Vegetation dynamics on the Łeba Bar/Poland: a comparison of the vegetation in 1932 and 2006 with special regard to endangered habitats

Coastal dune ecosystems are among the most dynamic habitats with high conservation value in Europe but are also under strong anthropogenic pressure regarding coastal protection and recreation. Hence, it is of high importance to know about long-term natural and anthropogenic changes and development of protected dune habitats for nature conservation, as well as for coastal management. This paper aims to identify the vegetation dynamics on the Łeba Bar/Poland over a period of 74 years by cartometric comparison using modern Geographical Information System (GIS). To quantify the rate of vegetation dynamics two aerial photographs dating from 1932 and 2006 were digitalized and analyzed with GIS to produce digital vegetation maps. Information about decrease, increase and stability of vegetation types of this area are discussed. The results show that there has been a clear reduction in the total area of bare sand and a considerable increase of woodlands and dense grass communities. Nevertheless, the remaining extensive drift sand areas and deflation hollows on the Łeba Bar offer one of the most important habitats for pioneer vegetation on bare sand of migrating dunes and dunes at the Southern Baltic coast. The present work proved the need to observe the future development of the vegetation communities and to implement management measures to maintain the dynamic of this unique dune landscape.     

Ecology, management and monitoring of grey dunes in Flanders

Grey dunes are a priority habitat type of the European Union Habitats Directive and demand special attention for conservation and management. Knowledge of the ecology of coastal grey dunes can contribute to this policy. Dune grassland succession is initiated by fixation and driven by the complex of soil formation (humus accumulation) and vegetation development. Leaching and mobilization of CaCO₃. which are important in nutrient dynamics, complicate the picture. At present, grass- and scrub encroachment greatly overrules these fine scaled soil processes and causes substantial loss of regional biodiversity. Belgium has an international responsibility in grey dune conservation because of the limited range of its characteristic vegetation, flora and fauna. As biomass removal seems essential in grassland preservation, grazing is an important management tool. Evaluation of management measures focuses on biodiversity measurements on the levels of landscape, community and species.     

The role of archaeophytes and neophytes in the Dutch coastal dunes

The position of alien plant species in the Dutch coastal dune vegetation is evaluated considering 12 archaeophytes and 20 neophytes (including one moss), all of widespread occurrence in the coastal area of the Netherlands. Almost all archaeophytes have become part of natural vegetation types. Open scrub communities, in particular Hippophae rhamnoides-Sambucus nigra scrub at the leeside of the outer dunes, and calciphilous moss-dominated pioneer vegetation are relatively rich in archaeophytes. Among neophyte vascular species a contrast is apparent between herbaceous and woody species. The majority of herbaceous neophytes are characteristic of man-disturbed habitats and are only infrequently observed in natural vegetation types. However, woody species (as well as the moss Campylopus introflexus) have entered into natural vegetation on a large scale and behave in an invasive way.     

The role of European marram grass in dune stabilization and succession near Cape Agulhas, South Africa

The coastline near the southern tip of Africa is characterized by large mobile dunes that are driven along wide beaches by strong winds throughout the year. This results in the blockage of the river mouths causing severe flooding of the low-lying farmland of the Agulhas Plain during the rainy winter season. Large parts of the driftsands were stabilized with the European dune pioneer species Marram grass (Ammophila arenaria), which has proved highly invasive along the North American west coast. In order to establish the potential invasiveness ofA. arenaria in South African coastal dune systems and its role in the succession of a large stabilization area, studies were carried out on De Mond Nature Reverve. Using aerial photos, maps and planting records, the vegetation of sites of various ages were sampled. By means of this chronosequence of stands, there is clear evidence that succession takes place at De Mond. Four communities are distinguished, varying from recent plantings ofA. arenaria to mature dune thicket or dune fynbos (heath) vegetation. These relate to four different stages of succession,A. arenaria occurring in reduced abundance in the older communities. After 50 years, formerA. arenaria areas are usually covered by dense dune scrub and in some places even in asteraceous dune fynbos. Succession is most rapid in sheltered, moist dune slacks, butA. arenaria remains vigorous in conditions favourable for its growht, i.e. on exposed, steep dune slopes with strong sand movement.A. arenaria does not appear to spread unaidedly at De Mond and has been successfully used for temporary dune stabilization.     

Lichens as indicators of a perturbation/stability gradient in the Asperillo dunes, SW spain

In the asperillo dune system, Southwest Spain, lichen vegetation covering the dune sand, has a low species diversity but is an important component of the perennial vegetation, providing stability, nutrients, and moisture to the soil layer. The Asperillo dunes harbour (1) natural ecosystems, (2) disturbed systems affected by forestry activities where the natural vegetation is eliminated, and (3) pine forest resulting from afforestation withPinus pinea since the end of the 1940s where the composition and abundance of the lichen flora has been drastically changed. Our hypothesis was that the lichen species composition and distribution are influenced by the type and period of human intervention. To test this hypothesis a 1.2 km × 1.1 km area, which includes zones with different degrees of conservation and perturbation, consisting of five different habitats, was selected: well preservedJuniperus woodland,Pinus pinea plantations with dense scrub, dense scrub,P. pinea plantations cleared from scrub, and pioneer scrub in recent pine afforestation. In each area, randomly located 5m × 5 m homogeneous plots were sampled. In each plot the cover of shrub and lichen species was recorded. The first results show that lichen cover is higher in the most preserved areas,Cladonia mediterranea being the dominant species under theJuniperus phoenicea canopy. The lichen community changes in composition and abundance depending on the time elapsed since the last perturbation.     

Development of new dunes in the Dutch Delta: nature compensation and ‘building with nature’

A new dune area was constructed by beach and foreshore nourishments along the Delfland Coast in the southwestern Netherlands. The new area is intended to be a compensation for losses of existing high quality dunes in nearby areas, due to the use/construction of Maasvlakte 2, the new harbour extension of Rotterdam opening in 2013. The target habitats for compensation include dry grey dunes and moist dune valley grassland. Due to the habitat type, the nourished material had to have a special character. The nourishment was carried out according to a special design and initial development of the new area had to follow certain pathways. In order to meet the compensation requirements in time. Careful monitoring is done to assess whether development of the new habitat is taking place in the direction of the desired target habitats. This paper reports on the construction of the new area and on the first years of development and monitoring. The monitoring mainly concerns development of the abiotic landscape elements, geomorphology, groundwater and soils. The lessons learned from this area are discussed in the light of the development of other recent young nature areas in the sandy Dutch delta coast. This gives new insights for coastal management in general in the context of building with nature.     

Vegetation succession and lichen diversity on dry coastal calcium-poor dunes and the impact of management experiments

The negative impact of grass and moss encroachment on the botanical diversity of West European coastal dunes attracted increasing attention in the 1990s. This paper focuses on moss encroachment during primary succession in the xeroseries. Until the mid-1970s, vegetation types rich in species of the lichen generaCladonia andCladina were found on the fixed,Corynephorus canescens-dominated, so-called grey dunes all over the island of Terschelling, The Netherlands. In addition, species ofHypogymnia, Parmelia andUsnea, which usually grow on trees, occurred here terrestrially on moss carpets or bare sand. These vegetation types are still present on the Noordsvaarder, a nature reserve in the western part of the island. They occur on parts of seven dune ridges parallel to the coast and form a chronosequence in which age increases with distance from the sea. Our study found the highest lichen diversity on the second and third dune ridges in a stage of primary succession that can be assigned to theViolo-Corynephoretum. The changes from lichen-rich to moss-dominated stadia were significantly related to soil development and acidification in connection with the ageing of the dune soil. The superficial cutting of sods in moss-encroached vegetation appeared to be unsuccessful as a management technique for restoring the biodiversity of cryptogams. Our findings suggest that the best option for maintaining lichen vegetation in theViolo-Corynephoretum is the blow-in of sand with a subneutral or neutral pH from reactivated and natural blowouts or from foredunes, with increasing lime content respectively.     

Influence of infrastructure development on the vegetation community structure of coastal dunes: Jeffreys Bay,South Africa

Coastal dunes are increasingly at risk due to pressures deriving from global climate change, sea level rise, recreation and development. The consequences of the “coastal squeeze” in which dunes are placed, such as erosion and the loss of critical ecosystem services, are usually followed by expensive restoration and protection measures, many of which are unsuccessful. Due to the poor understanding and acknowledgement of the key attributes of coastal dunes in decision making processes, it is essential to provide scientific data on the impacts of human interference on coastal dunes so as to inform executives and guide them towards a sustainable management of the coastal zone. The aim of this study was to investigate the impact of five different levels of infrastructure development on the vegetation community structure of coastal dunes in Jeffreys Bay, South Africa. The effects of infrastructure development on dune vegetation were quantified by measuring the richness, diversity, cover, height and composition of plant species. With an increase in infrastructure development a significant decrease in dune width, average species richness and height of the plants occurred, accompanied by a shift in plant community composition. The foredunes that were backed immediately by infrastructure presented significantly greater species richness, diversity, cover and height compared with the foredunes abutted by primary dunes. This study demonstrated that coastal dunes are environments which are sensitive to varying levels of human impact. Informed and comprehensive management planning of these environments is therefore imperative for the restoration and maintenance of remnant dunes and for the conservation of undeveloped coastal dunes.     

Biophysical feedback mediates effects of invasive grasses on coastal dune shape

Vegetation at the aquatic-terrestrial interface can alter landscape features through its growth and interactions with sediment and fluids. Even similar species may impart different effects due to variation in their interactions and feedbacks with the environment. Consequently, replacement of one engineering species by another can cause significant change in the physical environment. Here we investigate the species-specific ecological mechanisms influencing the geomorphology of U.S. Pacific Northwest coastal dunes. Over the last century, this system changed from open, shifting sand dunes with sparse vegetation (including native beach grass, Elymus mollis), to densely vegetated continuous foredune ridges resulting from the introduction and subsequent invasions of two nonnative grass species (Ammophila arenaria and Ammophila breviligulata), each of which is associated with different dune shapes and sediment supply rates along the coast. Here we propose a biophysical feedback responsible for differences in dune shape, and we investigate two, non-mutually exclusive ecological mechanisms for these differences: (1) species differ in their ability to capture sand and (2) species differ in their growth habit in response to sand deposition. To investigate sand capture, we used a moveable bed wind tunnel experiment and found that increasing tiller density increased sand capture efficiency and that, under different experimental densities, the native grass had higher sand capture efficiency compared to the Ammophila congeners. However, the greater densities of nonnative grasses under field conditions suggest that they have greater potential to capture more sand overall. We used a mesocosm experiment to look at plant growth responses to sand deposition and found that, in response to increasing sand supply rates, A. arenaria produced higher-density vertical tillers (characteristic of higher sand capture efficiency), while A. breviligulata and E. mollis responded with lower-density lateral tiller growth (characteristic of lower sand capture efficiency). Combined, these experiments provide evidence for a species-specific effect on coastal dune shape. Understanding how dominant ecosystem engineers, especially nonnative ones, differ in their interactions with abiotic factors is necessary to better parameterize coastal vulnerability models and inform management practices related to both coastal protection ecosystem services and ecosystem restoration.     

Conservation and management-oriented ecological research in the coastal zone of Baja California, Mexico

This paper presents the main results of two studies of contrasting natural and man-induced conditions along the Pacific coast of Baja California (Mexico), based on the assumption that ecological insight can be obtained from man-induced modifications insofar as relevant activities are explicitly addressed as parts of the systems under study. The study is concerned with a fragmented coastal succulent-sage scrub and showed that several patches of different size and age may harbor as many species as non-fragmented areas, and that 83% of the original species assemblage persisted in the fragments, in which the invasion by opportunistic exotic species may not progress beyond certain limits. The study of dune-backed and urban-backed beaches showed a significantly greater abundance of the Snowy Plover (Charadrius alexandrinus) at the dune-backed beach, where a much more active back-shore feeding of adult birds and the only evidences of breeding occurred. Both studies refer to landscape features of regional concern and its results may be used in conservation management. The results on fragmented coastal succulentsage scrub may encourage alternative urban designs that keep patches of the original landscape, thus meeting existing requirements of low density urban development for most of the coastal succulent-sage scrub area. The evidence presented on the negative effects of dune destruction on the abundance, feeding and reproductive performance of a threatened bird species has a bearing on the topic of biodiversity management. It may also contribute to the conservation of the coastal dunes system.     

Vegetation succession and lichen diversity on dry coastal calciumpoor dunes and the impact of management experiments

The negative impact of grass and moss encroachment on the botanical diversity of West European coastal dunes attracted increasing attention in the 1990s. This paper focuses on moss encroachment during primary succession in the xeroseries. Until the mid-1970s, vegetation types rich in species of the lichen generaCladonia andCladina were found on the fixed,Corynephorus canescens-dominated, so-called grey dunes all over the island of Terschelling, The Netherlands. In addition, species ofHypogymnia, Parmelia andUsnea, which usually grow on trees, occurred here terrestrially on moss carpets or bare sand. These vegetation types are still present on the Noordsvaarder, a nature reserve in the western part of the island. They occur on parts of seven dune ridges parallel to the coast and form a chronosequence in which age increases with distance from the sea. Our study found the highest lichen diversity on the second and third dune ridges in a stage of primary succession that can be assigned to theViolo-Corynephoretum. The changes from lichen-rich to moss-dominated stadia were significantly related to soil development and acidification in connection with the ageing of the dune soil. The superficial cutting of sods in moss-encroached vegetation appeared to be unsuccessful as a management technique for restoring the biodiversity of cryptogams. Our findings suggest that the best option for maintaining lichen vegetation in theViolo-Corynephoretum is the blow-in of sand with a subneutral or neutral pH from reactivated and natural blowouts or from foredunes, with increasing lime content respectively. Nomenclature: Van der Meijden (1990) for higher plants; Touw & Rubers (1989) for mosses; Purvis et al. (1992) for lichens. A set of lichen specimens has been deposited at the herbarium of Dr. A. Aptroot (C.B.S. Baarn) — herbarium code ABL (Taxon 44: 258).     

The development and application of remote sensing to monitor sand dune habitats

Sand dunes are complex systems that contain several habitats, often as mosaics or transitions between types. Several of these habitats are afforded protection under European Legislation and in the UK nationally within Special Areas of Conservation (SAC) and Sites of Special Scientific Interest (SSSI). Natural England has a statutory duty to report to Europe on the conservation status and condition of sand dunes; and is required to report to the UK Government on designated sites. To achieve this we have sought ways of capturing, analysing and interpreting data on the extent and location of sand dune habitats. This requires an ability to be able to obtain data over large areas of coastline in an efficient way. Natural England and Environment Agency Geomatics have worked collaboratively for over 16 years, sharing data and ecological knowledge. In 2012 work started to evaluate the use of remote sensing to map UK BAP and Annex I sand dune habitats. A methodology has now been developed and tested to map sand dune habitats. The key objective was to provide an operational tool that will help to map these habitats and understand change on sites around England. This has been achieved through analysis of LIDAR and Compact Airborne Spectrographic Imager (CASI) data using Object Orientated Image Analysis. Quality Control (QC) and accuracy assessments have shown this approach to be successful and 11 sites have been mapped to date. These techniques are providing a new approach to monitoring change in coastal vegetation communities and informing management of protected sites.     

The importance of coastal sand dunes for terrestrial invertebrates in Wales and the UK,with particular reference to aculeate Hymenoptera (bees,wasps &; ants)

Although most UK sand dune systems are now fossilized, with little mobility and reducing amounts of bare sand, they support important populations and assemblages of terrestrial invertebrates. Offering open conditions, warm substrates and a range of habitats and habitat structures, they have become increasingly significant as other coastal habitats have been lost. In Wales, 680 Red Data Book and Nationally Scarce species have been recorded from dunes. 109 species in the UK are restricted to dunes, and in Wales there are an additional 145 species confined to dunes and 208 species strongly associated with dunes. Of these, 172 species are dependent upon bare and sparsely-vegetated sand, in grey dunes and early-successional dune grassland, at some stage of their life cycle, rising to 292 species if those associated with the strandline, foredunes, yellow dunes and pioneer dune slacks are included, equating to 63% of the 462 dune species. Bees and wasps are particularly well represented, with 278 species (68% of the Welsh fauna) recorded on Welsh dunes, including 17 obligates and 44 species with a strong dependence, 52 of which are associated with bare and sparsely-vegetated sand. Key to maintaining invertebrate populations on UK dunes is the provision of bare sand but in Wales, bare sand accounts for only 1.7% of the total sand dune resource. As a more appropriate bare sand threshold is likely to range between 10 and 30%, radical action is required to re-mobilize at least the key sand dune systems.     

Conservation and management of the mediterranean coastal sand dunes in Israel

The aims of this study are to review the current situation of the Israeli Mediterranean coastal sand dunes, to examine the causes for this situation, and to propose options for future conservation and management of the protected dune areas based on ecological, environmental, landscape and recreational demands and interests. The coastal dunes of Israel are characterized by diverse plant communities, with 173 plant species occurring on sand (8.2% of the total flora of Israel) including many endemic species (26% of all endemic species in Israel). Most of the species are annuals. The importance of the coastal strip as a centre of floral and faunal speciation is also manifested in the existing sand-bound animals. However, many species are rare. This is mainly due to the extensive industrial and urban development along the coastal plain and the direct and indirect destruction of the remaining open dune areas by tourism, recreation and sand mining. Only ca. 17% of the Israeli coastal dunes are still of good or reasonable ecological value, while < 5% of this area has been designated as protected area. Management policies differ from place to place and depend on local objectives. These objectives derive mainly from the knowledge and data that exist for each location, and its statutory status. Since 1995 several projects, which aim to develop integrated management tools for nature conservation and recreation uses for all coastal sand dunes in Israel have been conducted. These projects are summarized in the present paper.     

Coastal dune stabilization in Wales and requirements for rejuvenation

Welsh coastal dune systems have become increasingly vegetated in recent decades. Several rare species of plants and invertebrates have declined dramatically in abundance, and in some areas lost entirely. Of the ten dune habitats and species recognized as being features of European importance within the Welsh Natura 2000 sites, nine are currently in Unfavourable condition on at least one site. The decline in active aeolian processes has also reduced the geomorphological interest of the sites, several of which were designated as Geological Conservation Review sites principally on the basis of their physical processes and landforms. The decline in bare sand area between the 1940-50s and 2009 has been quantified at twelve Welsh dune sites using aerial photography and GIS. The decline ranged from 41 % at Gronant Dunes and Talacre Warren to 97 % at Kenfig Burrows, with an average of 81 %. Morfa Dyffryn had the highest remaining percentage of bare sand in 2009 (20 %), with 30–40 % coverage of mobile dune and pioneer communities, while seven sites had < 5 % bare sand. Dune stabilization over the past 60 years has been favoured by a number of factors, including less windy conditions, higher temperatures and longer growing season, increased atmospheric nitrogen deposition, a reduction in grazing intensity, and dune management policies aimed at controlling mobile sand. Climate change projections suggest that, in the next 50 to 100 years, Wales and adjoining areas are likely to experience higher temperatures and higher rainfall, especially in winter, and a further slight reduction in wind speeds. Without intervention, dune and dune slack habitats are likely to be increasingly replaced by fixed dune grassland and scrub, resulting in the extinction of rare plants, invertebrates and other species which require open, mobile conditions. Several intervention options exist, ranging in scale and potential impact. Increased livestock grazing, re-introduction of rabbits, scrub clearance, turf stripping and the creation of shallow ‘scrapes’ can be beneficial but will not by themselves create self-sustaining mobile dunes. In order to have any chance of achieving any significant impact, larger-scale intervention measures, involving large-scale vegetation removal and sand-re-profiling, will be required. At least in the short-term, maintenance measures will be required to prevent vegetation re-growth, and the challenge will be to encourage the development of mobile dune features which will be naturally mobile in the medium to longer term.     

Possible impact of sea-level rise on some habitat types at the Baltic coast of Denmark

According to estimates from the Danish Meteorological Institute global warming until 2080 may cause a relative sea-level rise in Danish waters of 33–46 cm. In the present paper the possible impact of a sea-level rise of this magnitude on coastal habitat types is discussed for three case studies, based on previous investigations of vegetation, topography and soil of localities at the Baltic coast of Denmark. The case studies include the following types of localities and habitats: (1) an off-shore barrier complex: sandy beach, sand dune, geolittoral, brackish, low-tidal meadow, reed bed; (2) a protected bay: geolittoral, brackish meadow, coastal grassland; (3) a dune area: mobile and fixed dune communities, and adjoining sea wall: coastal grassland. In the geolittoral meadow and coastal grassland habitats the sea-level rise is expected to cause a horizontal displacement of vegetation zones and a reduction in area, depending on accretion rate (sedimentation, peat formation), local topography and inland land-use. In the beach and sand dune habitats the sea-level rise is expected to cause a change in groundwater level, influencing slack vegetation, and a change in the erosion/accretion pattern, resulting in landward rebuilding of the mobile dune as well as in a more or less diffuse inland sand drift, causing destabilization of fixed dune vegetation.     

Beach vulnerability assessment of a protected area of the Northern Campania coast (Southern Italy)

A detailed and multidisciplinary study of physical and biotic factors of a coastal sector of southern Italy, the Pineta della foce del Garigliano SCI (Site of Community Importance) area, has been carried out in the frame of the European research project LIFE + Nature & Biodiversity PROVIDUNE. We evaluated the degree of dunes vulnerability (Dune Vulnerability Index, DVI) and sustainable anthropogenic load (carrying capacity) of the emerged beach of the study area, which is largely affected by shoreline retreat and degradation of dune habitat. The values of about 0.6 of the DVI in the two key sectors of the study area suggest a high level of vulnerability of beach/dune system due to both natural and human factors. The partial vulnerability index related to the geomorphological condition exhibits the highest values, as a consequence of a coastal system largely affected by recent and present-day beach erosion and severe hydrodynamics processes. Several inadequate human practises have been recognized in the study area whose impact appears to be an important factor in controlling the reduction of the beach-dune system resilience. Integrated analysis of DVI and carrying capacity suggests that the northern and central sectors of the study area have a high level of dune vulnerability due to hydrodynamic and geomorphological factors whereas the human impact can be considered relatively less important. The southern sector of the study area is featured by a well-developed infrastructure system, which is able to assure a sustainable beach occupation. Nevertheless, significant interventions such as dune replacement by permanent or ephemeral infrastructures, uncontrolled pedestrian or vehicular access and inappropriate use of mechanical beach cleaning have been recognized in this sector of the beach. These long-lasting impacts have promoted the dismantling of large sector of the dune habitats. Obtained results allowed identifying the critical area where appropriate actions can be performed for the mitigation of impacts, the conservation of dune habitats and their sustainable use.     

Site specific factors have an overriding impact on Baltic dune vegetation change under low to moderate N-deposition—a case study from Hiddensee island

At three coastal dune sites at the island of Hiddensee, north-east Germany, vegetation cover was mapped during 2002 and compared to vegetation surveys from the late 1980s and 1930s. Abiotic and biotic factors, which have been identified as being critical for coastal dunes in former studies such as disturbance, salt spray or nutrient availability, were measured. Grazing and land-use history were reviewed by literature and interviews. Tall graminoid communities, mainly Carex arenaria, are a common vegetation unit today. Development, distribution of these dominances and possible causes for its occurrence have not been analysed. Generally, older successional vegetation units increased and pioneer stages decreased from the 1930s until 2002. At the geologically youngest site, the southern dunes, grass encroachment by Carex arenaria was highest (ca. 50% cover in 2002), and age and density of trees lower than at the older, central dunes. Land-use changes such as decrease in grazing pressure, additional feeding of livestock, increase in coastal protection measures and subsequent decrease in shifting sands as well as varying availability of groundwater and amount of salt spray are relevant factors for vegetation changes in coastal dunes over the past 70 years. Site-specific land-use differences such as livestock density and land-use history have a stronger influence than atmospheric N-pollution on the vegetation composition of these acidic, coastal dunes under low to moderate N-deposition loads of 6–8 kg N ha⁻¹ yr⁻¹.     

From overexploitation to sustainable use,an overview of 160 years of water extraction in the Amsterdam dunes,the Netherlands

Dune slacks are low-lying, nutrient-poor, species-rich, inter-dunal, seasonally flooded wetlands, are amongst the most threatened habitats in the Dutch coastal dunes. Since 1853 Waternet has been extracting groundwater from the coastal dunes southwest of Haarlem to produce its drinking water. Dune slacks largely disappeared due to the desiccation caused by this water abstraction, over more than a century biodiversity declined as a consequence. Increased societal concern pushed habitat restoration high on the political agenda by the end of the 1980s. It was agreed to do what is possible to restore original dune slacks without endangering the water supply. Far reaching interventions in the dune water system were foreseen to achieve this mutual goal. To allow reliable decision making, the entire hydrological history of the drinking water production in the Amsterdam Dunes since 1853 and its ecological consequences were evaluated over a 10-year study period. The main tool was a 3D groundwater model constructed using all information gathered to date and calibrated using the long-term monitoring data available and widely extended for the purpose, to which ecological modeling was added and calibrated with the available long-term and extended vegetational inventories. These scientific tools were used to assess proposed interventions to be decided upon, which aimed at finding a new balance between groundwater extraction and nature restoration. In 1996 and 2007 large-scale measures were taken, which include filling in of recovery canals, mowing, grazing and sod-cutting to support the native plant communities of wet dune slack habitats. Results of these measures in terms of the restoration of natural hydrological conditions are shown together with the first results for the recovery of wet slacks vegetation that resulted from the combined hydrological and ecological restoration measures that were taken since 1995.     

Management of basiphilous dune slack communities in relation to carbonate accumulation and hydrological conditions

In dune slacks in The Netherlands, a decline of rare mesotrophic basiphilous plant species and their plant communities has been observed in combination with an increase of more productive systems with common, taller acidophilous plant species. This has been attributed to both natural and anthropogenic changes. In a humid climate with a precipitation surplus, as in The Netherlands, the calcium carbonate content of a calcareous soil increases with depth. However, soils in coastal dune slacks, may have a higher carbonate content in the topsoil horizon than in the underlying layers. Carbonates which buffer the pH can prolong the presence of mesotrophic basiphilous plant communities which are of high conservation value. To explain the occurrence of calcareous surface horizons in dune slacks, hydrological and micromorphological analyses were carried out in three dune slacks. Two slacks are situated on the Wadden Sea islands in the northern part of The Netherlands; one on Schiermonnikoog and one on Texel. The third slack is situated in the dunes on the island of Goeree in the southwestern part of The Netherlands. In all three slacks, carbonate occurs as mollusc and gastropod fragments (silt- or sand-sized) and as micritic nodules in the topsoil layer, due to aeolian deposition and sedimentation by water.In situ carbonate accumulation (calcitans and calcareous crusts) due to CO₂ release in inundated and/or capillary rise of calcareous groundwater near, or at the soil surface. Accumulation of carbonate also occurs as a result of biological activity by algae in the topsoil of the Goeree site. In general, hydrological processes maintaining high levels of calcareous groundwater are a prerequisite for the maintenance of high carbonate levels in topsoils. Such levels are necessary for the conservation and management of basiphilous pioneer vegetation.