Calcareous grasslands occur on shallow chalk and limestone soils (pH 6.5-8.5). Former mineral workings can be ideal opportunities for creation. The precise composition of the vegetation community will depend on the climate, aspect and particular soil characteristics. It will take several years, once the grassland is established, for it to develop the full characteristics of the community.
High species diversity is encouraged by mineral nutrient stress and grazing, which prevent domination by a few aggressive species. Interesting communities develop by natural colonisation. It may be desirable to maintain some of these by rotational scraping of the substrate in a small-scale mosaic.
Topsoil is almost never needed - calcareous grasslands require substrate low in available nutrients to avoid competition from rank grasses. Instead, establish the habitat directly on the substrate. Note that for conservation, high productivity grassland is not desirable.
Natural colonisation of bare substrates will produce the most valuable grassland communities. Where a topsoil was retained, it can be replaced and prepared with agricultural techniques and machinery on slopes shallower than 20%. Chisel ploughs will break up compacted surface layers and stony ground.
Scarify the soil with disc harrows for natural regeneration, hay strewing or broadcast seeding.
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.
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 before continuing 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 lowland calcareous grassland previously and was properly conserved. This can be tested for.
Prevent rank grass species from suppressing the establishment of new species. Where such species 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. Natural regeneration on nutrient-poor soils produces sparse, diverse floras, so 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.
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 pre-seeding: 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 cheap and usually suitable technique, using 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.
Hydro-seeding where seeds and mulch are sprayed together, seeds areas normal techniques cannot reach, and unstable substrates. It requires expensive machinery and specialist contractors.
Use small machines (700-1,000 l) for seeding small areas (< 0.5 ha / day). Larger machines are capable of seeding up to 4 ha a day. Seeds are suspended in an aqueous mixture and can be sprayed up to 60 m from the machine.
Using container-grown plants and plugs
This is only applicable for introducing species such as orchids 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, and water in. Dib a hole the same shape as the plugs. Manage competing species by cutting them 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.
These are typically managed by grazing, which can be year round if at low stocking rates. However, stocking rates depend on sward productivity and are best prescribed locally - aim to produce a mosaic of tussocks and shorter turf.
Where grazing is not an option, or is insufficient, cutting and collecting the grass may be necessary. Do this after flowering in mid to late summer and remove from site, possibly using the material to extend the habitat elsewhere.
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.
Gilbert O L and Anderson, P (1998) Habitat Creation and Repair. Oxford University Press.
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.
Sward - above ground component of grassland
Rank - unmanaged, tall, closed sward grassland
Arisings - the products of management
Dib - creating 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