Acid Grassland Habitat Audit - page 2
Nature Conservation Importance, Threats and Opportunities, Data Sources, Rationale and Limitations of Approach
Nature Conservation Importance
Lowland acid grassland is becoming increasingly rare in Britain. Although intrinsically less species-rich than neutral or chalk grassland of similar quality, acid grassland contains many characteristic species that do not occur widely in other grassland types. Nationally rare plants such as clustered clover Trifolium glomeratum, fine-leaved sandwort Minuartia hybrida and autumn squill Scilla autumnalis can all be found in acid grassland in London. Even within central London, in the City of Westminster, a tiny patch of acid grassland supports harebell Campanula rotundifolia. More typical acid grassland species include mat grass Nardus stricta, early hair-grass Aira praecox and sheep’s sorrel Rumex acetosella.
Acid grasslands are also valuable for invertebrates, especially hymenoptera (ants, bees and wasps) such as the mining bee Andrena florea; and butterflies such as green hairstreak and small copper. Few bird species have a particular association with acid grasslands, but green woodpecker, meadow pipit and linnet are invariably present on the larger acid grassland sites.
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Some acid grassland sites of nature conservation value in Greater LondonHounslow Heath, LB Hounslow |
Threats and Opportunities
Threats
Lowland acid grassland is declining nationally. It is likely that the
area has declined greatly within London with the loss of traditional management
practices affecting core areas such as commons and heaths. The current threats
to this habitat include:
 | Loss of habitat through cessation of traditional management, especially grazing, causing encroachment by trees and scrub. |
| Damage and erosion caused by increasing recreational pressure. |
| Fragmentation and isolation of the remaining habitat. |
| Direct loss of habitat due to ‘improvement’ of grassland for amenity purposes e.g. mowing and/or fertiliser application to produce a sward suitable for golf course fairways or sports pitches. |
Opportunities
Although much reduced in area and distribution and varying in quality, acid
grassland is still a significant habitat in Greater London, particularly in the
many parks and commons. It is, however, a fragile habitat which requires careful
management. Many formal parks and open spaces contain areas of acid grassland
and relaxation of the mowing regime in these areas will quite quickly result in
some enhancement of biodiversity – common blue, small heath and small copper
butterflies could be encouraged to breed, for example. A considerable amount of
acid grassland also occurs on some of London’s older golf courses and a
similar programme of identifying key areas and modifying mowing regimes could
result in considerable benefit to biodiversity without seriously detracting from
the primary purpose of the course.
Opportunities should be sought to enhance existing extensive areas of acid grassland through methods such as scrub clearance and the re-introduction of grazing. This should be carried out only after careful consideration of the value of alternative management options; some areas might be suitable for restoration to heathland and in other areas a scrub/grassland mosaic may be especially valuable for certain species of bird and invertebrate. Mowing may be the only practical management regime for most acid grassland.
Where recreational pressure is resulting in loss or damage to important acid grassland habitat, visitor management should be implemented in combination with a programme to raise awareness of the value of acid grassland sites. Erosion caused by recreational use of acid grasslands can, in some instances, be of benefit, creating bare areas which are favoured by some acid grassland invertebrates, particularly those that require exposed ground in which they can burrow.
Data Sources
Archer, J. & Curson D. (1993). Nature Conservation in Richmond upon
Thames. London Ecology Unit.
Archer, J. & Robinson P. (1994). Royal Borough of Kensington and
Chelsea. Borough Ecological Survey. London Ecology Unit.
Archer, J. Dawson, & D. Hewlett, J. (1995). City of Westminster
Nature Conservation Survey. London Ecology Unit.
HMSO (1995). Biodiversity: The UK Steering Group Report. Volume 2 Action
Plans. London HMSO.
London Ecology Unit, (1989). Islington Wildlife Survey. London
Ecology Unit.
London Ecology Unit, (1997). Redbridge Habitat Survey. London
Ecology Unit.
London Wildlife Habitat Survey (1984/5). Held by LEU, includes habitat dot
distribution maps, aggregated area figures and standardised information on
every survey parcel.
Wicks, D & Cloughley, P (Eds) (1998). The Biodiversity of Southeast
England: An Audit and Assessment. Hampshire and Isle of Wight Wildlife
Trust.
Rationale and limitations of approach
Data were taken from the London Wildlife Habitat Survey (1984/85) and selected re-surveys of individual boroughs. The choice of data used reflects both data availability and time constraints. The following re-survey data was used: Kensington and Chelsea (1994) Islington (1989) Westminster (1995) and Redbridge (1997).
It is likely that acid grassland is under-recorded owing to difficulties in locating all examples of this habitat. Furthermore, much acid grassland in heathland landscapes may have been recorded as heath.