Summary • Description • Constraints • Potential effects • Monitoring • Locations • Further information

Case Studies	Chichester Harbour, West Sussex
	Cleavel Point, Poole Harbour, Dorset

Summary

Vegetation planting can be used in a variety of situations as an exclusive technique or, more commonly, in combination with other restoration or habitat creation methods. Through deliberate planting, particularly using Spartina species, erosive tidal flows can be dissipated by the plant stems, with the resultant effects of a decrease in current velocity, increased sediment deposition and an increase in the level of the mudflats and marshes.

Saltmarsh vegetation can only be established successfully, however, if the physical as well as biological conditions are satisfactory. Natural colonisation should, therefore, be considered as the preferred option for saltmarsh vegetation establishment rather than artificial transplantation; although planting or seeding initiatives nonetheless may be useful in situations where there are no existing saltmarshes in the area and/or where natural colonisation is deemed to be undesirable from either a flood defence or a nature conservation perspective.

Description

Saltmarsh vegetation will establish in areas of suitable elevation with sufficient protection from high energy tides and waves. Rather than waiting for natural colonisation to occur, increased sediment stability and wave attention may be achieved by artificially encouraging the growth of saltmarsh plants.

However, there are a number of considerations that need to be taken into account in determining the suitability of vegetation planting as a saltmarsh management technique and the types of plants that should be used. In summary, the following should be considered:

• Is there a history of saltmarsh growth? This will mean that it can grow in the area, but will also provide a seed supply for marsh succession and development.
• Is the coastline experiencing rapid erosion? If so, a planted marsh may not survive long and landward realignment may be a better option.
• Is the mudflat to be planted at a suitable elevation? Existing marshes will help determine the elevation at which pioneer vegetation will first appear.
• Is the mudflat slope suitable for marsh succession?
• Is the salinity, hydrology and substrate suitable for vegetation?

Wave action and the influence of tidal range are the most important components in determining the type of plants that should be used (if any). Exposed shorelines with high wave energy, which are not afforded additional protection from wave breaks, may experience plant wash-out or low survival rates for species/individuals unable to tolerate wave stress. The elevation of the planted surface and the relationship with tidal range, which will influence potential survival rates, should be used to determine the species selected. This requires careful consideration, as inappropriate times and durations of submergence will cause plant mortality. The combination of elevation and shore morphology with a particular set of wave conditions can also greatly influence the stress placed on plants. Similarly, the salinity of the water and the substrate is important in determining species survival rates, since some species are better able to tolerate highly saline conditions than others.

The ability of Spartina spp to survive under a wide range of conditions and to propagate by rhizhome has led to its widespread use in the UK for planting. Spartina has demonstrated the ability to colonise in different locations and in different parts of the intertidal in relation to the tidal frame. It has, however, also died-back in places, remained moribund in others, and smothered other indigenous species elsewhere.

Click here for more information on the effects of Spartina

Constraints

As far as possible, species selected for planting should represent the natural species assemblage for the area, in order to avoid the introduction of exotic species and problems with species competition; thereby maintaining the biodiversity of the site. Ideally, transplants should be taken from sources as close as possible to the intended planting site, since minor genetic differences may alter a plants ability to withstand particular environmental conditions.

Under UK and European Legislation, the consent of the relevant countryside agency (e.g. English Nature, the Countryside Council for Wales and Scottish Natural Heritage) is required for the introduction of any species into designated sites. It is, therefore, advised that the relevant agency is consulted at an early stage.

Potential effects

Establishing saltmarsh on mudflats can reduce the area available to feeding birds and, where mudflat is a designated feature, this could be considered to represent a significant impact.

Monitoring

Measurement of the existing environment prior to selection of this technique, or the identification of suitable species, should include the following:

• Topographic contour mapping of the foreshore (marsh and mudflat) related to Ordnance Datum. The accuracy of topographic measurement should be better than ± 10mm and the contour map should include 100mm contour intervals.
• Measurement of the wave climate and tidal regime over a range of timescales, related to the elevation of proposed surface, with an indication of the number of inundations per year and duration of submergence.
• Recording of the elevation of plants on surrounding marsh surfaces, to enable plantings to be made at the correct height for the geographic location.
• Vegetation mapping of adjacent marshes, with a full species list, or the nearest marsh habitats (noting their distance away). This allows species suitable to the area to be selected.
• Measurement of the salinity of the flooding water and proposed planting substrate, including seasonal variations.
• Recording adjacent land uses which may cause disturbance to planted marshes, e.g. through flushing by pollutants or stock grazing.
• Measurement of the levels of pollutants and nutrients in the water and the proposed planting substrate to allow an assessment of potential mortality and/or the requirement for additional fertiliser or other soil amendments.

The future monitoring programme should be designed to assess the survival of the plantings, the need for further plantings and recommended changes to species types. It should also be possible to use the information gained from each scheme to plan and design future schemes. The information collected should, therefore, include:

• Percent survival rates of plants, plant vigour and vegetation cover, potentially using aerial photographs to assess spread of vegetation.
• Repeat vegetation mapping to assess change in diversity and to determine whether succession is occurring.
• Topographic contour mapping of the marsh and mudflat, related to Ordnance Datum, and vertical accretion measurements to assess whether the new marsh is accreting sediment.

Vegetation composition changes annually and, even if it is relatively stable, height and vigour can be highly variable from year to year. Measurements should, therefore, be repeated each year until a stable vegetation sward is established.

Locations

• Planting and sowing experiments, Tollesbury, Essex.
• Spartina anglica planting at Bosham, Chichester Harbour, West Sussex.
• Spartina anglica planting at Wytch Farm Gathering Station, Dorset.
• Spartina anglica planting using turfs at Cleaval Point, Poole Harbour, Dorset.
• Experimental realignment site at Abbotts Hall, Essex
• Saltmarsh restoration programme for pollution control and Spartina anglica transplanting, Southampton Water.
• Spartina anglica planting Humber Estuary Yorkshire.

Further information

For a more detailed assessment of vegetation planting the reader is referred to an Environment Agency study entitled “The restoration of vegetation on saltmarshes” (full reference provided below). The study considers seeding and planting issues, drawing upon experience both in the UK and abroad.

Brooke, J., Landin, M., Meakins, N. and Adnitt, C. (2000). The Restoration of Vegetation on Saltmarshes. Environment Agency R&D Technical Report W208.

Burd, F (1989a) The Saltmarsh Survey of Great Britain. NCC Research & Survey in Nature Conservation No. 17.