129 - Thames Basin Heaths : Description

Physical and functional links to other National Character Areas

The Thames Basin Heaths National Character Area (NCA) lies in the London Basin, one of several NCAs lying within this syncline. The axis of the fold runs east-west – passing through this NCA – from the Berkshire and Marlborough Downs NCA to the Essex coast. The high rim of the London Basin is found to the west and south, where vantage points in the North Downs NCA and Hampshire Downs NCA, for example, offer views of the lower-lying Thames Basin Heaths NCA. The Chalk landscapes in the west extend from this NCA into the Berkshire and Marlborough Downs NCA and Hampshire Downs NCA, and this wider Chalk landscape is designated as the North Wessex Downs Area of Outstanding Natural Beauty (AONB).

The Thames river system drains this basin, with major tributaries flowing through the Thames Basin Heaths NCA from the Berkshire and Marlborough Downs NCA in the west, and from the Hampshire Downs NCA, Thames Basin Lowlands NCA and other NCAs to the south. Engineered surface and groundwater supply links also exist with surrounding NCAs: the chalk aquifers in the neighbouring North Downs NCA, Hampshire Down NCA and Berkshire and Marlborough Downs NCA are notable sources of water. The Basingstoke, Wey Navigation, and Kennet and Avon canals provide a corridor for transport, recreation and wildlife – including otter, water vole, fish, and non-native species such as Himalayan balsam and American signal crayfish.

Birds make use of complexes of sites straddling the NCA boundaries. Large numbers of waterfowl (such as gadwall) flock around the South West London Waterbodies Special Protection Area (SPA) and Ramsar site to roost and feed in the winter. Breeding Dartford warbler, nightjar and woodlark use habitat mosaics across the Thames Basin Heaths SPA.

Transport links within this NCA include the M3, M4 and M25 motorways, as well as numerous A roads and railways linking to the wider South East and London. These all make the green spaces of the Thames Basin Heaths NCA accessible to people from numerous major settlements in nearby NCAs – including Basingstoke, Reading, Staines, Guildford and west London. Virginia Water and Chobham Common are large green spaces near to west London and just off the M3.

Distinct areas

• Blackwater Valley

The Thames Basin Heaths today

The Thames Basin Heaths NCA drops in altitude eastwards, into the London Basin. The Thames flood plain at Weybridge lies at below 40 m above ordnance datum (AOD) in the far east, just inside the M25 in west London. The Thames is met by the rivers Wey and Mole flowing from the south, while a network of small streams drains the low, relatively rural area around Chobham, within the London greenbelt. The Wey Navigation and Basingstoke canals provide key recreation corridors, incorporating flood plain habitats and historic features (including mills).

Heading west, the ground rises onto one of several plateaux found across this NCA. Historic monuments – including numerous prehistoric barrows and hill forts, such as the barrow cemetery and Caesar’s Camp near Aldershot – are found on plateau vantage points. The plateaux comprise Tertiary sands and gravels, which give rise to acid, freely draining and light soils favoured by heather, gorse, bracken, oak and birch. Open heathland has decreased significantly over the last century as a result of scrub and secondary woodland encroachment, and conifer plantations. There is a variety of colour in autumn: the heathers flower in purple, while the broadleaved trees and bracken turn yellow, red and brown. Plantations of evergreens provide year-round colour and shelter. Further diversity is provided by acid grassland and wet conditions, giving rise to bog, wet heathland, streams and ponds. Dragonflies, such as the rare brilliant emerald and the ruddy darter, hunt around the heaths and woods. Farmland is minimal, as soils are poor for any use other than rough pasture. Across the NCA, Grade 1 and 2 soils account for only 6,600 ha; Grade 3 soils make up 40 per cent of the area (47,700 ha).

Major river valleys cut down to the London Clay to define a large eastern plateau and several smaller plateaux in the west. Into these main valleys, minor streams drain off the plateau slopes – often in steep ‘gulleys’ which, in places such as Greenham Common, support wet alder woodland and county rarities. The Loddon – and its tributaries the Blackwater, Whitewater and Hart – drains the central area, while the Kennet and its tributaries (including the Enborne) flow in the east. The wide clay flood plains support mixed agriculture, while the localised fertile soils based on alluvium are cultivated or provide lush pasture. A few neutral grassland meadows remain, such as Briff Lane Meadows Site of Special Scientific Interest (SSSI), and Stanford End Mill and River Loddon SSSI. Historic mills survive in places along the rivers. Ecologically rich wet woodland, reedbed, marsh and ditches are found in the NCA; these are most extensive in the Kennet Valley, where Thatcham Reedbeds SSSI is the largest inland reedbed complex in southern England. Several sites supporting Desmoulin’s whorl snail are conserved as part of the Kennet and Lambourn Flood Plain SAC. The Blackwater, coursing over alluvial and Tertiary deposits, is surrounded by urban development for much of its length; associated with this, much of its channel is engineered and high phosphate levels have been recorded. However, a narrow corridor incorporates a string of wet alder woodlands, marsh and wet acid grasslands in the Blackwater Valley SSSI. Wet acid habitats are also found in the Hart catchment.

Aggregate extraction takes place along both the Kennet and Blackwater and is distributed across England. Old workings have been restored to include open water and reedbed, with some lakes managed for angling and watersports.

In the far west, the upper reaches of the Kennet (and also the Lambourn and Pang) cut down to the Chalk of the Berkshire and Marlborough Downs dip slope. The chalk of the Hampshire Downs in the south gives rise to springs at the foot of a north-facing escarpment rising up to 297 m at Walbury Hill. Along this escarpment, there are species-rich chalk grasslands, hanging woodlands, parklands, historic monuments and springline villages such as Kingsclere. These downland areas are designated as nationally significant landscapes as part of the North Wessex Downs AONB.

Farmsteads and villages are densely scattered across the western plateaux and valleys, and major settlement is restricted to Newbury and Thatcham – from which major A roads radiate. Winding lanes traverse an enclosed countryside of small-scale patchworks of hedged fields, often with oak trees and woodlands. Typically, the woods are small, with semi-natural oak and birch on ancient sites: Pamber Forest is the largest example, but there is also a rich concentration in the Pang Valley. There are relatively large conifer plantations on former heathland and common on the plateau around Mortimer. There are public rights of way across farmland and numerous commons near to settlements, including large heathlands and woods at Greenham, Snelsmore and Newtown. Commoners rarely practise their rights, and so management falls to landowners and conservation organisations.

In contrast to the west, the east comprises considerable modern development juxtaposed with undulating expanses of heathland, woodland and plantations. Non-native trees and rhododendron are distinctive in this area. Three large heathland and woodland SSSI – averaging nearly 1,500 ha each – dominate the countryside. This core of semi-natural habitat is significant, considering the area’s proximity to London, and the density of settlement and predominance of agriculture in south-east England. Internationally important populations of woodlark, nightjar and Dartford warbler breed in the area. Their habitat is protected by the Thames Basin Heaths SPA, which covers 13 sites.

Public access to large areas of heathland and plantation around Camberley is permissive, and is subject to Ministry of Defence requirements. In contrast, in places such as Bracknell Forest and on smaller historic commons, visitors are encouraged by car parks, signage and education. Chobham Common covers 513 ha, and is the largest NNR in the south-east. Such areas offer experiences of farreaching views, nature and tranquillity.

Such recreational opportunities are available to a large local population, but visitors need to be managed in order to avoid disturbing breeding birds (such as woodlark), and problems such as arson and vandalism. Large and dense conurbations (including Aldershot, Farnborough, Camberley and Sandhurst) merge along the Blackwater and M3, lying just outside the London greenbelt.

Within the greenbelt, low-density housing – such as at Sunninghill – is characterised by large gardens. Settlements are inter-connected and linked to London by the M3 and by numerous, typically straight A roads that dissect the areas of heathland and woodland. Roads and settlements are usually enclosed by tree belts or woodland, while rhododendron is a frequent non-native. Leisure land uses are dominant near to settlements, and include horse paddocks, country parks, garden centres, ‘hobby farms’ and golf courses – including championship venues such as Wentworth. Mansions and the grounds of large, historic estates create a sense of prestige across the NCA, and include well-known names such as Virginia Water and Highclere Castle – both of which are open to the public. These parklands contain veteran trees and remnant wood pasture from the historic royal forests.

The landscape through time

The oldest exposed rock in the Thames Basin Heaths NCA is the Chalk, which was deposited in tropical seas during the Cretaceous Period 95 to 65 million years ago. In the subsequent Tertiary Era (64 to 2 million years ago), a series of sands and mudstones were deposited on the Chalk. The Reading Beds are the oldest surviving sediments from the Tertiary in this NCA, and were deposited by ancient river systems. The London Clay was laid down when the London Basin was flooded by the sea. The youngest Tertiary sediments are the Bagshot, Barton and Bracklesham Beds, lying at the top of the succession. Around 40 million years ago, the Chalk was also subject to massive earth movements; these folded the bedrock to create the syncline or depressed area of the London Basin. During the Quaternary, rivers cut down into the Tertiary sediments to create valleys and deposited material over the last two million years. Heather grew among the tundra vegetation.

The Thames and its tributaries were a focus for prehistoric humans, with a move into upper valleys and downland occurring later. Stone tools suggest that humans were present around 500,000 years ago. Neolithic and bronze-age barrows and iron-age hill forts are found at vantage points across the area, and flint artefacts have also been found.

Many prehistoric monuments lie in a heathland setting, which itself originated in prehistory. Heathland evolved following woodland clearances, carried out by humans to attract grazing animals and allow cultivation. The freely draining soils, being exposed to the leaching effects of rain, became increasingly acidic, developed iron pans and generally declined in fertility. The marginal agricultural potential of these soils has since shaped its land use. Heathers dominate on these soils, and trees such as birch and oak grow where they have not been checked by either grazing animals or human intervention. By the end of the 1st century AD, the civitas capital of Calleva Atrebatum (near the modern town of Silchester) had been established. Roman roads radiated out from Calleva, and there were Roman villas and farmsteads across the area. A local tile industry exploited the clay. Grim’s Ditch, a linear earthwork running along the higher ground between Calleva and the River Kennet, suggests that there were attempts to define and protect the territory, but the settlement had become marginalised by the 5th century.

Piecemeal woodland clearance produced small, irregularly shaped fields or assarts for farming. Farms were small and scattered across these agriculturally poor soils, giving rise to a high density of farmsteads. Where soils were difficult to cultivate – such as on the clays in north Hampshire – woodland was retained and managed for timber, coppice products and wood pasture under a similar economy to that of the New Forest. Coppicing and other woodland activities were undertaken to supplement farming, and many woods remain today (as ancient woodland sites).

The mosaic of heathland, woodland, wetland and grassland was ideal for hunting and, following the Norman conquest, areas around Pamber, Eversley and Bagshot were designated as ‘royal forest’, discouraging settlement. Windsor Forest also lies nearby, to the north-east. These royal parks later evolved into large parks and estates, including Stratfield Saye, Dogmersfield and The Vyne. The area covered by historic parkland in this NCA used to be nationally significant (7 per cent of the NCA in 1918), but by 1995 it had halved due to conversion to arable and other land uses.

The medieval market towns providing for the dispersed farms and hamlets included Newbury, Odiham, Kingsclere and Reading. Some developed from Saxon royal estate centres, while others (such as Newbury) were planned ‘new towns’.

Settlements developed around commons from the 16th century onwards. Commoners would have used the common for grazing animals, coppicing trees for firewood, digging sand and clay for brick making, and so on. Other than the farmstead, relatively few early buildings survive; by their nature, they were usually small and poorly built, and so were likely to be replaced over time. Excavation pits and tracks are still evident today.

By the 18th and 19th centuries, most buildings were constructed using brick and tile made by the flourishing local industry. Earlier timber frames were often encased or fronted with brick. There are some important examples of 16th- and 17th-century brick barns in this NCA.

Historically, farming followed a sheep-corn system, but arable production was restricted to the valley floors, such as along the Loddon and Foudry. In the east, mutton and lambs were supplied to London markets rather than wool. Livestock farming involved rough grazing on heathland and other rough pastures, while cattle were grazed on the fertile but wet pastures of the Kennet Valley for fattening and dairy. There were water meadows and mills along rivers such as the Kennet and Wey. Over time, agricultural production drove the re-organisation of field boundaries and enclosure, although historic field systems do remain in places. Original assarts were, in most cases, re-organised; where soils were suitable for arable, fields were enclosed to create medium-sized spaces. There were few open fields to be enclosed by Parliamentary Enclosure Acts in this NCA.

Trade links with London and other markets strengthened on the opening of the River Wey Navigation in 1653. This preceded the so-called Canal Age by 100 years, with the Kennet and Avon Canal and Basingstoke Canal both coming later.

As livestock grazing on heathland areas declined, other uses for them were being sought. Up to the 18th century, this marginal land constituted one of the largest and most continuous areas of lowland heathland in England. The uninhabited, undulating heathland areas have long attracted military uses. The large bases of Aldershot and Farnborough, in the east, have their origins in early military camps, while Greenham and Aldermaston, in the west, were 20th-century wartime airfields. Forces land uses have prevented urban development on large areas of heathland and woodland.

Other changes of use led to fragmentation and a reduction in area of unenclosed heathland. Large blocks of conifers were planted for timber production and, in the east, the acid soils attracted commercial nurseries specialising in rhododendron. In the 19th century large estates enclosed heathland to be managed as farmland. The rapid growth of London – and heathland’s perceived scenic qualities – gave rise to residential development in the east from the 18th century onwards. Park estates, modest country houses and villages grew up, as well as golf courses. Since the mid-19th century, residential development has been intensive in the east, creating large towns such as Ascot, Camberley, Farnborough and Woking.

In the east, the particular focus for development continues to the present day, and construction has been driving almost continuous mineral extraction in the (Kennet and Blackwater Valleys). Neglect of traditional features such as boundaries, pasture and historic farm buildings was evident in the 1990s. The designation of the Thames Basin Heaths SPA in 2005 has stimulated the creation of new public green spaces, and the improvement of visitor management in the SPA and surrounding area. In recent years, landowners (including the Ministry of Defence) have carried out conservation management of heathland and woodland areas, including scrub clearance and fire prevention measures. A well-known example is the restoration of heathland (from conifer plantation) at Farnham Heath, which began in 2002 and led to the re-introduction of sand lizards at the site in 2012.