These habitats develop on land which is periodically flooded or waterlogged by fresh or brackish water, and where agricultural management– grazing, mowing or a combination – promotes vegetation dominated by lower-growing grasses, sedges and rushes.
Many grazing marsh grasslands derive from drainage of large wetland complexes. They are therefore associated with networks of drainage channels, which can have significant nature conservation interest, supporting diverse aquatic floras and invertebrate faunas. The biological interest of wet grasslands is further increased if they form part of a matrix of other wetland habitats, such as reedbeds and saltmarshes.
Design
Landforming should create conditions where the water-table is close to the surface for most of the year and splash or shallow flooding are possible during the winter months.
Avoid flat field topography; instead develop a mosaic of numerous small humps and hollows across each field. Varying micro-topography in this way creates conditions for very diverse swards to develop. It also benefits soil-dwelling invertebrates, that are themselves food for birds including breeding waders.
Avoid compaction when placing soil and especially when digging ditches; this can seriously affect the movement of water through the soil. In permeable soils, the water table may be controlled by adjusting the water level in the surrounding ditches and by ensuring that the ditches are closely spaced. In less permeable soils, foot drains and occasional surface inundation are necessary to manage soil wetness.
Hydrological regime requirements vary between different types of grazing marsh grassland. Inundation grassland types can tolerate flooding for long periods in the winter and occasionally in the spring and summer, whereas more species-rich wet grasslands will not tolerate prolonged flooding, particularly in the late spring and summer. Site-specific hydrological regimes should be developed with support from ecologists.
Size is an important consideration when designing grazing marsh grassland for breeding and wintering birds. They require large open areas, devoid of power lines, which can cause collisions or provide perches for predatory birds. Larger areas allow colonies of breeding waders to establish, which collectively may be more able to deter predators. This works best on sites greater than 100 ha, which can also be more cost-effective to manage.
Human disturbance should be kept to a minimum as this can significantly reduce use by wintering and breeding waterfowl. Blocks of at least 10 ha should be open, with no surrounding trees, tall shrubs or single trees, within or on the edges as this provides perching opportunities for crows and other predators.
Some birds, such as whinchats, short-eared owls and hen harriers, small mammals and some invertebrates, will benefit from less intensively managed swards of rank damp grassland. Cutting on rotation every three years encourages beneficial swards of this kind.
Establishment techniques
Soil preparation
Where topsoil exists, soil preparation can be undertaken with agricultural techniques and machinery. Chisel ploughs will break up compacted surface layers.
Scarify the soil with disc harrows for natural colonisation, hay strewing or broadcast seeding.
Natural colonisation
Natural colonisation is most likely to produce species-rich habitats appropriate to local conditions, and will be more natural than created grassland. If natural colonisation has started, assess its development, and if a good cover is establishing there is probably no need to continue with other methods.
Colonisation will usually succeed where a suitable seed bank is present, or existing suitable grassland is adjacent. A suitable seed bank may survive in the restoration topsoil if it supported the grassland type previously and was properly conserved. This can be tested for by growing samples under glass.
Prevent rank grass species from suppressing the establishment of new species. Where they occur, cutting and collecting, grazing or selective herbicides can be used. Early introduction of grazing, especially during the spring, has been shown to promote species diversity in new grasslands. On nutrient-poor soils, natural regeneration produces sparse but diverse floras, and may not require management for some time, especially if grazed by rabbits.
Any species ‘missing’ after several years that may be expected in a target habitat, can be selectively introduced (see below), but note that many species only colonise slowly under natural circumstances. Generally, natural colonisation should be left to develop by itself.
Seeding
Seeds may be collected from a local donor site using a brush harvester, or acquired from commercial sources – but if so, ensure the seeds have native provenance and are from a local source (see www.floralocale.org website). Only a restricted range of species is commercially available. These can be used as a starter sward as other species will colonise over time.
The following method should be used to introduce seeds:
- Use a moderately fine and firm seedbed
- Fertiliser is not required
- Control perennial weeds before they seed: let them germinate in spring / summer and treat with glyphosate
- Sow seed in September / October at 10-15 kg ha-1 depending on fertility and the urgency for green cover
- Encourage light at ground level by repeated cutting; this relieves competition for wildflower seedlings. Three cuts may be necessary on fertile soils, less or none at all on the poorest. Remove arisings.
Broadcasting is a cost effective method that uses conventional tractor-mounted spreaders. Mix with inert material such as sand to prevent seeds of different sizes sorting in the hopper. Broadcast by hand on small, steep or inaccessible areas.
Using container-grown plants and plugs
This is only applicable for introducing species such as orchids and snake’s-head fritillary that:
- do not grow easily from seed,
- spread vegetatively,
- and/or flower only after a number of years.
Plant out from September to mid-November or mid-February to early April on bare, or sparsely vegetated areas, in combination with seeding or to complement natural colonisation. Keep plugs moist, dib a hole the same shape as the plugs and water in. Manage competing species by cutting above the height of the inserted plants and removing cut material.
Appropriate planting density depends on a variety of factors, including the species ability to spread and the density of cover in the sward, and varies between 2 and 10 plants m-2. Planting at 3 plugs m-2 will cost in the region of £7,000 ha-1; container-grown stock is likely to cost 3 times more. Plantings of 5-10 species, planted in drifts covering 30-50% of an area will produce a natural effect if combined with seeding. Planting designs should reflect the natural distribution of species as much as possible.
Hay strewing
Hay that is cut and collected, with minimal turning, from local donor sites after flowering will contain seeds from many of the plants present. Most grassland species set seed between June and August. Cutting in early July should mean that most of the seeds are still attached. A second cut would catch later seeding species. Actual timing of cuts will depend on location and species composition.
More seed may be lost when collecting using a forage harvester than with hay making, but the choice of method will depend on the availability of machinery.
The hay should be spread as soon as possible after its collection to minimise seed loss during storage through composting or rot
Long-term management of grazing marsh grassland
Grazing marsh grasslands are typically managed by summer grazing and hay cropping. Undertaking grazing at low stocking levels avoids trampling of birds nests and maintains a structured sward. Stocking rates depend on sward productivity and are best prescribed locally. Livestock should be removed in winter when water levels are high. Where early summer grazing isn’t available, cut hay after flowering has finished, and turn livestock out afterwards the graze the aftermath; the short turf will favour geese and ducks in winter.
Further Reading
Crofts, A and Jefferson, R G (eds) (1999) The Lowland Grassland Management Handbook. 2nd Edition. English Nature/The Wildlife Trusts, Peterborough.
Davis, B N K (ed) (1982a) The ecology of quarries. The importance of natural vegetation. Institute for Terrestrial Ecology, Cambridge.
Walker, K J, Manchester, S J, Mountford, J O, Stevens, P A and Pywell, R F (2001) Methodology for restoring and re-creating semi-natural lowland grassland. A review and quantitative model. CCW Contract Science Report No 437.
Wells, T, Bell, S and Frost, A (1981) Creating attractive grasslands using native species. Nature Conservancy Council, Peterborough.
Glossary
Sward - The above ground component of grassland
Rank - Unmanaged, tall, closed sward grassland
Splash (shallow) flooding - Shallow flooding from 0 to between 5-10cm
Foot drain - Small ditch that assists water distribution
Arisings - The products of management
Dib - To create a small hole in the ground to receive a plant plug
Relevant case study
The information set out within this advisory sheet in no way constitutes legal or regulatory advice and is based on circumstances and facts as they existed at the time Nature After Minerals compiled this document. Should there be a change in circumstances or facts, then this may adversely affect any recommendations, opinions or findings contained within this document