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Woodland Habitat Audit - page 1

Definition, London’s Resource, Page 2

This audit includes all semi-natural plant communities dominated by trees or shrubs. Although there are a few intermediate habitats, the dominance of woody species generally distinguishes woodland and scrub from grasslands and marshes. London’s better woodlands have been described before, but this audit can take account of more recent information on both the woodlands and their community types, provide borough by borough statistics and identify the issues that will need to be addressed in action for London’s woodlands and scrub.

Most of London’s woodland and scrub types can be found on railway linesides and in cemeteries, if not churchyards. While the statistics for these places are included in this audit, they are covered also in the Churchyards and Cemeteries and Railway Linesides Audits because of their special land use.

Heathland is included in a separate audit; it is distinguished from gorse scrub by the presence of heather or dwarf gorse, rather than just common gorse. Hedgerows are also included in a separate audit because of their unique structural role, although the better hedgerows all fall within the hawthorn and blackthorn scrub communities.

Some of the beech and hornbeam woodlands of north London were once wood pasture, with widely spaced pollarded trees, but most have been neglected for so long that they are now woodland and are included within this audit.

The various woodland community types of London are given in Table 1. Particular combinations of plant species distinguish them. The table arranges these by the two factors that have most influence on their composition. The columns group together woodland types according to their soil reaction. On the left are chalk and other base-rich soils, and on the right the sandy, stony and peaty acidic soils. The rows group together communities according to how well drained they are, and their successional stage. In the bottom two rows are the scrub communities dominated by hawthorn, gorse or bramble which, if left alone, will change by the slow natural process of ‘succession’ into woodlands. To the top are the well-drained woodland communities with yew and beech; in the middle are the wet communities with alder and willow. In between are the moist, but not waterlogged, woodlands with oak, ash, hornbeam, sycamore and field maple.

Although the table includes a large number of woodland and scrub communities that may occur in London, the next section of this audit shows most of them to be uncommon or rare.

The best statistics for London’s woodland and scrub cover come from the London Wildlife Habitat Survey of 1984/85, held by the London Ecology Unit. While these statistics are known to be slight underestimates, and there will have been minor changes over the years since the survey, the errors should not be large as they result mainly from the exclusion of a number of very small blocks of woodland and scrub. The most significant exclusions were of the smaller areas on London’s railsides and hedgerows distant from other valuable habitat. The majority of the area is found in large blocks that were all documented in the survey and almost all of which have not changed since the survey.

The following table illustrates the range of woodland and scrub plant community types found in London and the table in the Appendix London's Wood and Scrub Communities considers each in detail. The amount of woodland and scrub in London is shown in a separate table.

The 7,300 ha (4.5% of Greater London’s land area) of woodland documented in the Wildlife Habitat Survey is known to be a good estimate of the total. Woodland is the second most extensive natural habitat of London (after unimproved and semi-improved neutral grassland). Much of the woodland (5,900 ha or 3.7% of London) is native broadleaved woodland. There are some 1200 ha of non-native broadleaved woodland (predominantly sycamore, 0.8% of London) and small amounts of coniferous woodland (160 ha not native to the London area, 0.1% of London) and fen carr (16 ha, 0.01% of London). The area of scrub in London is some 1,600 ha (1% of London). This last figure is likely to be a less accurate estimate than the woodland figures, given the smaller size of most patches of scrub.

Figures 1, 2 and 3 give the distribution of native woodland, non-native broadleaved woodland and scrub from the Habitat Survey (not yet available on line). These Figures are also presented as simpler maps, with the total amount of habitat in each borough represented by a dot of proportional size. There is a good correlation between the amounts of all four habitat types across London Boroughs, showing that a borough with much native broadleaved woodland tends also to have more non-native and coniferous woodland and much scrub.

Figure 1 shows that native woodlands are numerous and scattered over Greater London, so that few areas are further than two kilometres from a woodland. Good concentrations of woodland occur in the north of Hillingdon, at Hampstead Heath, Wimbledon Common and Richmond Park, Epping Forest, the north of Redbridge, Oxleas, Dulwich (remnants of the ‘Great North Wood’) and especially in the south of Croydon and throughout Bromley. Most of these concentrations are on high ground. There is a dearth of woodland in central London and on the low-lying land east of there and north of the Thames, and a similar void west of the Lea Valley. These areas are predominantly low ground and were easily worked for agriculture.

Figure 2 shows that the distribution of non-native broadleaved woodland, although still predominantly on higher less easily worked ground, is not so concentrated, so helping to fill the gaps in the distribution of the native woodland. Almost all the areas are small (less than 20 ha), with the notable exception of the sweet chestnut woodland of Lesnes Abbey Wood in northern Bexley.

Figure 3 shows that the very many small areas of scrub are even more widely scattered. Although they occur with the woodland, there are also concentrations in the river valleys of the lower Thames, Lea, Brent and Colne and a notable concentration at Mitcham Common.

The London Ecology Unit holds the parcel-by-parcel details of all the woody habitat summarised in Table 1 above (and for many boroughs a more detailed re-survey). The most recent data should be the starting point for an individual borough audit.

When the Habitat Survey was undertaken the best classification of woodland types was that of Peterken, which largely employs the woody species. Since then the National Vegetation Classification, which is the basis for the communities in Table 1 and takes all plants into account, has been published, but much of the survey material for London pre-dates this time and presents difficulties in determining the NVC community types.

For this audit, the information on London’s best woodlands, those included within a Site of Metropolitan Importance for nature conservation, was reviewed and the best approximation to the NVC types determined. The woodland in these sites totals 3,200 ha, nearly half of London’s woodland, and so is a good sample, if biased towards the older and larger woods. This analysis is not yet complete, so that the following paragraphs will be subject to revision. Figure 4 shows the amount of each type in the Metropolitan Sites and a table of Sites of Metropolitan Importance gives the data on which this is based.

Three woodland types comprise the majority of London’s woodlands. The largest single category is the woods of moist neutral soils, the oak-honeysuckle-hornbeam-sweet chestnut woods. This type is found in most of the woodland Sites of Metropolitan Importance, except for some of those on chalk, Southeast of London. Within this category is the sweet chestnut woodland of Lesnes Abbey Wood and most of the hornbeam woodlands of Ruislip, Epping Forest and Hainault Forest. The hornbeam woodlands are distinctive of London and the nearby area of the Southeast.

The second largest category is the ash-maple-sycamore woodlands, and these are even more widespread in the Metropolitan Sites than the oak-honeysuckle woods. The older stands of these woodlands on the chalk in Croydon and Bromley can have a rich flora, but many of the recent secondary sycamore woodlands are botanically poor.

The third category is the oak-birch woodlands of acid soils. These tend to be on the old heaths and commons, such as Wimbledon Common, Epping Forest and Hampstead Heath and in other places on sandy and gravelly soil, such as on top of Croham Hurst, at Petts Wood, Ruislip woodlands and Lesnes Abbey Woods.

Hawthorn scrub is the next largest type, found in a wide range of sites, but especially in the Farthing Downs site in Croydon and in Epping Forest. The Metropolitan sites probably underestimate the amount of this habitat in comparison with the woodlands.

The beech woodlands come next in order of abundance. Many of these were difficult to classify by type, but there are certainly beech hangers on the chalk in Croydon and Bromley, which is where most of these three types are found. The beech woods of north London are beech-bramble and acid beech types.

There is very little yew woodland in London, Cudham Frith in Bromley having a small area on a steep chalk scarp and there just may be a small area also in the West Kent Golf Course Woods.

Wet woodlands in London are many, but small and scattered. The largest areas are found in the mid-Colne Valley and Ingrebourne Valley. The most widespread type is probably nettle woodland, but there is not much of this species-poor type in the Metropolitan Sites. Another species poor type, grey willow carr, occurs in and around old gravel workings in both valleys. There is a small area of swamp carr at Bewick Ponds on the Ingrebourne and small areas of Alder flush woodland where springs and flushes occur elsewhere in London’s woodlands, as at Petts Wood. Birch-purple moor-grass woodland occurs on the plateau of Wimbledon Common.

Gorse scrub occurs on the old commons, such as Mitcham Common, Wimbledon Common and on other acid soils, such as at Epping and Hainault Forests and the Ruislip Woods.

Figure 4: The amount of different woodland types in London’s Sites of Metropolitan Importance (incomplete analysis July 99). To be added.

Woodland Audit Contents, Page 2, Amount of Woodland and scrub, Sites of Metropolitan Importance, London’s Woodland and Scrub Communities

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