Dune Habitats Research Articles

Impact of invasive Rosa rugosa on the arthropod fauna of Danish yellow dunes

We compared the arthropod fauna of Rosa rugosa patches to the adjacent native yellow dune vegetation by pitfall trapping in the National Park Thy at the Danish North Sea coast. R. rugosa changes the vegetation from a dune grassland (dominated by Ammophila arenaria) poor in flowering plants to a low monospecific shrubbery rich in large flowers. We predicted faunal responses according to the changes in resource availability and environmental conditions promoted by this particular invasive plant: increased populations of flower-visiting insects and species of the phytophagous and detritivorous guilds, and a decrease in thermophilic predator species. A matched-pairs sampling design allowed us to isolate the effects of the vegetation change from those of potentially confounding landscape gradients. The arthropod communities were significantly affected by the vegetation change (redundancy analysis). Six taxa (Opiliones, Lepidoptera larvae, Hymenoptera, Diptera, Tipulidae, Geotrupidae) increased in abundance, and three (Araneae, Staphylinidae, Auchenorrhyncha) were reduced in the rose patches. The main exception from predictions was the lack of effects on large detritivores (isopods, diplopods). Overall, total catches were increased by 45 % in the rose patches, primarily caused by an increase in the abundance of Diptera. Arachnids and carabid beetles were analyzed at species level: the assemblage structure was significantly affected in arachnids but not in carabids. Arachnids showed reduced species richness and diversity and increased dominance in the rose patches, due to reductions among xerotherm species. The results indicate that considerable faunistic impoverishment of thermophilic dune specialist species can be expected in the future if R. rugosa is allowed to continue its invasion across the dune habitat.

Night life on the beach: selfing to avoid pollinator competition between two sympatric Silene species.

Evolution of autonomous selfing may be advantageous because it allows for reproductive assurance. In co-flowering plants competing for pollinators, the least common and/or attractive could suffer pollen limitations. Silene niceensis and S. ramosissima are taxonomically related species sharing the same habitat, although S. ramosissima is less abundant and has a more restricted distribution. They also have the same a priori nocturnal pollinator syndrome, and show an overlapping flowering phenology. The aim of this study was to investigate whether a selfing strategy in S. ramosissima allows it to avoid pollinator competition and/or interspecific pollen transfer with S. niceensis, which would thus enable both species to reach high levels of fruit and seed set. The breeding system, petal colour, flower life span and degree of overlap between male and female phases, floral visitor abundance and visitation rates were analysed in two sympatric populations of S. niceensis and S. ramosissima in southern Spain. Autonomous selfing in S. ramosissima produced very high fruit and seed set, which was also similar to open-pollinated plants. Silene niceensis showed minimum levels of autonomous selfing, and pollen/ovule ratios were within the range expected for the breeding system. In contrast to S. niceensis, flower life span was much shorter in S. ramosissima, and male and female organs completely overlapped in space and time. Upper surface petals of both species showed differing brightness, chroma and hue. Flowers of S. niceensis were actively visited by moths, hawkmoths and syrphids, whereas those of S. ramosissima were almost never visited. The findings show that different breeding strategies exist between the sympatric co-flowering S. niceensis and S. ramosissima, the former specializing in crepuscular-nocturnal pollination and the latter mainly based on autonomous selfing. These two strategies allow both species to share the restricted dune habitat in which they exist, with a high female reproductive success due to the absence of pollinator competition and/or interspecific pollen flow.

Plant community response following the removal of the invasive Lupinus arboreus in a coastal dune system

The removal of invasive species is common in restoration projects, yet the long‐term effects of pest management programs are seldom assessed. We present results of a long‐term program to remove the invasive species Lupinus arboreus (lupin) from sand dunes in New Zealand. We evaluate the response of plant communities to lupin removal, by comparing total plant cover, the cover of non‐native and native plant species, and species richness between sand dune sites where lupin removal has occurred, not occurred, and where lupin has never been present. Neither lupin presence nor removal had a significant impact on the foredune environment. Following removal, total and other non‐native plant cover remained higher, and the cover of several native sand dune species remained lower compared with uninvaded sites in the deflation and backdune environments. These changes can be attributed to persistent effects associated with the invasion of lupin, but have also developed in response to lupin removal. The results of this study have implications for restoration projects in sand dunes. Pest management alone is unlikely to be sufficient to restore plant communities. Given the difficulties in restoring plant communities once an invasive species has established, managers should prioritize actions to prevent the spread of invasive species into uninvaded areas of sand dunes. Finally, the response to lupin invasion and removal differed between dune habitats. This highlights the importance of tailoring a pest management program to restoration goals by, for example, prioritizing areas in which the impacts of the invading species are greatest.

Reintroduction of locally extinct vertebrates impacts arid soil fungal communities.

Introduced species have contributed to extinction of native vertebrates in many parts of the world. Changes to vertebrate assemblages are also likely to alter microbial communities through coextinction of some taxa and the introduction of others. Many attempts to restore degraded habitats involve removal of exotic vertebrates (livestock and feral animals) and reintroduction of locally extinct species, but the impact of such reintroductions on microbial communities is largely unknown. We used high-throughput DNA sequencing of the fungal internal transcribed spacer I (ITS1) region to examine whether replacing exotic vertebrates with reintroduced native vertebrates led to changes in soil fungal communities at a reserve in arid central Australia. Soil fungal diversity was significantly different between dune and swale (interdune) habitats. Fungal communities also differed significantly between sites with exotic or reintroduced native vertebrates after controlling for the effect of habitat. Several fungal operational taxonomic units (OTUs) found exclusively inside the reserve were present in scats from reintroduced native vertebrates, providing a direct link between the vertebrate assemblage and soil microbial communities. Our results show that changes to vertebrate assemblages through local extinctions and the invasion of exotic species can alter soil fungal communities. If local extinction of one or several species results in the coextinction of microbial taxa, the full complement of ecological interactions may never be restored.

Responses of Dune Plant Communities to Continental Uplift from a Major Earthquake: Sudden Releases from Coastal Squeeze

Vegetated dunes are recognized as important natural barriers that shelter inland ecosystems and coastlines suffering daily erosive impacts of the sea and extreme events, such as tsunamis. However, societal responses to erosion and shoreline retreat often result in man-made coastal defence structures that cover part of the intertidal and upper shore zones causing coastal squeeze and habitat loss, especially for upper shore biota, such as dune plants. Coseismic uplift of up to 2.0 m on the Peninsula de Arauco (South central Chile, ca. 37.5º S) caused by the 2010 Maule earthquake drastically modified the coastal landscape, including major increases in the width of uplifted beaches and the immediate conversion of mid to low sandy intertidal habitat to supralittoral sandy habitat above the reach of average tides and waves. To investigate the early stage responses in species richness, cover and across-shore distribution of the hitherto absent dune plants, we surveyed two formerly intertidal armoured sites and a nearby intertidal unarmoured site on a sandy beach located on the uplifted coast of Llico (Peninsula de Arauco) over two years. Almost 2 years after the 2010 earthquake, dune plants began to recruit, then rapidly grew and produced dune hummocks in the new upper beach habitats created by uplift at the three sites. Initial vegetation responses were very similar among sites. However, over the course of the study, the emerging vegetated dunes of the armoured sites suffered a slowdown in the development of the spatial distribution process, and remained impoverished in species richness and cover compared to the unarmoured site. Our results suggest that when released from the effects of coastal squeeze, vegetated dunes can recover without restoration actions. However, subsequent human activities and management of newly created beach and dune habitats can significantly alter the trajectory of vegetated dune development. Management that integrates the effects of natural and human induced disturbances, and promotes the development of dune vegetation as natural barriers can provide societal and conservation benefits in coastal ecosystems.

Growth, photosynthesis and stress-inducible genes of Phragmites australis (Cav.) Trin. ex Steudel from different habitats

The present study investigates growth of Phragmites australis in relation to photosynthesis and stress-inducible genes in its natural habitats. P. australis was collected from fresh water (FW), brackish water (BW), mesophytic (M), salt marsh (SM) and sand dune (SD) habitats. These habitats were categorized according to their soil properties. FW and BW habitats are mainly characterized by flooded soil (hypoxia). SM and SD habitats are typical habitats for salt and drought conditions. Shoot growth parameters estimated in the present study would indicate that the optimum growth was in M habitat. The growth in other habitats was lower than that in M one and this reduction coincided with a reduction in photosynthetic rate (A). Internal CO2 concentration (Ci) did not show any significant reduction in all studied habitats except in M one. Starch, total soluble sugars and Rubisco contents could suggest that the growth reduction in FW habitat was a consequence of the reduction in photosynthetic rate while the reduction in growth was a cause of photosynthetic inhibition in BW habitat. Alcohol dehydrogenase (ADH) transcript level was constitutively expressed, and it was significantly increased in leaves collected from BW and SD habitats, suggesting its involvement in the fermentative metabolism. The expression of leaf plasma membrane Na+/H+ antiporter (SOS1) and high affinity potassium uptake (HKT) were stimulated in SM leaves assuming their roles in Na+ re-circulation and K+ uptake to maintain K+/Na+ ratio higher than one inside the leaf. Moreover, the reduced leaf water content could play a role in ion homeostasis inside this species. P. australis had the ability to maintain a stable water use efficiency (WUE) in all studied habitats assuming its ability in economizing water and maintaining the assimilation rate.

Seasonal habitat preference by the flagship species Testudo hermanni: Implications for the conservation of coastal dunes

In this study, we explored if, how, and when the European Union habitats (EU sensu Habitats Directive 92/43/CEE) are used by the flagship species Testudo hermanni in a well-preserved coastal dune system of the Italian peninsula. Radio telemetry data and fine-scale vegetation habitat mapping were used to address the following questions: (a) is each EU habitat used differentially by Hermann's tortoises? (b) is there any seasonal variation in this utilization pattern? (c) how does each habitat contribute to the ecological requirements of the tortoises? Nine tortoises were fitted with transmitters and monitored for the entire season of activity. The eight EU habitats present in the study area were surveyed and mapped using GIS. The seasonal preferential use or avoidance of each habitat was tested by comparing, through bootstrap tests, the proportion of habitat occupied (piTh) with the proportion of available habitat in the entire landscape (piL). The analysis of 340 spatial locations showed a marked preference for the Cisto-Lavanduletalia dune sclerophyllous scrubs (EU code 2260) and a seasonal selection of Juniperus macrocarpa bushes (EU code 2250*), wooded dunes with Pinus (EU code 2270) and mosaic of dune grasslands and sclerophyllous scrubs (EU codes 2230, 2240, 2260). Seasonal variation of habitat preference was interpreted in light of the different feeding, thermoregulation and reproductive needs of the tortoises. Our results stress the ecological value of EU coastal dune habitats and suggest prioritization of conservation efforts in these ecosystems.

Proposal for new EU habitats associated with coastal dune fields of the Macaronesian region. A case study in the Canary Islands (Spain)

The aim of this work is to identify habitats of European interest for the existing dunes in the Canaries, in order to provide data for their proper management. Dune systems considered were the following: aeolian sedimentary systems that cover both most of the island of La Graciosa and also the dune fields of Maspalomas (Gran Canaria) and Corralejo (Fuerteventura). The methodology consisted of overlapping layers of habitats and vegetation by using geographic information systems, so the correspondence between habitat and plant community are analyzed. The results indicate that dune habitats in the Canary Islands have not been well defined. The habitat “2110 embryonic shifting dunes” is associated with several situations incompatible with their biotic and abiotic characteristics. Meanwhile, habitat “2130 fixed dunes with herbaceous vegetation (grey dunes)” is linked, among others, to the phytosociological association Traganetum moquinii. However, embryonic dune formation in the Canaries is mainly done by this community, which is inconsistent with its inclusion in the grey dunes habitat. The proposed habitats of European interest associated with dunes in the Canaries are the following: Coastal shifting dunes with Traganum moquinii, dunes with Tamarix canariensis, Macaronesian aeolian sand sheets and humid dune slacks. It is also suggested the need for a comprehensive study of dune habitats existing in the Canaries and Macaronesia, covering the whole of aeolian sedimentary systems, performing a proper identification, characterization and detailed mapping of these habitats, based on both the existing vegetation and also on the associated landforms and geomorphic processes.

Fungal symbiosis and precipitation alter traits and dune building by the ecosystem engineer, Ammophila breviligulata.

Ecosystem engineer species influence their community and ecosystem by creating or altering the physical structure of habitats. The function of ecosystem engineers is variable and can depend on both abiotic and biotic factors. Here we make use of a primary successional system to evaluate the direct and interactive effects of climate change (precipitation) and fungal endophyte symbiosis on population traits and ecosystem function of the ecosystem engineering grass species, Ammophila breviligulata. We manipulated endophyte presence in A. breviligulata in combination with rain-out shelters and rainfall additions in a factorial field experiment established in 2010 on Lake Michigan sand dunes. We monitored plant traits, survival, growth, and sexual reproduction of A. breviligulata from 2010-2013, and quantified ecosystem engineering as the sand accumulation rate. Presence of the endophyte in A. breviligulata increased vegetative growth by up to 19%, and reduced sexual reproduction by up to 46% across all precipitation treatments. Precipitation was a less significant factor than endophyte colonization for A. breviligulata growth. Reduced precipitation increased average leaf number per tiller but had no other effects on plant traits. Changes in A. breviligulata traits corresponded to increases in sand accumulation in plots with the endophyte as well as in plots with reduced precipitation. Sand accumulation is a key ecosystem function in these primary successional habitats, and so microbial symbiosis in this ecosystem engineer could lead to direct effects on the value of these dune habitats for humans.

The role of natural vegetation in the analysis of the spatio-temporal changes of coastal dune system: a case study in Sicily

The coastal dunes of the Mediterranean area are among the most vulnerable and seriously threatened ecosystems due to human activities. Habitat fragmentation is generally considered as one of the most influential factors in biodiversity loss. In this paper, we investigated the temporal and spatial changes in the floristic composition and abundance in sand dunes along a coastal strip of Sicily (Italy). Six transects perpendicular to the coastal line were selected in southern Sicily. For each transect, the floristic composition and cover of the species were determined using standard releve methods. A total of 186 plots were collected. The plots data was analyzed using classification (UPGMA, Chord coefficient) and ordination methods (Detrended Correspondence Analysis). A total of 14 plant communities with specific floristic composition were established, belonging mainly to six habitats. To evaluate the reduction of the habitats of the complex dune system in the last 70 years, aerial photos from 1938 to 2007 have been used and elaborated with ArcGis 10.3. The cartographic analysis shows a radical transformation of the Macconi dune system with a reduction of the dune habitats. In particular, the results show a strong reduction/loss of habitats (2250, 2210 and 2120 EU code) as well as a strong alteration of the ecological succession of the psammophilous vegetation. Moreover, floristic richness and diversity index showed an increased trend from the coastal line towards inner dunal zone.

‘Building with nature’ at the Dutch dune coast: compensation target management in Spanjaards Duin at EU and regional policy levels

A new dune area was constructed using beach and foreshore nourishment along the Dutch dune coast in the delta area. The new area is intended as a compensation for losses of existing high quality dune habitat as a result of the use of Maasvlakte 2 (MV-2), the new extension of Rotterdam harbour. Compensation was required under international EU Community regulations because the existing dune areas that could potentially be affected are protected under the EU Natura2000. The paper discusses the political and management aspects at EU- and regional levels. In The Netherlands, the construction of a compensation area along the coast, due to the extension of an international harbour, has been a procedure without precedence. The knowledge-based design and construction of the area and the set up of monitoring and evaluation programs in the context of policy and management are described. We believe that they provide innovative ideas for coastal management worldwide. Aspects of construction and landscape ecological developments of the same area have been reported in an earlier paper (van der Meulen et al. 2014).

Positive Species Interactions as Drivers of Vegetation Change on a Barrier Island

Monge, J.A. and Gornish, E.S., 2015. Positive species interactions as drivers of vegetation change on a barrier island.Positive species interactions have been shown to occur in a variety of plant systems, and the importance of these interactions is expected to vary with resource availability and abiotic stress. The processes by which these types of relationships operate and influence plant communities in coastal environments, however, are not fully understood. Positive species interactions were observed in areas of St. George Island, Florida, shortly after transplanting dune species for a restoration experiment designed to encourage the growth of foredune, interdune, and backdune vegetation. The dune habitats in St. George are subject to abiotic stresses that vary in type and magnitude, and the environmental factors responsible for ameliorating these conditions and encouraging positive vegetation change operate differently across these areas. We (1) investigated if transplants encouraged positive changes in vegetation across dune habitats, (2) determined whether disturbance (through transplanting) played a role, and (3) tested environmental factors involved in positive interactions to explain the changes in vegetation observed across dune habitats. The presence of transplants positively modified vegetation (e.g., species richness or cover) across all dune habitats. Experimental disturbance had no strong overall positive effect on vegetation change. Shading and soil moisture redistribution had differential effects on vegetation change among habitats, suggesting that these environmental factors interact with the abiotic characteristics unique to each dune habitat in complex ways. Our results suggest that experimentation over a longer time scale might be required to fully understand the extent at which positive interactions affect vegetation patterns along stressful environmental gradients.

Changes in plant species composition of coastal dune habitats over a 20-year period.

Coastal sandy ecosystems are increasingly being threatened by human pressure, causing loss of biodiversity, habitat degradation and landscape modifications. However, there are still very few detailed studies focussing on compositional changes in coastal dune plant communities over time. In this work, we investigated how coastal dune European Union (EU) habitats (from pioneer annual beach communities to Mediterranean scrubs on the landward fixed dunes) have changed during the last 20 years. Using phytosociological relevés conducted in 1989-90 and in 2010-12, we investigated changes in floristic composition over time. We then compared plant cover and the proportion of ruderal, alien and habitat diagnostic species ('focal species') in the two periods. Finally, we used Ellenberg indicator values to define the 'preferences' of the plant species for temperature and moisture. We found that only fore dune habitats showed significant differences in species cover between the two time periods, with higher plant cover in the more recent relevés and a significant increase in thermophilic species. Although previous studies have demonstrated consistent habitat loss in this area, we observed that all coastal dune plant communities remain well represented, after a 20-year period. However, fore dunes have been experiencing significant compositional changes. Although we cannot confirm whether the observed changes are strictly related to climatic changes, to human pressure or to both, we hypothesize that a moderate increment in average yearly temperature may have promoted the increase in plant cover and the spread of thermophilic species. Thus, even though human activities are major driving forces of change in coastal dune vegetation, at the community scale climatic factors may also play important roles. Our study draws on re-visitation studies which appear to constitute a powerful tool for the assessment of the conservation status of EU habitats.

Effects of disturbance on vegetation by sand accretion and erosion across coastal dune habitats on a barrier island.

Coastal geomorphology and vegetation are expected to be particularly sensitive to climate change, because of disturbances caused by sea-level rise and increased storm frequency. Dunes have critical reciprocal interactions with vegetation; dunes create habitats for plants, while plants help to build dunes and promote geomorphological stability. These interactions are also greatly affected by disturbances associated with sand movement, either in accretion (dune building) or in erosion. The magnitude and intensity of disturbances are expected to vary with habitat, from the more exposed and less stable foredunes, to low-lying and flood-prone interdunes, to the protected and older backdunes. Permanent plots were established at three different spatial scales on St George Island, FL, USA, where the vegetation and dune elevation were quantified annually from 2011 to 2013. Change in elevation, either through accretion or erosion, was used as a measure of year-to-year disturbance over the 2 years of the study. At the scale of different dune habitats, foredunes were found to have the greatest disturbance, while interdunes had the least. Elevation and habitat (i.e. foredune, interdune, backdune) were significantly correlated with plant community composition. Generalized linear models conducted within each habitat show that the change in elevation (disturbance) is also significantly correlated with the plant community, but only within foredunes and interdunes. The importance of disturbance in exposed foredunes was expected and was found to be related to an increasing abundance of a dominant species (Uniola paniculata) in eroding areas. The significant effect of disturbance in the relatively stable interdunes was surprising, and may be due to the importance of flooding associated with small changes in elevation in these low-lying areas. Overall, this study documents changes in the plant community associated with elevation, and demonstrates that the foredune and interdune communities are also associated with the responses of specific species to local changes in elevation due to accretion or erosion.

Changes in the chlorophyll a and b content in different-aged leaves of Spergula vernalis Willd.

The result are reported of investigations on the seasonal variations in the chlorophyll a and b content in the successive leaf tiers of <i>Spergula vernalis</i> Willd. growing in two different dune habitats. It was endeavoured to determine the influence of habitat conditions on the concentration of green pigments. The eventual relationship between their amount and the production of organic matter by the plants is discussed.

Role of Na+ manipulating genes in Phragmites australis adaptation to different habitats

Phragmites australis adapts to different habitats and tolerate drought and/or salt stress. In the present study, P. australis was collected from mesophytic, brackish water, sand dune, fresh water and salt marsh habitats. The leaf fresh weight was optimum in mesophytic habitats and it was negatively affected by stress found in other habitats. Water content followed the same trend for the fresh weight. The decrease in water content could be a tolerance strategy. Na + content was higher in roots than in leaves for all habitats. In contrast, K + content was higher in leaves than in roots. K + /Na + ratio was higher than unity in leaves for all habitats even within roots collected from salt marsh. Except for leaves collected from mesophytic habitats, K + /Na + ratio was less than one (1.1). NHX1 expression level was higher in roots than that in leaves suggesting that this plant may accumulate Na + inside root vacuoles to restrict its movement to shoot. However, the transcript level of SOS1 was not detected in any root collected from different habitats. Therefore, this reed may have other mechanisms for Na + extrusion. However, SOS1 transcript level was detected in leaves collected from different habitats suggesting that SOS1 could play different roles in P. australis tolerance.

Regional metacommunities in two coastal systems: spatial structure and drivers of plant assemblages

AbstractAimBiogeographical patterns in metacommunities are still poorly understood, and different processes are expected to occur in different habitats. We analysed the regional plant metacommunities of coastal habitats to test whether (1) the influence of space and climate differs between two habitats differentiated along the seashore–inland gradient, and (2) regional variation in species composition of these habitats can be ascribed to different metacommunity paradigms.LocationThe entire coast of the Iberian Peninsula, south‐western Europe.MethodsWe collected data on the plant species composition of coastal sites on sand dunes across 3000 km of coastline. The sites were classified into two habitats corresponding to shifting and stable sand dunes, and divided into three distinct geographical regions: Cantabrian, Atlantic and Mediterranean. We assessed the geographical structure of the species composition using ordination, estimates of species turnover and spatial autocorrelation. We then used multivariate models and variation partitioning to test the influence of climatic and spatial effects. Analyses were conducted for the whole data set and the geographical subsets.ResultsMetacommunities from shifting and stable dunes showed similar spatial patterns, with the highest species turnover occurring in the Mediterranean region. Similarities between communities that were nearer each other (typically < 100 km) were weaker in shifting than in stable dunes, although the distance decay for sites that were further apart was similar in both habitats. Variation in species composition in shifting dunes was mainly explained by distance and climate, while in stable dunes the effect of climate was clearly dominant. The observed differences were relatively consistent across geographical regions.Main conclusionsDistinct processes structure the metacommunities in two dune habitats differentiated along the seashore–inland gradient. Communities of shifting dunes seem to be structured by an interplay of neutral or patch‐dynamic processes and to a lesser degree by species sorting. In contrast, communities of stable dunes are mainly governed by species sorting in response to climatic gradients. These results highlight the importance of differentiating habitats according to local ecological factors when analysing regional patterns in metacommunities.

Seabird Colonies of the Small Islands of Bahía Santa María-La Reforma, Sinaloa, México

Abstract. During the 2010–2011 and 2011–2012 breeding seasons (November to June), there were 21 colonies of 13 species, with at least 40,000 to 50,000 pairs of seabirds on six islands of Bahia Santa Maria-La Reforma in Mexico. Bahia Santa Maria maintains the largest breeding congregation of the west coast of Mexico for Laughing Gull (Leucophaeus atricilla; 22,000 pairs), Royal Tern (Thalasseus maximus; 11,000 pairs) and Black Skimmer (Rynchops niger; 1,500 pairs). In the past decade, most of the species that breed on El Rancho Island (coastal dune habitat) have increased their population size, apparently related to a combination of factors such as colonies recently established (and hence still expanding) and increased habitat availability. On the other hand, species breeding on islands with mangroves seem to be decreasing (in particular the Brown Pelican (Pelecanus occidentalis) population), but with no obvious reason to explain these low numbers of some species. Despite the small size of the islands used...

Effects of seabird nitrogen input on biomass and carbon accumulation after 50 years of primary succession on a young volcanic island, Surtsey

Abstract. What happens during primary succession after the first colonizers have occupied a pristine surface largely depends on how they ameliorate living conditions for other species. For vascular plants the onset of soil development and associated increase in nutrient (mainly nitrogen; N) and water availability is especially important. Here, we report the relationship between N accumulation and biomass and ecosystem carbon (C) stocks in a 50-year-old volcanic island, Surtsey, Iceland, where N stocks are still exceptionally low. However, a 28-year-old seagull colony on the island provided nutrient-enriched areas, which enabled us to assess the relationship between N stock and biomass and ecosystem C stocks across a much larger range in N stock. Further, we compared areas on shallow and deep tephra sands as we expected that deep-rooted systems would be more efficient in retaining N. The sparsely vegetated area outside the colony had accumulated 0.7 kg N ha−1 yr−1, which was ca. 50–60% of the estimated N input rate from wet deposition. This approximates values for systems under low N input and bare dune habitats. The seagulls have added, on average, 47 kg N ha−1 yr−1, which induced a shift from belowground to aboveground in ecosystem N and C stocks and doubled the ecosystem N-use efficiency, determined as the ratio of biomass and C storage per unit N input. Soil depth did not significantly affect total N stocks, which suggests a high N retention potential. Both total ecosystem biomass and C stocks were strongly correlated with N stock inside the colony, which indicated the important role of N during the first steps of primary succession. Inside the colony, the ecosystem biomass C stocks (17–27 ton C ha−1) had reached normal values for grasslands, while the soil organic carbon (SOC) stocks (4–10 ton C ha−1 were only a fraction of normal grassland values. Thus, it will take a long time until the SOC stock reaches equilibrium with the current primary production, during which conditions for new colonists may change.

Alien plants of coastal dune habitats in southern Spain

Alien plants from psammophilous ecosystems have been studied in southern Spain. Sixteen sites, which are included in the Andalusian Network of Protected Spaces, have been chosen along 1100 km of Andalusian coasts in order to verify the degree of abundance and influence of these species on different communities. Out of the 26 localized species, the increase of some invasive plants, such as Arctotheca calendula, Agave americana, A. sisalana, Cortaderia selloana, Lantana camara and Opuntia dillenii, affects the conservation of some natural coastal ecosystems.