, but few investigations have been made in the Subarctic where temperatures remain relatively low during the short growing season. Here, we report the results of a study performed on a subarctic coastal dune system on the east coast of Hudson Bay, Canada. We determined the spatiotemporal dynamics of some important substrate characteristics, described the spatial dynamics of the vascular plant community, and followed temporal changes in the populations of the two major plant species, Leymus mollis (Poaceae) and Lathyrus japonicus (Fabaceae), along a toposequence, from the embryo dunes to the stabilized dune. The observed spatial changes in substrate characteristics were consistent with those reported in studies of lower-latitude dune systems, but they were generally of lesser magnitude. The subarctic climate appears to have unusual effects on the spatial gradient of substrate salinity and water content. For instance, salinity did not vary along the toposequence early in the season while the bay was still partly frozen, but it showed a significant gradient during the summer, with lower salinity values on the stabilized dune. Life-form turnover, from the upper beach to the stabilized dune, was lower than what has been reported for lower-latitude dune systems because of the rarity of annual plant species. Although the density and biomass of Leymus and Lathyrus ramets decreased along the toposequence, both species persisted onto the stabilized dune where they were the most frequent vascular plants. Such persistence appears to be related to the ability of both species to physiologically adjust to local conditions. Because of the climatic context, subarctic coastal dunes constitute unique systems, with characteristics quite different from those of lower-latitude coastal dune systems.

The plant communities of a foredune in southeastern Brazil

Species composition, biomass and environmental characteristics of a coastal plant community of southeastern Brazil, was studied using data from 110 quadrats collected on the foredune of Barra de Maricá, Rio de Janeiro, Brazil. Indirect and direct gradient analyses were used to describe the foredune community. Ordination by detrended correspondence analysis (DCA) indicated the existence of three vegetation groups: pioneer, embryo dunes and a zone of fixed dunes with blow out areas. The gaps observed between groups were attributed to discontinuities in environmental factors. Most of the variation in species composition was expressed by the second axis of the DCA ordination, which was correlated with the distance from the beach bank. The second axis is interpreted as a stress gradient, with high stress in the pioneer zone decreasing to fixed dunes. The coenocline analyzed by direct gradient ordination, was divided into three segments equivalent to Groups detected by DCA ordination. The important species were: Althernanthera maritima St. Hil. in the pioneer zone, and Sporobolus virginicus (L.) Kunth, Mariscus pedunculatus (R. Brown) T. Koyama, and Mitracarpus frigidum K. Sch. in the embryo dunes. The grassPanicum racemosum (Spreng) was associated with areas of fixed dune. that were also characterized by Mollugo verciticillata L. Both biomass and species richness were lower at the high stress disturbance ends of the gradient, with their maximum value in different portions of the middle range of the gradient.Key words: detrended correspondence analysis, direct gradient analysis, foredune communities, vegetation zonation.

Luminescence dating of sediments from Buctouche Spit, New Brunswick

In this paper we describe our efforts to determine the formation chronology of a sequence of dunes on Buctouche Spit, a Holocene deposit on the northeast coast of New Brunswick. Optical dating, using infrared stimulation of K-feldspar grains, yielded ages ranging from 5 ± 30 a for an embryo dune to 765 ± 45 a for the oldest dune. Thermoluminescence ages, although less precise, support the recent formation of the dunes. The ages exhibit the expected sedation from youngest to oldest and are consistent with historical evidence coupled with an assumed constant sediment aggradation rate. The age resolution obtained was very good and we conclude that the optical dating method used here shows great promise.

Coastal sand dune vegetation of Tabasco and Campeche, Mexico

Abstract. Sand dune vegetation along the coast of the Mexican states of Tabasco and Campeche was sampled by means of 1501 releves and the data were analyzed with classification and ordination programs. 36 community types were distinguished, which were grouped into 10 higher‐order groups. The communities are described in a sequence reflecting the main vegetation zonation. Beach, embryo dune and foredune community groups include 12 community types, the sheltered zone includes 16 types and the fixed dunes 8 types. The ordination results reveal one main vegetation gradient corresponding to the increase in mean distance from the shoreline and elevation, and being covariant with species richness, mean vegetation cover and mean vegetation height.Additional differences are related to the geographical transition between the Gulf and Caribbean coastal vegetation and environmental conditions, mainly type of sand, occurring in the study area. Siliceous sand and a Gulf climate are characteristic for most of Tabasco, and calcareous sand and a Caribbean‐type climate are characteristic for Campeche.Disturbance caused by coconut plantations, cattle grazing and tourism favours the invasion of ruderal species from waste places behind the dunes, which attain local dominance in the dunes described here. Consequently some separate community types had to be distinguished.The distribution of community types is analyzed in the context of the transitions between calcareous and siliceous substrates in the study area.

Aggregation of sand from a maritime embryo sand dune by microorganisms and higher plants

The effects of the interactions between higher plants and microorganisms and the addition of selected microorganisms on aggregation of sand from an embryo dune were examined. Addition of microorganisms to sand increased both plant growth and the amount of aggregation. Roots alone had little effect on aggregation but in association with microorganisms there was a noticeable increase. The number of microorganisms isolated from aggregates in four different treatments varied each month over the course of the experiment. Aggregates from a treatment receiving Penicillium spores were colonized by the greatest number of microorganisms, and the least colonized aggregates were from a treatment where the sand was initially sterile.

Vesicular-Arbuscular Mycorrhiza in the Gramineae

VESICULAR-ARBUSCULAR mycorrhiza has been found to be widespread in cereals and in many grasses in Britain1. The incidence of root infection and the amount of endophyte mycelium on the root surface and in the rhizosphere differ greatly in different habitats and communities. For example, in sanddune grasses—where mycorrhiza is strongly developed—the degree of infection varies between different species and with the stage in the dune succession. As illustrated in Table 1, samples collected from the sand dunes at Gibraltar Point, Lincolnshire, showed about a 20 per cent level root infection when growing in the embryo dune phase, that is on sites which have never supported plant growth previously. In the next zone in the dune succession infection falls almost to zero, but it reaches a maximum where the sand becomes stabilized in the fixed yellow dunes. In this zone, where the ranges of three grasses overlap, there is marked variation in infection between the different species. As the community matures and becomes more complex, there is a general decrease in endophyte activity. Roots of grasses in the fixed yellow dunes were often extensively covered with wefts of external mycelium as well as showing a high incidence of infection.

Note on the Edaphic Succession in Some Dune Soils with Special Reference to the Time Factor

FROM the examination of a large number of samples from successive dune ridges on Blakeney Point the writer was able to demonstrate, (a) the progressive leaching of the carbonates with increasing age, (b) the passage from an alkaline to an acid condition, and (c) the progressive increase in the organic content. It was moreover shown that these changes were accompanied by changes in the flora which, broadly, consisted in diminution of calcicole species and the advent of calcifuge types'. In the Blakeney area the age of the successive dune ridges can only be inferred (except in the case of the youngest) from their relative position and it seemed therefore desirable to find some dune area where the respective ages of the dune ridges could be ascertained with a reasonable degree of accuracy. For this purpose a visit was made to the Southport dune system. The ages of the ridges in this dune system have been assessed partly by the examination of old maps (e.g. Speed's map of 1610, the Bold Estate map of 1736) and descriptions. In this way it has been possible to fix the approximate age of certain points and to establish the average rate of advance of the dunes on this coast. Secondly, the very early arrival of Salix repens in the hollows between the dune ridges makes it possible to utilise the number of annual rings in the thickest and oldest axes as a check on the estimates. In connection with the documental evidence I would record my indebtedness to the Public Library officials of Southport, whose help was ungrudgingly placed at my disposal, and to the authorities of the British Museum Library, also to W. Ashton's admirable book, The Evolution of a Coastline. The area chiefly examined was the dune series extending from Mad Wharf to Formby Golf Links and Freshfield. The youngest ridge (a) on the sea face consisted of embryo dunes scarcely coalesced, and colonised by Triticum junceum and Psamma (Ammophila) arenaria. The latter appears to be the later arrival, as is to be expected from its less halophytic characteristics. This ridge was estimated to be about two years old.

ON HOMOTYPOSIS AND ALLIED CHARACTERS IN EGGS OF THE COMMON TERN

(1) Origin of the material and method of measturement. The settlement of Common Terns, which provided material for the present work, is one of old establishment on Blakeney Point, Norfolk. This is a shingle spit of some 8 miles in length on the north coast of Norfolk, about 12 miles west of Cromer. The colony is situated on the very end of the point, with water on three sides. Here the spit is a combination of dunes, salt marsh aind shingle, and for the most part the nests are found on the openi shingle on the seaward side of the dunes. Nests are plentiful in the embryo dunes in some years, though this year (1913) none were found thiere. The colony was more scattered than usual and covered the greater part of a mile of sea front. To avoid missing any clutches, Miss K. M. Parker, B.Sc., and Mr William Rowan divided the nestinlg area into suitable well marked plots and worked these one after another. Each of these again were worked in strips, till a patch was completed, when the workers moved on to a remote one, to give the birds a chance of settling down again. After measurement each egg was numbered with indelible ink, so that any one egg was never measured twice. In all 20:3 clutches were handled.