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Woodland Habitat Audit - page 2

  Nature Conservation Importance, Threats and Opportunities, Page 1

Nature Conservation Importance

There is no doubt that London was very largely clothed in woodland before the activities of man induced the other ancient habitats. Even nowadays, after millennia of management, the composition of the ground flora of the older woodlands is derived from this wildwood. But there have been many losses, and the composition of woodland canopies more reflects their long history of management, so that species like hornbeam, sweet chestnut, field maple and hazel are more abundant than they would be naturally.

The value of ancient woodland for nature conservation has long been recognised. The correlation between ancient status and nature conservation value in London is good. Most of the larger ancient woodlands in London are included in Sites of Metropolitan Importance and there are not many parts of the Metropolitan Sites that are not ancient. However, the correlation is not absolute, so it would be dangerous to assume that all valuable woodlands are ancient or that all ancient woodlands are valuable. This audit considers survey data from woodlands in London and so enables a better evaluation than the simple two-way classification into ancient or not.

For plant community conservation, hornbeam woodlands must be important given that London is in the centre of their restricted national distribution. The larger areas of these woodlands also support some uncommon species in London, such as the hawfinch, marsh tit and spotted flycatcher.

National priorities that should be considered in London are for wet woodlands and beech yew woodlands. The national action plan considers wet woodlands important for the conservation of bryophytes, invertebrates and the otter, in London their rarity should give them importance.

The national plan or beech and yew woodlands lists several rare species, some of which are found in the London examples. Coral-root bittercress occurs in Old Park Wood on the chalk in northwest Hillingdon and bird's nest orchid is found in the deep shade of some of the beech hangers in Bromley, and there are records of violet helleborine from the beech woods across London's northern fringes. The national plan also identifies two priority fungi and a moss.

There is a valuable mosaic of chalk scrub, woodland and grassland on some sites in the south of London (such as Farthing Down), which not only holds many uncommon plant species, but provides a wide range of resources for uncommon animals.

The scrub and woodlands of moist soils are not included in national priorities, but they must be considered important in London, as they provide the majority of our valued woody cover. Woodlands like Oxleas, the National Nature Reserve Ruislip Woods, Lesnes Abbey Wood, Dulwich and Sydenham Hill Woods, Petts Wood and 60 Acre Wood are all on these soils. These soils, too, support almost all of the secondary woodland that plays a vital strategic role in areas otherwise deficient in woodland. These places help to sustain a wide variety of animal species that provide the everyday biodiversity for Londoners to enjoy, including birds like the nuthatch, woodpeckers, leaf warblers, tree creeper and bullfinch.

The scrub of London's railsides, commons and wasteland also plays a valuable ole, providing nectar for butterflies and sustaining birds like the wren and dunnock, as well as less widespread species like whitethroats and linnets.

Most of the birds appreciated in the back gardens of suburban London are those of woodland and woodland edge: the tits, robin chaffinch dunnock, wren, greenfinch, song thrush and even the blackbird. Garden invertebrates with similar ecology include the holly blue and speckled wood butterflies. Even the stumps of dead trees support the stag beetle. It is the woody vegetation of gardens that helps to support the stag beetle. It is the woody vegetation of gardens that helps to sustain London's populations of such species, so there is a strong link between London's scrub and woodlands and the everyday biodiversity conserved in gardens.

Threats and Opportunities

Threats

Many wet woodlands have a dense structure, often with fallen trees, difficult ground conditions and mosquitoes. This makes them more difficult to enjoy and so less appreciated by the public than 'bluebell woods'. They are threatened with changes in the water regime through drainage or flood control work, succession to drier habitat and toxic water pollutants/ The tradition of pond maintenance to arrest succession to wet woodland prevents the development of many small wet woodlands.

Opportunities
There has been a national drive for woodland planting, manifest in and around London in the Watling and Thames Chase projects. The aims of these projects extend far beyond biodiversity conservation, but they provide an excellent basis for the development of new woodlands for people to enjoy. The framework of Table 1 and Appendix 2 should provide a good basis for what is sensible to create according to soil conditions. There are also less obvious opportunities, such as allowing wetlands to develop into wet woodland through natural succession, which would be appropriate in disused mineral workings. Tree planting can, however, cause harm to nature conservaton, as trees shade out other valuable plant communities in grassland, heath, wasteland or marsh. It is vital therefore that new woodland planting is undertaken only after survey of the existing plant communitiy confirms that it is of no species value for nature conservation.

The greates need for new woodlands and scrub is in the heavily developed low land and inner boroughs of London, but it is there that space is at a premium. In such areas the natural succession to woodland that occurs on abandoned land or in the old cemeteries is a gift of woody vegetation that must be accepted. Such places provide some of the only woodlands in wide areas of London and a significantly better habitat that is available in ordinary planting.

Where there is space in a wetland, allowing succession to wet woodland will provide a valuable habitat. Rather than reverse the succession in a pond, if there is room, it is preferable to create a new pond and allow the old one to become wet woodland.

Woodland Audit Contents, Page 1, Amount of Woodland and scrub, Sites of Metropolitan Importance, London’s Woodland and Scrub Communities

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