Jncc coastal Directories Project Region 11 The Western Approaches

Grazing is probably the oldest form of saltmarsh
management; in this region many of the saltmarshes are
grazed, including most in Bridgwater Bay and the Severn
Estuary.  Figures for stocking densities range from one to six
animals per hectare, with grazing usually taking place from
May to September.
Spartina was planted in the Severn from 1913 onwards
and spread rapidly, particularly in the 1950s and 1960s.
However, since the 1970s the extent of Spartina marsh has
declined, owing to both erosion of the low marsh and
replacement by other species (Dent 1987; Ranwell 1961,
1964a, b; Willis 1990).  The spread of Spartina, therefore,
caused only a temporary aberration in the long-term trend
of saltmarsh loss in the Severn. 
3.6.4  Information sources used
Saltmarshes in Devon, Cornwall and River Ogmore were
surveyed in 1982 as part of the NCC’s national saltmarsh
survey; detailed reports are available and the results are
summarised in Burd (1989a-d).  Data presented here are
derived from that database.  The national saltmarsh survey
provided an intermediate level of detail between Phase 1
habitat survey and the National Vegetation Classification
(NVC: Rodwell in prep.).  It did not include all areas of
transition to other habitats such as sand dune, shingle and
freshwater marsh.  Saltmarsh vegetation in non-tidal
marshes or behind permeable barriers, as at Porlock Marsh,
and areas of eelgrass were not recorded.  Some small sites,
such as the River Kenfig and the Isles of Scilly, were not
covered by the national survey.  
For the Severn (including Bridgwater Bay and East
Aberthaw), the national survey used the results of earlier
work by Smith (1979).  As the Severn data are now quite old
and there were some difficulties in fitting them into the
categories used by the national survey, they must be treated
with more caution than data for other parts of the coastline.   
The history and development of the Severn saltmarshes
have been studied in detail by Allen (summarised in Allen
(1992)).  Several vegetation surveys of saltmarshes in the
Severn Estuary were carried out as part of feasibility studies
for barrages.  The study by Dent (1987) provides vegetation
descriptions and maps for the saltmarshes between Cardiff
and Newport and includes a comparison of recent and
historic maps and aerial photographs.  Teverson (1981) gives
an account of the Severn saltmarshes as a whole, plus
detailed descriptions, histories and marsh profiles for four
case study sites.  Gray et al. (1989) used levelled line
transects (including several sites in the Severn) to draw
conclusions about the niche of Spartina. 
Saltmarsh surveys have also been carried out for other
development proposals and are reported in the
Environmental Statements, as for example, for the Severn at
Caldicot (Environmental Advisory Unit 1991) and at
Rhymney (SGS Environment 1995).  The extent and vigour
of the Zostera bed in the Severn Estuary are being monitored
in connection with the construction of the second Severn
crossing. 
Studies of saltmarsh succession in Bridgwater Bay are
reported by Ranwell (1961, 1964a, b) and Willis (1990).  
The history and extent of Spartina anglica in the Severn is
summarised by Martin (1990) and the distribution of
Spartina species, including the infertile hybrid Spartina
townsendii, by Holland (1981).  An account of the
invertebrate fauna of a saltmarsh in the Severn is provided
by Little (1990).  
3.6.5  Acknowledgements
Staff of English Nature and the Countryside Council for
Wales kindly provided information and reference material. 
3.6.6  Further sources of information
A.  References cited 
Allen, J.R.L.  1992.  Tidally influenced marshes in the Severn
Estuary, southwest Britain.  In: Saltmarshes: morphodynamics,
conservation and engineering significance, ed. by J.R.L. Allen &
K. Pye, 123-147.  Cambridge, Cambridge University Press. 
Burd, F.  1989a.  The saltmarsh survey of Great Britain. Peterborough,
Nature Conservancy Council.  (Research & survey in nature
conservation, No. 17.)
Burd, F.  1989b.  Saltmarsh survey of Great Britain.  Regional
Supplement No. 2.  West Midlands. Peterborough, Nature
Conservancy Council.  
Burd, F.  1989c.  Saltmarsh survey of Great Britain.  Regional
Supplement No. 3.  South West England. Peterborough, Nature
Conservancy Council.  
Burd, F.  1989d.  Saltmarsh survey of Great Britain.  Regional
Supplement No. 11.  South Wales. Peterborough, Nature
Conservancy Council.  
Dent, S.  1987.  The current status and recent history of Spartina anglica
in the Severn Estuary between Newport and Cardiff.  Peterborough,
Nature Conservancy Council. 
Environmental Advisory Unit.  1991.  The Second Severn Crossing -
effects on estuary ecology and fisheries.  London, Severn Bridges
Bill Parliamentary Session 1990/91.  Study report SR4.  
Fox, A.D., & Salmon, D.G.  1988.  Shelducks on the Severn Estuary.
Report to the Department of Energy.  (Severn Tidal Power
Report No. SBP 40.)
Gray, A.J., Clarke, R.T., Warman, E.A., & Johnson, P.J.  1989.
Spartina niche model.  Prediction of marginal vegetation in a post-
barrage environment.  Harwell, ETSU.  (Energy Technology
Research Unit Report ETSU-TID-4070.)
Holland, S.C.  1981.  Spartina of the Severn Estuary.  Gloucestershire
Naturalists’ Society Journal, 32(3) Supplement: 1-8. 
Little, C.M.  1990.  Animals of the Severn Estuary saltmarshes.
Proceedings of the Bristol Naturalists’ Society, 50: 83-94.
Martin, M.H.  1990.  A history of Spartina on the Avon coast.
Proceedings of the Bristol Naturalists’ Society, 50: 47-56.
Pye, K., & French, P.W.  1993.  Erosion and accretion processes on
British saltmarshes.  London, Ministry of Agriculture, Fisheries
and Food. 
Ranwell, D.S.  1961.  Spartina marshes in southern England.  I.  The
effects of sheep grazing at the upper limits of Spartina marsh in
Bridgwater Bay.  Journal of Ecology, 49: 325-340.
Ranwell, D.S.  1964a.  Spartina marshes in southern England.  II.
Rate and seasonal pattern of sediment accretion.  Journal of
Ecology, 52: 79-95.
Ranwell, D.S.  1964b.  Spartina marshes in southern England.  III.
Rates of establishment, succession and nutrient supply at
Bridgwater Bay, Somerset.  Journal of Ecology, 52: 95-105. 
Rodwell, J.S., ed.  In prep.  British plant communities.  Volume 5:
Maritime and weed communities.  Cambridge, Cambridge
University Press.  
SGS Environment.  1995.  Lamby Way proposed landfill development.
Environmental statement. Cardiff, City of Cardiff.
Region 11  Chapter 3  Terrestrial coastal habitats
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