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.     

Understanding the influence of urbanization on invasibility: <Emphasis Type="Italic">Carpobrotus edulis</Emphasis> as an exemplar

Coastal dune areas are valuable ecosystems, generally impacted by habitat destruction and invasive alien species. In this study, we assessed how human disturbance and invasion by Carpobrotus edulis impact the soils and the establishment of native flora in the north-western coastal regions of Spain. We compared soil characteristics (pH, conductivity, water content, nutrients and enzymatic activities) and native plant as well as C. edulis fitness correlates (germination and early growth) between uninvaded and invaded soils from urban and natural coastal dune areas. We found that human disturbance impacts coastal soils by increasing organic matter and water content, modifying soil nutrients and cycles, and reducing the pH in urban soils. The presence of invasive C. edulis further increases these impacts. These changes in soil characteristics allow for the establishment of the native, but ruderal, Scolymus hispanicus and non-native C. edulis, both of which are not adapted to the typically limiting conditions of coastal dunes. In some instances, the coastal dune endemic, Malcolmia littorea, showed no fitness effects in response to urbanization or the presence of C. edulis. These results suggest that human disturbed coastal areas might be more easily invaded than natural areas. More broadly, our findings of differential responses of different native species to disturbance and invasion, illustrate the need for multi-taxon approaches when assessing the impacts of invasive species.     

Soil type affects seedling shade response at low light for two Inga species from Costa Rica

Distributions of many humid tropical tree species are associated with specific soil types. This specificity most likely results from processes at the seedling stage, but light rather than nutrient levels is generally considered the dominant limitation for seedling growth in the tropical forest understory. If nutrients are limiting and allocation to belowground resources differs, seedling growth responses to shade should also differ. Here we tested the effects of soil type and light environment on the seedling growth of two canopy tree species in the genus Inga with different soil-type and light-environment affinities as adults. Inga alba is a shade-tolerant soil generalist and I. oestediana is a light-demanding soil specialist. We used four native soils and three light levels (1 and 5% of full sun in shade houses and the forest understory). All growth variables were greatest in 5% full sun, with highest growth rates for the light-demanding soil-type specialist. Soil type significantly affected growth parameters, even at the lower light levels. The specialist grew best on the soils with the most soil phosphorus where adult trees typically occur. Leaf tissue nitrogen:phosphorus ratios suggest increased phosphorus limitation in the low phosphorus soils and with increased light level. Light and soil interacted to significantly affect seedling biomass allocation, growth, and net assimilation rates, indicating that the seedling shade responses were affected by soil type. Seedlings growing on high nutrient soil allocated less to roots and more to photosynthetic tissue. Adult distributions of these two Inga species may be a result of the different growth rates of seedlings in response to the interactive effects of light and soil.     

科尔沁沙地封育恢复过程中植物群落特征变化及影响因素

封育是退化沙地植被恢复与生态重建的重要措施, 理解长期处于封育状态下不同类型沙地植物群落特征变化及其影响因素有利于沙地植被恢复和生态重建。该文基于对科尔沁沙地长期封育的流动沙丘(2005年封育)、固定沙丘(1985年封育)和沙质草地(1997年封育)连续多年(2005-2017年)的植物群落调查, 结合土壤种子库、土壤养分以及气象数据, 分析了植物群落特征变化及其对环境变化的响应。研究结果表明流动沙丘植被盖度显著增加, 群落生物量和物种多样性年际间波动变化, 但无明显趋势; 固定沙丘植物群落存在逆行演替趋势, 具体表现为群落生物量、灌木和半灌木以及豆科优势度显著下降, 而一年生和多年生杂类草优势度显著增加; 沙质草地群落物种丰富度和多年生禾草优势度存在降低趋势, 并且一年生杂类草优势度明显高于其他功能群, 群落存在退化现象。3类沙地土壤种子密度变化不显著, 而种子丰富度在流动沙丘显著增加, 在固定沙丘和沙质草地有下降趋势, 土壤养分仅有有效氮和有效磷含量增加。回归分析结果表明气温和降水是影响年内生物量积累的主要因素, 但对年际间群落生物量和物种丰富度变化影响不大。除趋势对应分析结果显示土壤种子库与植物群落之间存在很高的相似性, 典型相关分析结果表明沙质草地植物群落与土壤养分紧密相关, 而固定沙丘群落主要与土壤水分紧密相关。综合以上结果可知, 封育33年的固定沙丘群落和封育21年的沙质草地群落都存在退化现象, 而封育11年的流动沙丘群落正在缓慢恢复, 因此封育年限的设定对退化沙地植被恢复至关重要, 封育时间过长不仅不利于植物群落恢复, 反而会使群落发生逆行演替, 建议封育年限的设定应综合考虑植被退化程度、土壤养分状况、土壤种子库基础以及气候条件等因素的影响。     

Adventitious root production and plastic resource allocation to biomass determine burial tolerance in woody plants from central Canadian coastal dunes

BACKGROUND AND AIMS: Burial is a recurrent stress imposed upon plants of coastal dunes. Woody plants are buried on open coastal dunes and in forested areas behind active blowouts; however, little is known about the burial responses and adaptive traits of these species. The objectives of this study were: (a) to determine the growth and morphological responses to burial in sand of seven woody plant species native to central Canadian coastal dunes; and (b) to identify traits that determine burial tolerance in these species. METHODS: Field experiments were conducted to determine the responses of each species to burial. Saplings were exposed to burial treatments of 0, 10, 25, 50 and 75 % of their height. Burial responses were evaluated based on regressions of total biomass, height, adventitious root production and percentage allocation to shoot, root and adventitious root biomass on percentage burial. KEY RESULTS: Pinus strobus and Picea glauca lacked burial tolerance. In response to the burial gradient, these species showed a strong linear decline in total biomass, minimal adventitious root production that peaked at moderate levels (25-50 % burial) and no change in allocation to shoots vs. roots. The tolerant species Juniperus virginiana, Thuja occidentalis and Picea mariana showed a quadratic response to burial, with little change in biomass up to 50 % burial, but a large decline at 75 %. These species produced abundant adventitious roots up to 50 % burial, but did not alter allocation patterns over the range of burial levels. Populus balsamifera and Salix cordata were stimulated by burial. These species showed linear increases in biomass with increasing burial, produced copious adventitious roots across the gradient and showed a clear shift in allocation to vertical shoot growth and adventitious root production at the expense of the original roots under high burial conditions. CONCLUSIONS: Adventitious root production and plastic resource allocation to biomass are adaptive traits of coastal dune woody plants in central Canada, and provide a basis for assessing burial tolerance in woody plants on coastal dunes throughout the world.     

Interactions between resources and abiotic conditions control plant performance on subarctic coastal dunes

Both abiotic conditions and resource levels affect the performance of plants on coastal dune systems. On the foredune, environmental factors are particularly limiting for plant growth and these vary along a short topographical gradient, from the foot to the ridge. On subarctic coastal dunes in northeastern Canada, this topographical gradient is paralleled by a plant sequence that typically involves Honckenya peploides, Elymus mollis, and Lathyrus japonicus. In this study, field nutrient additions were carried out to evaluate the importance of N and/or P limitation on foredune plant performance. Also, glasshouse experiments were done to determine the significance of interactions between substrate resources (i.e., nutrients and water), and between substrate resources (i.e., nutrients) and an abiotic condition (i.e., salt spray) on the growth of a dune species. Field nutrient additions did not result in any significant increase in plant biomass, although nutrients were accumulated in the rhizomes of all three species present on the foredune and in the aboveground tissues of Elymus. Glasshouse experiments on Elymus showed that nutrient addition could increase plant biomass. However, water availability and salt spray interfered with nutrient use by the plants. I suggest that such interactions between resources and abiotic conditions may significantly affect plant performance and plant sequence on the foredune of coastal dune systems.     

Ecological Assessment of Dune Restorations in the Great Lakes Region

Because of the economic and environmental importance of stabilizing fragile sand dune habitats, restoration of dunes has become a common practice. Restoration efforts in the Great Lakes and East Coast regions of North America often consist of planting monocultures of the dominant native grass species, Ammophila breviligulata. We evaluated 18 dune restoration projects in the Great Lakes region conducted over the past 25 years. We characterized attributes of diversity (plants and insects), vegetation structure (plant biomass and cover), and ecological processes (soil nutrients and mycorrhizal fungi abundance) in each restoration, and we compared these measures to geographically paired natural dune communities. Restoration sites were similar to reference sites in most measured variables. Differences between restorations and reference sites were mostly explained by differences in ages, with the younger sites supporting slightly lower plant diversity and mycorrhizal spore abundance than older sites. Plant community composition varied little between restored and reference sites, with only one native forb species, Artemisia campestris, occurring significantly more often in reference sites than restored sites. Although it remains unclear whether more diverse restoration plantings could accelerate convergence on the ecological conditions of reference dunes, in general, traditional restoration efforts involving monoculture plantings of A. breviligulata in Great Lakes sand dunes appear to achieve ecological conditions found in reference dunes.     

Comparative analysis of the contribution of phytochelatins to cadmium and arsenic tolerance in soybean and white lupin

The biosynthesis of phytochelatins (PCs) plays a crucial role in the detoxification and homeostasis of heavy metals and metalloids in plants. However, in an increasing number of plant species metal(loid) tolerance is not well correlated with the accumulation of PCs: tolerant ecotypes frequently contain lower levels of PCs than non-tolerant ecotypes. In this study we have compared the responses of soybean (Glycine max L. cv. Resnik) and white lupin (Lupinus albus L. cv. Marta) to cadmium and arsenate in order to assess the role of homophytochelatins (hPCs) in the tolerance of soybean to these toxic elements. Soybean plants treated with Cd and As showed a high contribution of homo-glutathione (hGSH) to the pool of thiols in shoots in comparison to white lupin. Higher levels of hPCs in Cd-treated soybeans compared to PCs in lupins did not prevent growth inhibition. In contrast, the role of hPCs in the detoxification mechanism to arsenate in soybean seems to be clearer, showing higher thiol concentrations and lower growth reductions than those present in lupin plants.     

Native and exotic foundation grasses differ in traits and responses to belowground tri-trophic interactions

A plant’s growth and fitness are influenced by species interactions, including those belowground. In primary successional systems, belowground organisms are known to have particularly important control over plant growth. Exotic plant invasions in these and other habitats may in part be explained by altered associations with belowground organisms compared to native plants. We investigated the growth responses of two foundation grasses on Great Lakes sand dunes, the native grass Ammophila breviligulata and the exotic grass Leymus arenarius, to two groups of soil organisms with important roles in dune succession: arbuscular mycorrhizal fungi (AMF) and plant-parasitic nematodes (PPN). We manipulated the presence/absence of two generalist belowground species known to occur in Great Lakes dunes, Rhizophagus intraradices (AMF) and Pratylenchus penetrans (PPN) in a factorial greenhouse experiment and assessed the biomass production and root architectural traits of the plants. There were clear differences in growth and above- and belowground architecture between Ammophila and Leymus, with Leymus plants being bigger, taller, and having longer roots than Ammophila. Inoculation with Rhizophagus increased above- and belowground biomass production by ~32% for both plant species. Inoculation with Pratylenchus decreased aboveground biomass production by ~36% for both plant species. However belowground, the exotic Leymus was significantly more resistant to PPN than the native Ammophila, and gained more benefits from AMF in belowground tri-trophic interactions than Ammophila. Overall, our results indicate that differences in plant architecture coupled with altered belowground interactions with AMF and PPN have the potential to promote exotic plant invasion.     

Contrasting responses of native and alien plant species to soil properties shed new light on the invasion of dune systems

在陆地生态系统中，沿海沙丘特别容易受到外来植物的入侵。许多研究将沙丘生境的入侵归因于人为因素，但对土壤性质和植物性状在植物 入侵中的作用却知之甚少。本研究考察了沙丘系统土壤特征与外来植物入侵的关系，重点研究了土壤养分、土壤盐分和植物功能特征之间的相互作 用。研究地点是马拉诺和格拉多泻湖(北亚得里亚海)的沙质堰洲岛。根据沙丘系统生态梯度上的主要生境(前沙丘、后沙丘和盐沼)，在10 个区域内选择100个地块(4 m × 4 m)。在每个地块中记录所有植物物种的发生和丰度，并收集一个土壤核。对每个土壤样品进行土壤质地、电导率(代表土壤盐 分)、有机碳和氮含量分析，并与本地和外来植物的种类数和覆盖度相关联。分析外来和本地物种主要的生殖功能和营养功能性状在生境中的变化。研究结果表明，土壤性质对外来物种库和本地物种库的影响不同，与植物整体多样性密切相关。在后沙丘(最易入侵)的生境中，高的土壤导电性限制了外来物种的数量，但土壤有机碳含量随着外来植物丰度的增加而增加，这也表明植物入侵与土壤之间存在潜在的反馈过程。只有在后沙丘生境中，随着环境条件的改善和植物竞争的加剧，本地植物和外来植物的功能性状谱有显著的趋同。本研究结果表明，在恶劣条件下，只有本地特有植物才能茁壮成长，而在中等条件下，土壤特性梯度与植物特性协同作用，抑制/促进外来植物丰富度。     

Biomass reallocation and the mobilization of leaf resources support dune plant growth after sand burial

The stimulation of dune plant growth in response to burial is a vital attribute allowing survival in areas of mobile sand. Numerous resource-related and physiological mechanisms of growth stimulation have been suggested in the past, but few have been tested comparatively. Manipulation experiments using Scaevola plumieri, an important subtropical coastal dune forming species, demonstrated that physiological shifts were of great importance in determining the nature of the stimulation response to burial. The production of stem length and replacement of leaf area were stimulated by burial, whereas net mass production was similar between buried and unburied treatments. Remobilization of buried leaf resources, seasonal effects, and a shift in biomass allocation to stem production played the greatest role in the compensatory growth response. Other factors, such as increased soil nutrients, changes in photosynthesis, and changes in the costs of producing tissue were of less importance. Thus, the stimulated growth of species adapted to live on mobile dunes is explained by a number of resource-related and physiological mechanisms acting in concert.     

Shrubs as ecosystem engineers in a coastal dune: influences on plant populations,communities and ecosystems

Question: How do two shrubs with contrasting life‐history characteristics influence abundance of dominant plant taxa, species richness and aboveground biomass of grasses and forbs, litter accumulation, nitrogen pools and mineralization rates? How are these shrubs – and thus their effects on populations, communities and ecosystems – distributed spatially across the landscape? Location: Coastal hind‐dune system, Bodega Head, northern California. Methods: In each of 4 years, we compared vegetation, leaf litter and soil nitrogen under canopies of two native shrubs –Ericameria ericoides and the nitrogen‐fixing Lupinus chamissonis– with those in adjacent open dunes. Results: At the population level, density and cover of the native forb Claytonia perfoliata and the exotic grass Bromus diandrus were higher under shrubs than in shrub‐free areas, whereas they were lower under shrubs for the exotic grass Vulpia bromoides. In contrast, cover of three native moss species was highest under Ericameria and equally low under Lupinus and shrub‐free areas. At community level, species richness and aboveground biomass of herbaceous dicots was lower beneath shrubs, whereas no pattern emerged for grasses. At ecosystem level, areas beneath shrubs accumulated more leaf litter and had larger pools of soil ammonium and nitrate. Rates of nitrate mineralization were higher under Lupinus, followed by Ericameria and then open dune. At landscape level, the two shrubs – and their distinctive vegetation and soils – frequently had uniform spatial distributions, and the distance separating neighbouring shrubs increased as their combined sizes increased. Conclusions: Collectively, these data suggest that both shrubs serve as ecosystem engineers in this coastal dune, having influences at multiple levels of biological organization. Our data also suggest that intraspecific competition influenced the spatial distributions of these shrubs and thus altered the distribution of their effects throughout the landscape.     

Fine roots of <Emphasis Type="Italic">Prosopis flexuosa</Emphasis> trees in the field. Plant and soil variables that control their growth and depth distribution

Fine root growth in natural vegetation is difficult to predict due to its regulation by soil and plant factors. Field studies in arid ecosystems show a variety of root responses to soil resources and to plant aboveground phenology that sometimes differ from root responses predicted by controlled experiments. There is a pressing need to cover a greater diversity of plant species and ecological scenarios in field studies. In this paper, we have studied fine roots of Prosopis flexuosa trees living with or without access to phreatic water in an inter-dune valley and a dune flank, respectively, in the Central Monte Desert, Argentina. We have described fine root growth over time and at different depths by rhizotron observations and soil core auger samples in relation to soil water and nutrients, tree crown phenology, plant water and nutrient status. We have found that surface soil moisture from rainfall is the variable that best predicts seasonal topsoil fine root growth. Access to groundwater advanced leaf sprouting with respect to rainfall, but did not advance root growth that stayed linked to rainfall in valley and dune flank trees. Trees without access to phreatic water produced deeper and thicker or denser roots, which is consistent with the poor soil resource content of dunes. Variations in rainfall dynamics due to global climate change may have a particular impact on fine roots and ecosystem processes such as biogeochemistry and carbon budget in dune flank trees as well as in valley trees.     

Competition strength of two significant invasive species in coastal dunes

To investigate the effect of increased nutrient availability on competition amongst invasive and native plants, I measured changes in above and below ground biomass of Chrysanthemoides monilifera spp. rotundata (bitou bush) and Asparagus aethiopicus (asparagus fern) competing with two native species, Banksia integrifolia and Ficinia nodosa, under high- and low-nutrient regimes. Bitou bush, as a primary invader, was competitive under all conditions lowering the growth of native species in both high and low nutrients. Asparagus fern as a secondary invader, did not influence growth of native species but responded, like bitou bush, to high nutrients. Native species were generally negatively affected by increases in nutrients. With bitou bush soils often providing higher nutrients, the chance of secondary invasion by asparagus fern is more likely, although asparagus fern is unlikely to invade low nutrient soils quickly. The invasive species, therefore, differed in their competitive ability in these coastal dune communities.     

Phosphorus benefits of different legume crops to subsequent wheat grown in different soils of Western Australia

Certain legume crops, including white lupin (Lupinus albus L.), mobilise soil-bound phosphorus (P) through root exudates. The changes in the rhizosphere enhance P availability to these crops, and possibly to subsequent crops growing in the same soil. We conducted a pot experiment to compare phosphorus acquisition of three legume species with that of wheat, and to determine whether the legume crops influence growth and P uptake of a subsequent wheat crop. Field pea (Pisum sativum L.), faba bean (Vicia faba L.), white lupin (Lupinus albus L.) and wheat (Triticum aestivum L.) were grown in three different soils to which we added no or 20 mg P kg^–1 soil (P0, P20). Growth, P content and rhizosphere carboxylates varied significantly amongst crops, soils and P levels. Total P content of the plants was increased with applied phosphorus. Phosphorus content of faba bean was 3.9 and 8.8 mg/pot, at P0 and P20, respectively, which was about double that of all other species at the respective P levels. Field pea and white lupin had large amounts of rhizosphere carboxylates, whereas wheat and faba bean had negligible amounts in all three soils at both P levels. Wheat grew better after legumes than after wheat in all three soils. The effect of the previous plant species was greater when these previous species had received P fertiliser. All the legumes increased plant biomass of subsequent wheat significantly over the unplanted pots in all the soils. Faba bean was unparalleled in promoting subsequent wheat growth on all fertilised soils. This experiment clearly demonstrated a residual benefit of the legume crops on the growth of the subsequent wheat crop due to enhanced P uptake. Faba bean appeared to be a suitable P-mobilising legume crop plant for use in rotations with wheat.     

Does salt stress constrain spatial distribution of dune building grasses Ammophila arenaria and Elytrichia juncea on the beach?

Rising sea levels threaten coastal safety by increasing the risk of flooding. Coastal dunes provide a natural form of coastal protection. Understanding drivers that constrain early development of dunes is necessary to assess whether dune development may keep pace with sea‐level rise. In this study, we explored to what extent salt stress experienced by dune building plant species constrains their spatial distribution at the Dutch sandy coast. We conducted a field transplantation experiment and a glasshouse experiment with two dune building grasses Ammophila arenaria and Elytrigia juncea. In the field, we measured salinity and monitored growth of transplanted grasses in four vegetation zones: (I) nonvegetated beach, (II) E. juncea occurring, (III) both species co‐occurring, and (IV) A. arenaria dominant. In the glasshouse, we subjected the two species to six soil salinity treatments, with and without salt spray. We monitored biomass, photosynthesis, leaf sodium, and nutrient concentrations over a growing season. The vegetation zones were weakly associated with summer soil salinity; zone I and II were significantly more saline than zones III and IV. Ammophila arenaria performed equally (zone II) or better (zones III, IV) than E. juncea, suggesting soil salinity did not limit species performance. Both species showed severe winter mortality. In the glasshouse, A. arenaria biomass decreased linearly with soil salinity, presumably as a result of osmotic stress. Elytrigia juncea showed a nonlinear response to soil salinity with an optimum at 0.75% soil salinity. Our findings suggest that soil salinity stress either takes place in winter, or that development of vegetated dunes is less sensitive to soil salinity than hitherto expected.     

The role of the expansion of native-invasive plant species in coastal dunes: The case of Retama monosperma in SW Spain

Invasion by allochthonous plant species are identified, at present, among the main conservation hazards to coastal dunes. Nevertheless, the role of the expansion, with invasive character, of native species in these ecosystems has received little attention in ecological studies. In recent decades, Retama monosperma, a late colonizing legume shrub found in coastal sandy areas, endemic to the SW of the Iberian Peninsula and NW Morocco, has displayed invasive behavior in coastal dunes in different parts of the world, including its natural area of distribution. Its rapid expansion and increase in coverage has significantly contributed to the dune stabilization process, sometimes involving notable changes in the environment, plant community and shaping local distribution of some associated fauna, thus modifying the functioning of the whole ecosystem. In this review we examine the role of the expansion of R. monosperma in SW Spain coastal dunes, causes and implications, in the context of the ecological theory of invasions, and comparing it with other case studies.     

The growth responses of coastal dune species are determined by nutrient limitation and sand burial

Past work suggests that burial and low nutrient availability limit the growth and zonal distribution of coastal dune plants. Given the importance of these two factors, there is a surprising lack of field investigations of the interactions between burial and nutrient availability. This study aims to address this issue by measuring the growth responses of four coastal dune plant species to these two factors and their interaction. Species that naturally experience either high or low rates of burial were selected and a factorial burial by nutrient addition experiment was conducted. Growth characteristics were measured in order to determine which characteristics allow a species to respond to burial. Species that naturally experience high rates of burial (Arctotheca populifolia and Scaevola plumieri) displayed increased growth when buried, and this response was nutrient-limited. Stable-dune species had either small (Myrica cordifolia, N-fixer) or negligible responses to burial (Metalasia muricata), and were not nutrient-limited. This interspecific difference in response to burial and/or fertiliser is consistent with the idea that burial maintains the observed zonation of species on coastal dunes. Species that are unable to respond to burial are prevented from occupying the mobile dunes. Species able to cope with high rates of burial had high nitrogen-use efficiencies and low dry mass costs of production, explaining their ability to respond to burial under nutrient limitation. The interaction between burial and nutrient limitation is understudied but vital to understanding the zonation of coastal dune plant species.     

Wet dune slacks: decline and new opportunities

For a number of infiltrated coastal dune areas it is discussed to what extent artificial infiltration for the public water supply affects the quality of soil, groundwater and vegetation around pools and ponds, and what its effect is on the vegetation. Further, the results of investigations into the quality of vegetation, soil and water of a number of non-infiltrated, less affected dune areas are presented. The emphasis is on changes in groundwater flow pattern and on changes in the chemical composition of groundwater on the vegetation of wet dune slacks. Finally, recommendations for the management of wet dune slacks are presented. It can be concluded that the introduction of nutrients through infiltration causes an abundance of nitrophilous herbaceous vegetation along the banks of all infiltration ponds and most dune pools. Of the three investigated macro-nutrients, nitrate, potassium and phosphate, the latter shows the most significant correlation with the composition, cover and biomass of the vegetation. The moist biotopes of non-infiltrated dunes have largely disappeared because of desiccation, mainly as a consequence of water withdrawal, afforestation and coastal erosion. Relatively unaffected dune slacks can be found in the dunes on the Dutch Wadden Sea islands and a small number of dune areas on the mainland. In most areas, however, a serious decline in many rare species has been observed during the past twenty years because of eutrophic and acid precipitation, often in combination with disturbances of the groundwater regime.     

Limiting factors for seedling emergence and establishment of the invasive non-native Rosa rugosa in a coastal dune system

The relative importance of seed, habitat and microhabitat limitation has rarely been investigated for invasive non-native species, although this is critical for their effective management and for predicting future range expansion. Rosa rugosa is an abundant non-native shrub in coastal habitats of NW Europe; it is common along the Baltic coast but more scarce in exposed dunes of the North Sea. To investigate whether invasion of exposed dunes is limited by seed, habitat and microhabitat limitation, seedling emergence and establishment were examined in a factorial sowing, transplant and disturbance experiment. Twenty plots were randomly placed in each of five dune habitats (white dune, Empetrum dune, grey dune, outer dune heath, inner dune heath), and studied over 2 years. Seedling emergence in control subplots was zero in all habitats, whereas 96% and 98% of the undisturbed and disturbed seeded subplots produced seedlings. Disturbance had a positive effect on emergence and subsequent survival in white dune, outer and inner dune heath. Seedling survival and growth, and growth of transplanted seedlings, were markedly lower in grey dune. These findings indicate that establishment of R. rugosa is seed-limited in coastal dune habitats, and that the species is able to establish in both active and fixed dunes once seeds have arrived. Although differential seedling emergence and growth indicate that habitats differ in their degree of invasion susceptibility by R. rugosa, the positive influence of small-scale disturbance suggests microhabitat limitation in some dune habitats as well. Dune management should aim to reduce seed production and dispersal of R. rugosa in near-natural sites, and anthropogenic changes of habitat dynamics should be prevented.