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Abstract:Coastal margin habitats are globally significant in terms of their capacity to sequester and store carbon, but their continuing decline, due to environmental change and human land use decisions, is reducing their capacity to provide this ecosystem service. In this paper the UK is used as a case study area to develop methodologies to quantify and calculate a monetary value for the service of carbon sequestration and storage in coastal margin habitats. Specific changes in UK coastal habitat area between 1900 and 2060 are documented, the long term stocks of carbon stored by these habitats are calculated, and the capacity of these habitats to sequester CO 2 is outlined. Changes in value of the carbon sequestration and storage service of coastal habitats were then projected for under two scenarios, the maintenance of the current state of the habitat and the continuation of current trends of habitat loss. If coastal habitats were to be maintained at their current extent, their sequestration capacity over the period 2000-2060 is valued to be in the region of £1-3 billion UK sterling. However, if current trends of habitat loss continue, the capacity of the coastal habitats both to sequester and store CO 2 will be significantly reduced, with a reduction in value of around £0.25 -1 billion . If loss-trends due to sea level rise or land reclamation worsen, this loss in value will be greater. This case study provides valuable site specific information, but also highlights global issues regarding the quantification and valuation of carbon sequestration and storage. Whilst our ability to value ecosystem services is improving, considerable uncertainty remains. If such ecosystem valuations are to be incorporated with confidence into national and global policy and legislative frameworks, it is necessary to further address this uncertainty. Recommendations on achieving this are outlined.3

BackgroundPlants play a pivotal role in soil stabilization, with above‐ground vegetation and roots combining to physically protect soil against erosion. It is possible that diverse plant communities boost root biomass, with knock‐on positive effects for soil stability, but these relationships are yet to be disentangled.QuestionWe hypothesize that soil erosion rates fall with increased plant species richness, and test explicitly how closely root biomass is associated with plant diversity.MethodsWe tested this hypothesis in salt marsh grasslands, dynamic ecosystems with a key role in flood protection. Using step‐wise regression, the influences of biotic (e.g. plant diversity) and abiotic variables on root biomass and soil stability were determined for salt marshes with two contrasting soil types: erosion‐resistant clay (Essex, southeast UK) and erosion‐prone sand (Morecambe Bay, northwest UK). A total of 132 (30‐cm depth) cores of natural marsh were extracted and exposed to lateral erosion by water in a re‐circulating flume.ResultsSoil erosion rates fell with increased plant species richness (R 2 = 0.55), when richness was modelled as a single explanatory variable, but was more important in erosion‐prone (R 2 = 0.44) than erosion‐resistant (R 2 = 0.18) regions. As plant species richness increased from two to nine species·m−2, the coefficient of variation in soil erosion rate decreased significantly (R 2 = 0.92). Plant species richness was a significant predictor of root biomass (R 2 = 0.22). Step‐wise regression showed that five key variables accounted for 80% of variation in soil erosion rate across regions. Clay‐silt fraction and soil carbon stock were linked to lower rates, contributing 24% and 31%, respectively, to variation in erosion rate. In regional analysis, abiotic factors declined in importance, with root biomass explaining 25% of variation. Plant diversity explained 12% of variation in the erosion‐prone sandy region.ConclusionOur study indicates that soil stabilization and root biomass are positively associated with plant diversity. Diversity effects are more pronounced in biogeographical contexts where soils are erosion‐prone (sandy, low organic content), suggesting that the pervasive influence of biodiversity on environmental processes also applies to the ecosystem service of erosion protection.

Summary1. Deliberate breaching of sea defences is frequently practised with the aim of restoring salt-marsh vegetation on previously embanked land. However, experience so far has shown that it may take several years before salt-marsh vegetation is fully established, and it is possible that limited diaspore dispersal plays a role in this. In order to ascertain whether salt-marsh development may be constrained by limited diaspore dispersal, we studied the dispersal of salt-marsh species by tidal water. 2. From October 2001 to the end of March 2002 a total of 38 species, of which 18 were salt-marsh species, was trapped in a restoration site and adjacent marsh. Aster tripolium , Limonium vulgare , Puccinellia maritima , Salicornia spp., Spergularia media and Suaeda maritima were the most abundant salt-marsh species, with more than 3 diaspores m − 2 trapped during the study period. 3. For most species, the number of diaspores trapped was representative of their abundance in nearby vegetation. Hence, despite the potential for long-distance transport by tidal water, our results indicate a predominantly local dispersal of salt-marsh species. Synthesis and applications.For the restoration of salt-marsh vegetation after deembankment, relatively rapid colonization may be expected from pioneer and low-marsh species, provided they are present in a nearby source area and the restoration site is at the appropriate altitude. The establishment of species absent from the adjacent marsh may be dependent on the presence of birds or humans as the main dispersal agents. Breaching of sea defences should preferably take place before or during September, in order to take advantage of the peak in dispersal of salt-marsh species in the first year after breaching.

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Summary 1.Restoration of salt marshes on previously reclaimed land provides an excellent opportunity to study plant colonization and subsequent development of salt-marsh vegetation. Insight into the process of salt-marsh development can guide the design, implementation and evaluation of salt-marsh restoration schemes and help determine appropriate management strategies. 2. We evaluated the process of salt-marsh restoration at a species-and plant-community level and investigated how the sequence of species establishment is related to site suitability, availability of the target species in the local and regional species pools and dispersal traits. 3. It took approximately 5 years for species diversity in the restoration site to become similar to a local reference marsh. The annual species Salicornia spp. and Suaeda maritima colonized and reached maximum abundance first. Perennial species ( Puccinellia maritima , Aster tripolium , Spartina anglica , Spergularia media , Atriplex portulacoides and Limonium vulgare ) only started to colonize or increase notably in abundance after 3 years of restoration. 4. Plant composition at the highest elevation of the restoration site developed from an annual Salicornia community into a Puccinellia maritima salt marsh, which was similar to the local reference marsh. After 8 years, the lower elevations were still covered by annual Salicornia salt marsh despite the potential for the development of a Puccinellia community. 5. Salt tolerance appeared to be much more important in explaining the sequence of species establishment than the availability of the species in the local or regional species pools or dispersal traits. 6. Synthesis and applications . The prospect of salt-marsh restoration after de-embankment is good, with target species establishing spontaneously and vegetation succession taking place. Because most salt-marsh species are dispersed over short distances, it is important that a well-developed salt marsh is adjacent to the restoration site. The rate of salt-marsh development and species diversity appears to be affected mainly by surface elevation. Proper elevation in relation to tidal inundation is therefore a prerequisite for the successful restoration of salt-marsh vegetation after de-embankment.

We evaluated the process of salt-marsh colonization in early successional stages and investigated how the sequence of species establishment was related to different success factors. Vegetation data were collected in the restoration site and in the adjacent salt marshes during three consecutive periods. Seed length, width and mass were used as dispersal traits, and Ellenberg moisture, salinity and nutrient indices as indicators of site suitability. Seed production in the reference site and seed bank in the restoration site were also investigated. The establishment of salt-marsh species in the restoration site was good and fast, the cover of new colonizers was unrelated to their cover in the restoration site at the first year. Seed availability appeared to be a more important factor in explaining the sequence of species establishment than salt and nutrient-limitation tolerance. Among dispersal and site traits, seed length and mass mainly indicated a relationship with new colonizers. We evaluated the process of salt-marsh colonization in early successional stages and 4 investigated how the sequence of species establishment was related to different success 5 factors. Vegetation data were collected in the restoration site and in the adjacent salt marshes 6 during three consecutive periods. Seed length, width and mass were used as dispersal traits, 7 and Ellenberg moisture, salinity and nutrient indices as indicators of site suitability. Seed 8 production in the reference site and seed bank in the restoration site were also investigated.9 The establishment of salt-marsh species in the restoration site was good and fast, the cover of 10 new colonizers was unrelated to their cover in the restoration site at the first year. Seed 11 availability appeared to be a more important factor in explaining the sequence of species 12 establishment than salt and nutrient-limitation tolerance. Among dispersal and site traits, seed 13 length and mass mainly indicated a relationship with new colonizers.14 15

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