Angus Garbutt

The natural regeneration of salt marsh on formerly reclaimed land

ABSTRACT Question: Does the vegetation of restored salt marshes increasingly resemble natural reference communities over time? Location: The Essex estuaries, southeast England. Methods: Abandoned reclamations, where coastal defences had been breached in storm events, and current salt marsh recreation schemes were surveyed giving a chronosequence of salt marsh regeneration from 2 to 107 years. The presence, abundance and height of plant species were recorded and comparisons were made with adjacent reference salt marsh communities at equivalent elevations. Results: Of the 18 paired sites surveyed, 13 regenerated marshes had fewer species than their adjacent reference marsh, three had an equal number and two had more. The plant communities of only two de-embankment sites matched that of the reference community. 0–50 year old sites and 51–100 year old sites had fewer species per quadrat than the 101+ year sites and the reference salt marshes. There was a weak relationship between differences in species richness for regenerated and reference marshes and the time since sites were first re-exposed to tidal inundation. Cover values for the invasive and recently evolved Spartina anglica were greater within regenerated than reference marshes. Conclusions: Salt marsh plants will colonise formerly reclaimed land relatively quickly on resumption of tidal flooding. However, even after 100 years regenerated salt marshes differ in species richness, composition and structure from reference communities. Nomenclature: Rodwell (2000) for plant communities, Stace (1997) for vascular plants and Hardy & Guiry (2003) for algae.

Grazing management in saltmarsh ecosystems drives invertebrate diversity, abundance and functional group structure

Abstract.  1. Saltmarsh conservation management often involves livestock grazing to maximise plant diversity and provide suitable breeding habitat for over‐wintering coastal birds. The effect of grazing on invertebrates is rarely quantified, but results from limited studies of terrestrial and coastal grasslands demonstrate greater abundance and species richness in un‐grazed grassland.

Soil stabilization linked to plant diversity and environmental context in coastal wetlands

Abstract Background Plants 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. Question We hypothesize that soil erosion rates fall with increased plant species richness, and test explicitly how closely root biomass is associated with plant diversity. Methods We 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. Results Soil 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. Conclusion Our 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.

Continued declines of Redshank Tringa totanus breeding on saltmarsh in Great Britain: is there a solution to this conservation problem?

Capsule: Over 50% of saltmarsh breeding Common Redshank have been lost since 1985, with current conservation management having only limited success at halting these declines. Aims: To update population size and trend estimates for saltmarsh-breeding Redshank in Britain, and to determine whether conservation management implemented since 1996 has been successful in influencing grazing intensity and Redshank population trends. Methods: A repeat national survey of British saltmarsh was conducted in 2011 at sites previously visited in 1985 and 1996. Redshank breeding density and grazing pressure were recorded at all sites; the presence of conservation management was additionally recorded for English sites. Results from all three national surveys were used to update population size and trend estimates, and to investigate changes in grazing pressure and breeding density on sites with and without conservation management. Results: Of the 21 431 pairs breeding on saltmarsh in 1985, 11 946 pairs remained in 2011, with the highest proportion of this population found in East Anglia. From 1985, British breeding densities declined at a rate of 1 pair km−2 year−1, representing a loss of 52.8% of breeding pairs over 26 years, although regional trends varied across different time periods. Grazing pressures did not change markedly with conservation management. Redshank declines were less severe on conservation-managed sites in East Anglia and the South of England where grazing pressures remained low, though were more severe on conservation-managed sites in the North West where heavy grazing persisted. Conclusion: Saltmarsh-breeding Redshank declines continue and are likely to be driven by a lack of suitable nesting habitat. Conservation management schemes and site protection implemented since 1996 appear not to be delivering the grazing pressures and associated habitat conditions required by this species, particularly in the North West of England, though habitat changes may not be linked to unsuitable grazing management in all regions. An in-depth understanding of grazing practices, how conservation management guidelines could be improved, and the likely success of more long-term management solutions is needed urgently.

Success of managed realignment for the restoration of salt-marsh biodiversity: preliminary results on ground-active spiders

Abstract Since the early 1990s managed realignment, where formerly reclaimed land is re-exposed to tidal inundation through breaching of coastal embankments, has been increasingly used throughout Northern Europe as a cost effective and sustainable response to biodiversity loss and flood management. This study aimed to evaluate the success of managed realignment schemes that resulted in salt-marsh development for the restoration of spider assemblages. Restoration of salt-marsh fauna was studied by comparing ground-active spiders between recently inundated land (3–14 years old) and pair-matched, adjacent natural salt marshes. Natural reference salt marshes were characterized by a relatively low species richness, the dominance of late-successional stage species such as Pirata piraticus (Clerck 1757), and the presence of species preferring a closed vegetation canopy like Arctosa fulvolineata (Lucas 1846) and Pardosa nigriceps (Thorell 1856). Restored habitats were characterized by greater species richness than in reference habitat and by the presence of halophilic species (Enoplognatha mordax (Thorell 1875) and Erigone longipalpis (Sundevall 1830)) and abundance of Pardosa purbeckensis (Westring 1861). These preliminary results argue for maintaining a maximum of successional stages in salt marshes, as they increase the diversity of halophilic spiders.

European salt marshes: ecology and conservation in a changing world

Saltmarsh habitats have been studied and reported on in the scientific literature for over a century. The earliest papers were given over to descriptive studies of plant species zonation and distribution. As the science of ecology developed, experimental studies set out to understand the physical processes that play such an important part in the formation of salt marshes and their interaction with the biota. As the twentieth century progressed, ecological theory developed into its own branch of science and salt marshes, with their strong environmental gradients and relatively low number species richness, became ideal habitats to test the latest concepts. At the same time, there became greater awareness of the effects of estuarine and coastal zone degradation due to centuries of over-exploitation, habitat modification and pollution resulting in loss of biodiversity and habitat extent. Studies on habitat management and the restoration of biodiversity and natural processes began to influence policy makers and land managers. Today, there is a global and active science community involved in the descriptive, experimental, applied, theoretical and legislative disciplines of saltmarsh ecology. This special issue brings together some of these areas presented at the Coastal Ecology Workshop, an annual forum for scientists working on saltmarsh related topics throughout Northern Europe.

Nest trampling and ground nesting birds: quantifying temporal and spatial overlap between cattle activity and breeding redshank

Abstract Conservation grazing for breeding birds needs to balance the positive effects on vegetation structure and negative effects of nest trampling. In the UK, populations of Common redshank Tringa totanus breeding on saltmarshes declined by >50% between 1985 and 2011. These declines have been linked to changes in grazing management. The highest breeding densities of redshank on saltmarshes are found in lightly grazed areas. Conservation initiatives have encouraged low‐intensity grazing at <1 cattle/ha, but even these levels of grazing can result in high levels of nest trampling. If livestock distribution is not spatially or temporally homogenous but concentrated where and when redshank breed, rates of nest trampling may be much higher than expected based on livestock density alone. By GPS tracking cattle on saltmarshes and monitoring trampling of dummy nests, this study quantified (i) the spatial and temporal distribution of cattle in relation to the distribution of redshank nesting habitats and (ii) trampling rates of dummy nests. The distribution of livestock was highly variable depending on both time in the season and the saltmarsh under study, with cattle using between 3% and 42% of the saltmarsh extent and spending most their time on higher elevation habitat within 500 m of the sea wall, but moving further onto the saltmarsh as the season progressed. Breeding redshank also nest on these higher elevation zones, and this breeding coincides with the early period of grazing. Probability of nest trampling was correlated to livestock density and was up to six times higher in the areas where redshank breed. This overlap in both space and time of the habitat use of cattle and redshank means that the trampling probability of a nest can be much higher than would be expected based on standard measures of cattle density. Synthesis and applications: Because saltmarsh grazing is required to maintain a favorable vegetation structure for redshank breeding, grazing management should aim to keep livestock away from redshank nesting habitat between mid‐April and mid‐July when nests are active, through delaying the onset of grazing or introducing a rotational grazing system.

The importance of canopy complexity in shaping seasonal spider and beetle assemblages in saltmarsh habitats

1. Habitat structure, including vegetation structural complexity, largely determines invertebrate assemblages in semi‐natural grasslands. The importance of structural complexity to the saltmarsh invertebrate community, where the interplay between vegetation characteristics and tidal inundation is key, is less well known.