|
INTRODUCTION TO GRAZING MARSH
Definitions and descriptions
Grazing marsh is a term used to describe permanent pasture used for grazing
or hay-making. Unlike the other coastal habitats dealt with in this guide, it
is has been created and is maintained by human use. It originates from saltmarsh
or other tidal wetland, separated from the influence of the tide, typically
by a linear earth sea bank or sea wall. Subsequent drainage and low intensity
agriculture facilitates the development of a distinct nature conservation value.
Three variations can be identified which fall under the general category of
Coastal
and Floodplain grazing marsh, namely:
- Coastal
grazing marsh, derived from the enclosure of saltmarsh
- a distinctly maritime habitat;
- Coastal
wet grassland, derived from tidal brackish swamps - some saline
influence;
- Lowland
wet grassland near the sea but derived from non-tidal wetlands
- no saline influence.
The typical coastal grazing marsh and coastal wet grassland referred to above
includes a number of different habitats, with modified forms of saltmarsh creeks,
saline seepage areas and grazing pasture prominent. These in their turn support
a wide diversity of plants and animals. Areas of grazing marsh provide breeding
sites for a variety of ground-nesting birds. In the winter they can support
large numbers of migratory birds which use them for feeding and roosting. Salinity
gradients in the drainage ditches can be especially valuable for some rare invertebrates.
Coastal wet grassland lacks the features associated with saltmarsh (especially
tidal creeks).
Grazing marshes occurs extensively in low-lying areas around the coast of the
UK . Coastal grazing marsh is the predominant type dealt with in the Guide.
These overlap with coastal wet grasslands and at some sites it is difficult
to distinguish between the two, as they form a continuum in many areas. They
tend to be located in and around major estuaries and are found in almost all
the CHaMPs,
occurring as a major component of some.
Traditional management
Traditional
management typically involves low intensity grazing and fluctuating
water levels are the key to maintenance of the nature conservation value of
most grazing marshes. Low input of fertilisers, pesticides and herbicides are
characteristic of the best areas. It is important to recognise that the nature
conservation interest co-exists with traditional agricultural use and is to
a large extent dependent on it. Hydrological regimes which favour both high
winter and summer water levels provide good opportunities for wintering and
breeding birds respectively. Salinity gradients are influenced by freshwater
flows and/or seepage through sea banks.
Pressures
In the last 40 years or so the major losses
have resulted from the combined effects of drainage
and intensive arable cultivation, which have reduced the total area of the habitat
considerably. The desire to intensify agricultural use by increasing stock
levels has led to the manipulation of water levels, particularly
to reduce flooding in winter. The overall effect is to reduce the diversity
of plants species and make the habitat less suitable for breeding and wintering
birds. Increased use of fertiliser can also lead to eutrophication, especially
within the ditches, with a potentially adverse impact on water plants and invertebrates.
States and values
The key element causing change is the degree of intensification of agricultural
use of the grazing marsh. Three
states have been identified, having relevance to any restoration
strategy for this habitat, namely:
- State
1 - Low intensity, traditional management;
- State
2 - 'Improved' grazing, extended grazing grazing regimes;
- State
3 - Intensive agriculture, usually for arable crops.
As agricultural use intensifies the value for wildlife decreases this is particularly
the case where arable crops are grown. Restoring grazing marsh and its associated
biological interest (including that expressed by the targets
in the UK Biodiversity Action Plan for this habitat) is a primary reason to
restore this habitat.
Guidance (routes to restoration)
The route
to restoration for coastal grazing marsh and coastal wet grassland
can be achieved by reversing the process of agricultural intensification. Manipulation
of hydrological regimes and reducing grazing levels i.e. moving from State
2 to State 1 and thus reinstating a more traditional management,
is the primary focus (see for example Holkham,
NNR, North Norfolk). This is a relatively easy task where improving or restoring
ornithological interests is a priority. Restoring
plant (and animal) diversity in the grasslands and associated habitats
and reaching the Biodiversity
Action Plan targets for this habitat is more problematic.
The most extreme form of habitat re-creation is the creation of grazing marsh
from arable land. This is an important issue not only in its own right, but
also for managed
realignment. Here re-creating such areas will be required if the
full range of habitats from intertidal flats to saltmarsh and grazing marsh
is to be attained where such schemes are attempted. Thus moving directly from
State
3 to State 1 or via State 2 could fulfill this role. There are examples
of this approach on the North
Kent Marshes.
Key Publications
- Background documents - A general description of the habitat (Gray
1977);
- Restoration guides - There are a number of key publications covering
all aspects of re-creating, restoring or creating wet grasslands. None of
these are specifically targeted at the coastal grazing marsh and coastal wet
grassland, which are the subject of this guide, but all provide valuable material.
Especially significant is the Wildlife Trust's wetland
restoration manual. Also valuable are the various publications
produced by the Royal Society for the Protection of Birds (Benstead
et al. 1997; Benstead et al. 1999;
Brooks & Agate 1997; Treweek
1991). The RSPB have also produced a number of Reserve Management Information
sheets which provide a summary of key points in relation to "Managing
water levels on wetlands" RSPB 1;
"Re-establishing wet grassland" RSPB
2; "Management of wetland sites for breeding waders" RSPB
3. ;
- Web sites - The Wildlife Trusts (www.wlt.org.uk)
. The RSPB (www.rspb.org.uk)
is especially useful as a source of reference including the summary documents
listed above. Most of these can be downloaded from their site via the sections
on reserve management.
Key References
Benstead, P., Drake, M., Jose, P.V., Mountford, O., Newbold, C. & Treweek, J.
1997.
The Wet Grassland Guide: Managing floodplain and Coastal Wet Grasslands for Wildlife.
RSPB, Sandy.
Benstead, P., Jose, P.V., Joyce, C.B. & Wade, P.M.
1999.
European Wet Grassland: Guidelines for Management and Restoration. RSPB, Sandy.
Brooks, A. & Agate, E.
1997.
Sand Dunes: A Practical Handbook, Third Addition.
British Trust for Conservation Volunteers, Wallingford.
RSPB 1
Manageing Water Levels on Wetlands.
Reserve Management Information sheets
Royal Society for the Protection of Birds.
RSPB 2
Re-establishing Wet Grassland.
Reserve Management Information sheets
Roal Society for the Protection of Birds.
RSPB 3
Management of Wet Grassland for Breeding Waders.
Reserve Management Information sheets
Royal Society for the Protection of Birds.
Treweek, J.
1991.
Wetland Restoration: Techniques for an Integrated Approach.
ITE/MAFF.
References
Gray, A.J.
1977.
Reclaimed land.
In: The Coastline, ed.Barnes, R.S.K.John Wiley & Sons, Chichester, 253-270.
|
