COMMONS HABITATS:
WOODLAND
GRASSLANDS
HEALTHLANDS
WETLANDS

Habitats

WOODLAND

The Commons are a mosaic of secondary broad-leaved woodland*, acid and neutral grassland, heath and ponds on mainly thin soils over Blackheath pebble beds. The woodland component covers a far greater proportion of the Commons than the other habitat types, which is typical of the registered commons in Kent, on which over two-thirds of the ground, in total, is covered by broadleaved semi-natural woodland. Broad-leaved woodland covers only 1 per cent of Britain's land surface, but Bromley is most fortunate in having 7 per cent of its area under woodland, with Chislehurst and St Paul's Cray Commons making a sizable contribution.

  
A veteran oak on one of the Commons verges

As with many commons, secondary woodland, in this instance mainly common oak and silver birch, with an understorey of rowan and holly, has developed, as a result of the cessation of traditional management such as grazing. This secondary woodland, with holly-predominant scrub, has replaced what were large areas of grass and heathland until around the beginning of the last century. Alder buckthorn is present in damp hollows on St Paul's Cray Common. Hawthorn is frequent on woodland edges especially on Chislehurst Common, where spindle-tree and hazel also occur. Gorse ( Ulex europaeus ), which may be considered a heathland relict, is frequently found on the woodland edges. In the ground flora bramble ( Rubus spp. ), ivy ( Hedera helix ) and bracken ( Pteridium aquilinum ) are dominant, other species including cow-wheat ( Melampyrum pratense ), Solomon's seal ( Polygonatum multiflorum ), lily-of-the-valley ( Convallaria majalis ), wood anemone ( Anemone nemorosa ) and bluebell ( Hyacinthoides non-scripta ).

The secondary woodland is typical of woodland which has developed over grassland and has the following features. There are small numbers of old trees, both within the woodland and at the boundaries, in this instance supporting a few very venerable and ancient boundary pollards which are most important. The canopy is largely formed from oak and birch, the trees having grown competitively. With increasing canopy dominance the ground and shrub flora has declined in diversity with holly and bracken predominating. This tendency is being counteracted by an extensive programme of clearance of holly scrub followed by annual cutting of the re-growth.

Where the canopy has declined, either through storm damage or fire, a much more valuable scrub habitat is present with hawthorn, spindle, rowan and hazel. These areas are extremely valuable and are being maintained and encouraged, although not at the expense of grassland or heathland habitats.

The areas of secondary woodland are criss-crossed with a variety of paths and bridleways that vary in condition from hard compacted gravel to mud. These paths are well used and an integral part of the Commons as perceived by local people and a lot of effort goes into ensuring that the path margins are clear of scrub.

All too often the clearance of dense scrub, whether alongside paths or throughout a woodland area, rather than leading to the appearance of new, desirable diversity, simply enables ivy, bramble and bracken to invade new areas. This is a management challenge, but the Trustees favour opening up more woodland areas and the creation of more rides, with scalloped margins and up to 20 metres wide from the mature trees on one side to the mature trees on the other side, as this certainly opens up more pleasant vistas. Perhaps the ground flora is unlikely to be very varied on our poor soils, but even the ubiquitous ivy and bramble provide habitats for invertebrates and the woods generally support a fair range of typical insect and bird species.

The woodland ride width recommended by the Forestry Authority is 30 metres, but we consider this to be too big for such small woodland compartments as ours. The policy of opening up the footpaths and bridlepaths as rides is qualified where a route is close to a road. There we seek to maintain a screen on one side obscuring the traffic and so the shrub layer may not be cut back so deeply.

The Trustees' management commitments in respect of the woodland areas are as follows.

The surveying of boundary pollards and other veteran trees is in progress and mapping will be completed. It should be noted here that, in assessing the ages of trees, we need to examine any possible difference between the growth rates of trees in woods and in open spaces. It may be necessary to take account of the fact that our oldest trees will have started life on an open common, presumably with a faster growth rate than in later years, when they were surrounded by competing trees and a developing shrub understorey.

Areas of existing desirable scrub - meaning mixed communities of shrub-sized vegetation as distinct from the dense, holly-dominated invasive understorey present in many areas of the Commons - which cannot be returned to grassland for economical and practical reasons will be maintained through a management programme as scrub habitat and will not be allowed to develop into secondary woodland. Most areas of secondary woodland will be managed by containment and not allowed to increase in overall area.

The Trustees' Management Plan has a cautious approach to the enlargement of most of the grassy glades. The present network of footpaths, bridlepaths and glades will continue to receive priority attention. After all, they form the feature of the Commons most used by local people.

Tree-felling and scrub clearance risk adverse public comment, but we know from experience that this can be forestalled by providing information boards fully explaining the work which is being carried out and the benefits envisaged.

GRASSLANDS

The Commons support areas of both acid and neutral grassland. These must be considered, along with heathland, to be the Commons' habitats of prime importance and the Trustees' management activities seek to contribute to the overall amount of fair to good quality undisturbed grassland and heathland that remains on a county-wide scale. (On registered Kent commonlands overall only 13 per cent of the area supports unimproved acid or neutral grassland. Lowland acid grassland is listed as a priority habitat in the government's UK Biodiversity Action Plan.) The Trustees' management policy for the grasslands has been carefully considered. There are three types of treatment. Some areas, such as the May Queen site near the High Street and the green between Church Row and the Cockpit, are regularly mown during the growing season. These we consider to be recreational areas, where the grass is kept short for children's play and community events. Most roadside verges also have to be kept short. Some areas are not mown at all. This applies, for example, to the expanse of ant-hills between the Cockpit and Manor Park Road and School Road. Here the ground cover acts as a reserve for over-wintering insects and other wildlife. Yet other areas are mown once a year, after the grasses and other plants have flowered and seeded, and the mowings are cleared and removed as soon as possible. Thus the soil receives minimal nutrient addition and the nature of the flora is maintained. We are merely practicing what traditionally this would have been achieved by summer and/or autumn grazing and/or hay-cutting for winter feed.

Areas which have harebell, for example, and other wild flowers may be left in strips, uncut until the end of the season, even within the amenity grasslands. These

variations in grassland management frequently give rise to occasional enquiries from members of the public who wonder why we do not treat all of these areas as if they were lawns. We are simply trying to maintain a diverse flora and a resort for insects and spiders.

The laborious process of raking and removing the cuttings is currently undertaken by our volunteer force. Unfortunately, the hay would not be wanted by local farmers as they consider it to be too polluted by depositions from the heavy traffic on the roads which are immediately adjacent to much of our grassland.

We may be fighting a losing battle, because we are in a part of the country which is estimated to have 17-20 kg of nitrogen compound deposition per hectare per year as a consequence of atmospheric pollution. This deposition of reactive nitrogen has much the same effect as would result from leaving mowings to decay in situ : the potential to reduce plant species diversity by favouring species better adapted to high nutrient levels at the expense of less competitive plants. Researchers have found a linear negative relationship between grassland species richness and chronic nitrogen deposition, with the loss of one species for every 2.5 kg per hectare per annum increase in deposition. The most vulnerable species are Plantago lanceolata (ribwort plantain), Campanula rotundifolia (harebell), Euphrasia officinalis (eyebright), Molinia caerulea (purple moor grass), Calluna vulgaris (heather or ling) and the moss Hylocomium splendens. Euphrasia is listed as present on the Commons in Webb's history of Chislehurst (1899), but is no longer present. Hylocomium also appears to be absent.

THE HEATHLAND AREAS

Both Chislehurst and St Paul's Cray Common were previously important heathland areas and, given the priority placed on such habitats in both the UK and Kent Biodiversity Action Plans (BAP) and the Bromley BAP, the Conservators are determined to continue their work in conserving and extending the surviving and restored heathland.

Lowland heathland is considered a priority habitat because it is a rare and threatened habitat throughout the UK and Europe, with only an estimated 87 hectares in Kent, representing a decline of 95 per cent from 1,910 hectares in 1798. It is thought to be under continuing threat as a consequence of the following factors:

• loss of habitat through lack of traditional management, in particular, grazing;
• fragmentation, with unviable remnants (both genetically and in terms of management) remaining;
• acid deposition from sulphur and nitrogen oxides produced by traffic and industry, resulting in increased nutrient inputs affecting species composition in favour of grasses.
• a decline in the quantity and quality of water needed to maintain wet heath and mire systems, due to abstraction, low rainfall and climate change, and
• increasing pressure from recreational use of the land, including vandalism.

Restored heathland on St Paul's Cray Common (compartment 10, Map 1).

The heather in flower on St Paul's Cray Common

L owland heathland is characterized by dwarf shrubs such as heather (ling), bell heather and cross-leaved heath, as well as gorse and a number of grasses. It tends to be associated with nutrient-poor acid to neutral mineral soils such as sands and gravels. It should ideally contain a mosaic of heather of different ages, some scattered trees and scrub, areas of bare ground, wet heath, bog and open water. A number of birds, reptiles, invertebrates, flowering plants, bryophytes and lichens are characteristic of this habitat. Our heathland on St Paul's Cray Common and the relict patches elsewhere come into the category of dry heath, the most common type of lowland heathland, found on well drained soils in which Calluna vulgaris is typically the dominant species.

Probably the erstwhile heathland character of our local commons developed, as most such areas are thought to have done, after the Stone Age, some 3,500 years ago. In areas with poor soils, the trees were removed by cutting or burning, in order to create grazing land. The grazing, sometimes with periodic burning, then prevent tree re-growth.

Before the spread of secondary woodland and scrub, particularly from the early part of the last century, much of the Commons was lowland heathland, bearing a flora characteristic of nutrient-poor acid to neutral sands and gravels. Once grazing ceased, without positive conservation management, invasion by bracken, scrub and trees was inevitable and the heath became replaced by secondary woodland. This has been the fate of over half of England's lowland heathland over the past 60 years. There were two relict heather ( Calluna vulgaris ) areas on St Paul's Cray Common on which management and expansion began in 1993. Since then the Trustees have cleared, scraped and sown adjacent areas, most recently in 2005, amounting to 4.5 hectares in all. This heathland restoration has generally been a success and it is clear that further opportunities to encourage restoration should be taken wherever we have relict heather.

Restoration takes the form of complete clearance of an area of secondary woodland, followed by the scraping away of the peat soil until the underlying gravel is exposed. This work has been undertaken by contractors. Then, during the late autumn or winter, seed is distributed from our own areas of mature heather. It then takes around six months for the first seedlings to appear.

Our heather areas are the most cosseted feature of the Commons. Twice during each growing season they are hand-weeded by our volunteer force, removing grass, bracken, bramble, rosebay willow herb and tree seedlings and encroaching vegetation being cut back. Mature heather is cut, on a rotationally, to the base of the woody stems in the late autumn and the dry flower heads are used for seed dispersal wherever denser growth is to be encouraged. This work is done by the keepers and volunteers without the use of heavy machinery.

COMMONS HABITATS:
WOODLAND
GRASSLANDS
HEALTHLANDS
WETLANDS

THE PONDS AND WETLANDS

There are two permanent ponds on Chislehurst Common, Prickend Pond and Rush Pond, but neither is to any degree natural; both being largely, if not entirely, the result of gravel working during the 19 th century and therefore they are prone to drying up as the water table drops and in-flow ceases. The nutrient level of the ponds — which is not helped by food being thrown in for the birds — causes

de-oxygenation and algal blooms in hot weather. The disappearance of the water causes some consternation locally, but it appears that it was ever thus. The Conservators' publication, Chislehurst Commons (1977) records that the ponds dried up in the latter part of the 1950's and “The public complained and so the Conservators engaged competent water engineers who, after careful surveys, reported that they could find no reason why water should remain in the ponds at any time!” Shallow ponds, such as ours, naturally dry out from time to time with little, if any, damage to the wildlife. Indeed, some species actually require a dry period to complete their life cycle. Other Commons ponds have now vanished, including Webster's Pond, which was at the junction of Ashfield Land and Kemnal Road, and the horse pond which was at the foot of Red Hill, where the Age Concern tearoom and Sainsbury's now stand.

The northernmost pond is Prickend Pond. It is close to the High Street and its bird inhabitants ¾ typically mallard, herring gull, lesser black-back gull and Canada geese, not to mention the ubiquitous feral pigeon ¾ and the children who daily feed them are linked as cause and effect. Such is the impact of visitors that the Trustees have decided that any attempt to maintain the naturalness of the pond has to be sacrificed to its amenity appeal. The pond was dredged in 1990 and there has been little recovery of vegetation, probably due to the high bird population. In 1996 attempts at marginal planting with native species were thwarted by the scavenging geese. The pond supports minnows, sticklebacks, roach and a few carp. Being fed by run-off from the surrounding roads, its nutrient content is too high and so consideration is being given to the planting of a reed bed in the main feeder stream. This would have to be protected from the birds until it is well established. There are marginal bay willows, which have needed pollarding as recently as 2003. It has a small, artificially created island.

Nearby Rush Pond, unlike Prickend Pond, now regularly dries up in the summer months. It was dredged in 1969, when the pond was in danger of silting-up completely, and again in 1976. A major dredging and re-embankment took place in the winter of 2005. The pond has become infested with New Zealand pygmyweed ( Crassula helmsii, which is marketed as Tillaea recurva ) and native aquatics have disappeared. Marginal vegetation is limited, because, as the water level falls during the summer months, the banks become exposed and dry. Like Prickend Pond, Rush Pond is fed by run-off from the Common and surrounding roads and serious consideration must therefore be given to reducing its nutrient level by establishing a reed-bed in the feeder ditch. It also receives water from the Overflow Pond, which is at a slightly higher point on the Common. The water reaches Rush Pond via a ditch, which goes underground in order to cross Centre Common Road. The Overflow Pond now barely deserves the name as it is almost constantly dry. It receives its supply from the surface drains on Bromley Road.

Rush Pond is not so affected by visitors and so it is worthwhile to attempt to maintain some naturalness despite its vulnerability to the impact of drought. Even the ubiquitous geese and gulls tend to stay away, because there is not so ready a food supply.

The Overflow Pond and the adjacent Overflow Swamp tend to become waterlogged following sufficient rainfall in winter and the Trustees' efforts are bent towards maintaining them as wet meadows. Apart from common grasses they support an interesting wetland flora, including bur-marigold (Bidens tripatita ), common sedge (Carex nigra), lesser spearwort (Ranunculus flammula ), marsh foxtail ( Alopecurus geniculatus ) marsh pennywort ( Hydrocotyle vulgaris ), purple loosestrife ( Lythrum salicaria ) and common clubrush ( Eleocharis palustris ). There are several mature willows both in and around these wetland areas. In order to reduce transpiration loss it is necessary to weed out the seedlings and carry out pollarding of the trees.