The restoration of coastal shingle vegetation: effects of substrate composition on the establishment of seedlings

  • Published source details Walmsley C.A. & Davy A.J. (1997) The restoration of coastal shingle vegetation: effects of substrate composition on the establishment of seedlings. Journal of Applied Ecology, 34, 143-153.


Study 1

Shingle beach vegetation at Sizewell, Suffolk, eastern England, was extensively damaged during construction of a power station. The feasibility of restoring the vegetation by directly sowing seeds of five species important in the existing plant communities, in field and glasshouse experiments was investigated. Summarised here are the results of the field trials.

Study site: The experiment examining the effects of substrate composition and effects of position relative to the sea on the establishment of seedlings was undertaken on the c. 50 m wide beach at Sizewell, eastern England (National Grid ref: TM 475635). Vegetation on this predominantly shingle beach (with some sandier areas) is dominated by a few clonal perennials e.g. sea sandwort Honckenya peploides, sea pea Lathyrus japonicus and marram grass Ammophila arenaria.

Experimental design: The field experiment examined the effects of proximity to the sea, composition of the beach substrate, and its amendment with organic matter on seedling emergence and establishment. Between 7 to 12 May 1991, on a sparsely vegetated, 15 x 15 m beach section from the strandline to the upper beach edge, a matrix of 1 x 5 m plots (separated by 0.5 or 1 m paths) parallel to the shoreline, was established. Each row and column contained: four untreated/unsown (control) plots (raked level, no other treatment); two untreated/sown plots; two organic matter treated/sown plots.

Seeded plots were sown by broadcasting and seed raked in. Organic matter plots received 50L of composted bark raked into the top 10 cm of shingle prior to seed sowing.

Seed preparation and sowing: In May 1991, species sown in a mix of unprepared seed were: sea kale Crambe maritima, sea holly Eryngium maritimum, yellow horned-poppy Glaucium flavum, sea pea Lathyrus japonicus and curled dock Rumex crispus ssp. littoreus. The seed was collected at Sizewell in 1986, stored, and at time of sowing were about 4.5 years old. Germination tests carried out prior to sowing resulted in the following percentage seed germination rates:

Crambe maritima - 59%

Eryngium maritimum - 22%

Glaucium flavum - 88%

Lathyrus japonicus - 91%

Rumex crispus - 100%

Topography and substrate: The site was surveyed on 7 May 1991 and 11-15 October 1993 to obtain topographic measurements of the beach profile. Substrate cores (10 cm diameter, 13 cm deep) were taken prior to sowing and particle size analysed by sieving and weighing.

Seedling emergence was recorded at 2-monthly intervals between February 1992 and February 1993. The few 1991 plants were visibly different from those emerging later, and were tagged as required for identification purposes. The reproductive capacity of G.flavum (which had the greatest emergence of the five species), was also estimated by recording the maximum reproductive stem height and number of pods per plant, and seedling growth was monitored.

Plant emergence: There was little emergence of seedlings during the first season (a few G.flavum and R.crispus seedlings only) and most occurred in the following spring, between February and April. A low percentage of the viable seeds of all five species had emerged even after two seasons (see below). Greatest emergence was of G.flavum (34% overall, rising to 62% in sandier plots), whereas the relatively long-lived perennials showed lower emergence (1.3-18%) and slower growth. Only G.flavum produced reproductive plants, in the second year.

Total emergence of viable seed sown for each of the five species was:

Crambe maritima - 18%

Eryngium maritimum - 4.7%

Glaucium flavum - 34%

Lathyrus japonicus - 1.3%

Rumex crispus - 9.5%

Effects of substrate: Seedling emergence was greater in organic matter treated plots for all species and most emerged better from sandy plots than shingle dominated plots. Although G.flavum emergence was greater in sandy plots (62%), seedling survivorship and growth were much greater in shingle plots.

Conclusions: Direct sowing of seeds on the beach at Sizewell resulted in poor overall establishment of the five species sown. This method therefore is not recommended as a general technique for the restoration of shingle beach vegetation, except for annual or monocarpic species (e.g. G.flavum). Amendment with organic matter provided little benefit that could not have been achieved more simply by the addition of beach sand to the coarsest shingle substrates.

Study 2

Shingle beach vegetation at Sizewell, Suffolk, eastern England, was extensively damaged during construction of a power station. The feasibility of restoring vegetation and identification of best techniques to employ was undertaken in a series of experiments. Summarised here are the results of a glasshouse experiment which examined the effects of sowing density and substrate texture on the survival of yellow horned-poppy Glaucium flavum.

Study site: The glasshouse experiment used yellow horned-poppy Glaucium flavum seed collected from the beach at Sizewell, Suffolk, eastern England (National Grid ref: TM 475635).

Poppy seed and sowing substrate: Yellow horned-poppy seed, 18 months old, was stratified at around 2ºC in sand for 23 weeks to break dormancy. On 24 January 1993, the seed was sown in 9-cm square pots (10 pots, five seeds each, thinned to one/pot after germination; five pots 10, 25, 50 and 100 seeds) containing either 100% washed horticultural sand or, 1 1:4 mix of sand and 5 mm grade shingle. The seed was sprinkled on the surface and covered in 2-4 mm of sand. The pots were kept in a heated (15ºC) illuminated (400 W sodium lamps 16 h/day) glasshouse. Pots were regularly watered and fed with liquid fertilizer.

Seedling emergence and survival: Seedling emergence and survival were recorded at first three times/week, and then at reduced frequency. The experiment ran over 22 weeks, at the end of which plants were dried and weighed to obtain shoot and root dry mass.

Percentage emergence was quite low, 51% in the sand substrate, and 44% in the shingle sand mix. The lower emergence in the latter is attributed to less water and seed retention in the surface shingle. However the surviving density of plants was greater in sand-shingle mix throughout the range of sowing densities. Seedlings also grew much less in the sand than in the sand-shingle mixture.

On shingle, survival was negatively density-dependent, but the much lower survival on sand was density-independent. Consequently, the higher mortality on sandy field plots was probably directly associated with substrate effects.

Study 3

During the construction of Sizewell 'B' power station in eastern England, a series of methods were investigated for the restoration of the distinctive plant communities of the shingle beach and dunes that would be needed after the inevitable severe disturbance to about 1 km of coastline. The use of container-grown plants in restoring shingle beach vegetation is summarised here.

Study site: The field experiment to examine the effects of organic matter and fertilizer additions on the establishment of six container-grown shingle beach plant species was undertaken on Sizewell beach (National Grid ref: TM 475635), Suffolk, eastern England, where a 1 km stretch of coastline had lost much of its plant cover due to disturbance by heavy machinery during construction of a power station.

Species and planting: Six plant species were selected from the natural vegetation community (number of plants in experiment in parenthesis): sea kale Crambe maritima (4), sea holly Eryngium maritimum (7), yellow-horned poppy Glaucium flavum (22), sea sandwort Honckenya peploides (17), sea pea Lathyrus japonicus (8) and curled dock Rumex crispus (5). Plants were raised from stored seed, indigenous to the site, using standard horticultural techniques. Plants were hardened-off and transferred outside in March, and were 31 weeks old at planting. The 16 plots were planted on 26-27 April and 2-3 May 1990.

Field experiments investigated the efficacy of organic matter and fertilizer treatments as ameliorants to the otherwise dry, nutrient-poor and heterogeneous physical composition of the beach shingle, and examined the influence of position on the beach profile and substrate composition on the establishment of container-grown plants.

Organic matter and fertilizer additions had no significant effect on average plant size in any species after one growing season. Planting location on the beach profile was the most important factor influencing establishment; C.maritima, G.flavum, H.peploides and R.crispus all grew significantly larger in the seaward plots, with more coarse shingle. Only G.flavum produced many reproductive plants during the first year, and these were more frequent and more fecund in the seaward plots.

The establishment of container-grown plants of four of the species was also compared at two sites at similar distances from the sea, one sandy and one shingle-dominated. Again, greater growth on the coarser shingle substrate by three of the most characteristic shingle beach species was observed. Thus, substrate physical composition was probably the primary determinant of differences in performance across the beach profile.

The use of container-grown plants to establish shingle vegetation resulted in low mortality, with rapid plant growth and establishment. Fertilizer and organic matter treatments were not generally cost-effective in establishing shingle beach vegetation from container-grown plants. The authors conclude that the use of resources to recreate an appropriate substrate composition is of far greater importance in restoration of plant communities of such habitats.

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