Acid grassland habitat audit

Acid grassland generally consists of fine-leaved grasses such as common bent and fescues, with typical herbs such as sheep's sorrel, tormentil and heath bedstraw. Acid grassland flora is sometimes associated with lowland heath and mire communities. This assemblage is commonly found on nutrient-poor, free-draining and acidic soils underlain by the sands of bagshot beds, gravels, sandstones and acid igneous rocks.

Although acid grassland is one of the most extensive semi-natural habitats in the United Kingdom, there are scant data on its true extent. Estimates suggest that there is in excess of 1,200,000 ha of acid grassland in the uplands but in the lowlands there is unlikely to be more than 30,000ha. Acid grassland is widespread throughout London; only six out of the thirty-three London boroughs have no recorded areas of acid grassland. There are several quite extensive areas, particularly in the Royal Parks in west London, the southern part of Epping Forest in north London and Wimbledon Common.

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.

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.