Heathland sites in SurreyIn Surrey, heathland is largely confined to two Natural Areas: the London Basin (on Tertiary sands and gravels overlying the London Clay) in the north west of the county and the Wealden Greensand in the south west and centre. Additionally, there is some heathland (notably Headley Heath) on superficial gravels overlying the chalk in the North Downs Natural Area.
a) London Basin Natural Area
Along with contiguous heathland in Hampshire and Berkshire, heathland in this part of Surrey is generally referred to as belonging to the ‘Thames Basin’ rather than ‘London Basin’. Approximately two thirds (about 2,000 hectares) of the county’s surviving heathland lies in the Thames Basin, forming a discontinuous band of sites from Epsom, Esher and Oxshott Commons in the east, westwards to the Hampshire border. Heathland has developed here on the Bagshot, Barton and Bracklesham Beds, Tertiary deposits mostly of sands and gravels with some clays. The topography of these heaths is generally gentle and there are large areas of low lying land supporting humid and wet heathland although, in places, steep hills support dry heath. Three sites, Ash Ranges, Pirbright Ranges and Chobham Common, account for three quarters of the heathland in the Thames Basin; nevertheless other smaller sites have considerable importance in maintaining biodiversity across the range of heathland within the Natural Area.
b) Wealden Greensand Natural Area
Heathland on the Wealden Greensand makes up one third (about 1,000 hectares) of the county’s heathland, and forms part of a larger area extending into Hampshire and West Sussex. With the notable exception of Thursley NNR and its environs (which supports an internationally important mire), the Wealden Greensand heaths are predominantly dry sites, lying on the Folkestone, Sandgate and Hythe Beds of the Lower Greensand. The topography of these heaths, especially in the south west of the area, is more varied than in the Thames Basin – higher ground often rising steeply and forming a deeply incised landscape as at the Devil’s Punch Bowl. The bulk of the surviving heathland is centred on or close to Thursley, Hankley and Frensham Commons with Blackheath an important outlier to the north east. Fragments of heathland at higher altitude and of different character persist further east at Leith Hill and on the Hurtwood in the characteristic ‘Surrey Hills’ landscape, now heavily wooded.
c) North Downs Natural Area
In a very few places, superficial deposits over the chalk of the North Downs support heathland. The largest example is Headley Heath where the more ‘typical’ acidic heathland plant communities are accompanied by small areas of ‘chalk heath’ that are interesting mixtures of chalk downland and heathland species. There are probably no more than 20 hectares of heathland over the chalk.