The Flora of Big Wood

Introduction

Big Wood is a fragment of ancient woodland (i.e. in existence since at least 1600 AD) lying in the southern part of the London borough of Barnet (centred on grid reference TQ 256887). The Wood covers an area of 6.88 hectares (16.98 acres), with Little Wood adding a further 1.72 hectares (4.25 acres). The two Woods are clearly shown on Rocque’s map of 1754. A brief account of the Woods and their history is given by Hewlett et al (1997) and further useful information (and a map) are contained in a leaflet published by London borough of Barnet, c.2013. The Wood lies on the London Clay and was regularly coppiced until the early nineteenth century. The Wood was clear-felled around 1810 and there is no evidence of rgular coppicing after that date. In recent years there has been a welcome revival of small-scale hazel coppicing (or glade creation).

The Botanical Survey

A botanical survey of the flowering plants and ferns of Big Wood was carried out during the summer of 2015. Three visits were made to the Wood – on May 1st, July 12th and August 11th. The visits lasted three hours on each occasion, giving a total of nine hours recording. Care was taken to visit all parts of the Wood on each visit. As expected, the woodland edges and path-sides proved to be more diverse than elsewhere, so more time was spent surveying these areas. Particular care was taken to look at the six recently cut glade areas shown on the map in the London borough of Barnet’s leaflet (c. 2013). Voucher specimens of a number of critical plants were taken and have been deposited in the author’s herbarium. References are made to a plant list compiled by the London Ecology Unit (LEU) in the mid 1990s. This earlier list included plants from the adjacent Little Wood, which was not included in the current survey.

Results

A total of 112 taxa (species, subspecies, and named varieties) was recorded. Table 1 lists these taxa by both English and Latin names and by order of frequency. The status of each taxon is shown. Native plants (N) are those that are native in Middlesex; Introduced natives (I) are those that are native elsewhere in England, but introduced in Middlesex; Archaeophytes (Arc) are ancient alien plants known to have been introduced before 1500 AD; and Neophytes (Neo) are more recent aliens, introduced after 1500 AD.

There were 73 Natives; 6 were Introduced natives; 32 were Neophytes, and there was a single Archaeophyte. A further 23 species were recorded earlier by LEU (Table 2), but some of these may have only occurred in Little Wood. They are listed here as some may be refound in Big Wood. Two further plants were recorded by Hewlett et al (1997), but were not on the LEU list or seen during the current survey. These are Sessile Oak and Wood Melick. They are both ancient woodland indicators (see below) and may have been overlooked.

Discussion

Native plants

71% of the flora of Big Wood was native. These are the plants that give the Wood its “natural” character. They also provide the Wood with its greatest ecological resource – food and shelter for other organisms. Ancient woods are highly valued for the diversity of wildlife that they support, and most of that diversity derives from the native flora. The Pedunculate Oak, for example, a frequent canopy tree in Big Wood, supports (together with its close relation the Sessile Oak), 423 associated insect species in the UK (Kennedy and Southwood, 1984). Two kinds of Hawthorn grow in the Wood – the Common Hawthorn (around the edges) and the Midland Hawthorn (more centrally), but the most widespread is the hybrid between the two. 209 species of insect have been recorded in association with these hawthorns (ibid.) and their berries are an important source of food for a range of birds including the Mistle Thrush, a declining species that is known to breed in the Wood (Darrell-Lambert, 2015). The 70 other listed native species all make their own contribution in this way to the overall biodiversity of the Wood. It is instructive to compare the native flora of Big Wood with that of neighbouring Queen’s Wood in the borough of Haringey, where a similar survey was recently carried out (Bevan, 2010). Queen’s Wood is about three times the size (21 hectares), but in other respects, including the underlying geology of London Clay, the two Woods are very similar. Both are surrounded by houses with gardens. A total of 225 taxa was recorded from Queen’s Wood, of which 136 (60%) were native. The larger overall number of taxa present reflects its greater size, but Big Wood supports a significantly larger proportion of native plants – 71%. This is likely to be a consequence of the longer edge habitat in Queen’s Wood, which allows a greater proportion of alien plants to penetrate into the Wood from adjacent gardens.

Ancient Woodland Indicators

Certain native plants are closely associated with ancient woodland. Francis Rose (1999) listed 100 such species, which he believed to be characteristic of ancient woodland in South East England. Such plants, occurring in Big Wood, are shown in Table 1 with the acronym AWI (Ancient Woodland Indicator). 23 species were found during the current survey, with one further species (Lily-of-the-valley) recorded by LEU (Table 2) and two (Sessile Oak and Wood Melick) are mentioned in the GLA Barnet Handbook (Hewlett et al., 1997). This total of 26 AWI compares well with the three-times larger Queen’s Wood, which supports 41.

Wild Service

One of the best examples of such plants is the Wild Service-tree, a “rare and decreasing tree” in Middlesex according to Kent (1975). It is remarkably widespread in Big Wood. Hewlett et al. (1997) describe how, in a recent survey by local residents and representatives from the Forestry Authority, they noted 104 specimens (including young trees growing up as suckers from mature trees). The current survey confirmed their frequency in the Wood today and they remain a remarkable feature.


C

Crab Apple

Equally striking is the large population of another AWI – the wild Crab Apple. Rackham (2003) describes these trees as “anti-gregarious”, but in Big Wood there is an unusually large population, the oldest of which are thought to be around 140 years old (Hewlett et al, 1997). True Crab Apples are rare and declining in the London area and usually occur only sporadically as Rackham states. None have been found in Queen’s Wood for example, and only two in neighbouring Coldfall Wood, so the large Big Wood population is noteworthy.

By contrast, another AWI plant, Tutsan, is very rare in the Wood and I was only able to find a single individual (at TQ 255 888, close to the northern edge of the Wood where it abuts onto the gardens of Denman Drive South). It is possible that this plant could have regenerated from buried seed (certain species of St John’s-wort can survive for over a hundred years in this fashion), but it seems more likely that it was bird-sown from a local garden as Tutsan is sometimes grown as an attractive ornamental shrub. Whatever its origins, it is a striking addition to the flora.

Tutsan

Alien Plants

The 33 alien species make up 29% of the total flora and reflect the urban nature of the Wood and its surroundings. As mentioned above, these non-native plants have recently been sub-divided into two categories according to their supposed dates of arrival (Stace & Crawley, 2015). By far the largest sub-group in Big Wood are the neophytes – plants thought to have established in Britain after 1500 AD. These are largely those that have “escaped” from local gardens. The much smaller sub-group, the archaeophytes, arrived before 1500 AD. Only one such plant was recorded from Big Wood in the current survey – the Wild Plum, whose ancestors appear to have derived from hybrids between the Blackthorn and the Cherry Plum. Ground Elder (introduced as a “pot herb” by the Romans) was listed by the London Ecology Unit in their earlier survey. This can be very invasive and is often a serious bane to gardeners and. It should be removed if found.

The relative abundance of neophytes around the edge of the Wood is a common feature of London’s woods. In the recent survey of Queen’s Wood, for example 40 % of the flora was found to be alien (Bevan, 2010) and most of these were neophytes. Among the more unusual neophytes in Big Wood was Bohemian Knotweed, the cross between the notorious Japanese Knotweed and its close relative the Giant Knotweed. The identity and origin of this rare hybrid has only recently been worked out (Bailey et al, 1996). It can be just as invasive as its parents but appears to be intolerant of dense shade. It does not seem to be causing any current problems in the Wood, but it needs to be kept under observation. It could become a nuisance, for example, if it spread into one of the recently created glades. Another Knotweed relative, the Russian Vine, occurs at the edge of the Wood, where it has spread in from an adjacent garden but, as a light-demanding climber, is unlikely to penetrate very far into the interior of the Wood.

Concerns are sometimes expressed about the potential effects of the hybrid bluebells, which are widely distributed in the Wood, particularly around the edges. The hybrid is a cross between the Spanish Bluebell, sometimes grown in gardens, and our native species. The two taxa are interfertile and “hybrid swarms” can result. In time, it is feared, such introgression could affect the genetic integrity of the native species. Most London woods are affected to a greater or lesser degree. In Big Wood, good populations of apparently pure native bluebells appear to be thriving and there are large numbers of the white albino form. The large size of some of these populations may have protected them from any major introgression.

Bluebells

A few vigorous aliens will need to be controlled, particularly where they encroach onto the glades. The Bohemian Knotweed has already been mentioned in this regard, but Yellow-flowered Strawberry is currently more of a problem and spreading fast in the southern glade near the Temple Fortune Hill entrance. The variegated Garden Yellow-archangel, which is also spreading close by in the southern corner of the Wood, will also needs to be watched, though I hesitate to recommend removing it as it is such a beautiful plant. Care should be taken to make sure that it doesn’t spread from its “hidden corner”.

The Three-cornered Garlic can also become very invasive (Stace & Crawley, 2015). It is particularly troublesome in the West Country, but now seems to be spreading in parts of London. It needs to be “kept under observation” and controlled if necessary.

Recent glade creation.

The Big Wood Volunteers created six small glades (as shown on the map in the London borough of Barnet’s leaflet) during 2011 and 2012 with a view to increasing the ground flora of the Wood and to encourage oak regeneration. Several of the over-abundant hazels were coppiced in these areas during the winter months The results have been encouraging, allowing a range of light-demanding species to appear. The largest of these glades, in the north-east corner of the Wood, has been particularly successful, with many foxglove seedlings appearing at the time of the survey. In addition, there were many recent seedlings of the Three-nerved Sandwort, an AWI species not seen elsewhere in the Wood and not listed in the earlier LEU survey. This species is thought to survive for many years in the seed bank (Grime et al. 2007). Successful oak regeneration however may be more of a problem. Rackham (2003) has shown that oak now seldom regenerates within woodland owing to a combination of factors including the presence of the oak mildew fungus (Microsphaera alphitoides) and the shady conditions of most woods today. The glades will certainly help in reducing shade, but it is doubtful that this will be sufficient to allow natural oak regeneration. My experience in creating large coppices in two local woods (Queen’s Wood and Coldfall Wood) is not encouraging (Bevan, 2011). In neither Wood has there been any evidence of successful oak regeneration within the coppices. Plenty of oaklings appeared in the couple of years following the coppice cut, but these all succumb to the oak mildew by the third year. The only way to allow the oaklings to avoid this fate would be to grow them on in suitably sized containers in well lit conditions outside the Wood, and to plant them back into the glades when they are four or five years old and able to resist the fungus. This could be a valuable, if challenging, task for the volunteers to undertake. Alternatively, acorns could be collected and the resulting oaklings grown on for eventual reintroduction to the coppices. I would be happy to give further advice on these procedures.

These glades have become a most valuable feature of the Wood, currently supporting 29% of the Wood’s entire flora. They should be maintained and enlarged wherever possible. It will be necessary to cut back the hazel on an annual basis and to control bramble invasion wherever required. Overhanging canopy branches should also be removed; the aim being to let in as much light as possible. Botanical monitoring should be continued, as further regeneration from buried seed is likely in the future. Buried seed of some woodland species, such as Foxglove and Slender St John’s-wort, can persist for more than a century (Buckley, 1992). However, as it is now more than 200 years since the Wood was last regularly coppiced, it is unlikely that many ancient woodland seed bank species will have suevived.

Comparisons with the earlier London Ecology Unit plant list.

The survey carried out in the mid 1990s by the London Ecology Unit listed 84 species from Big Wood and Little Wood combined, and is likely to have been compiled after a single visit (Michael Waite, pers. com.). That survey is not therefore strictly comparable with the current one, which covered Big Wood alone. Moreover, the visit is unlikely to have taken place before July as neither Wood Anemone or Lesser Celandine were listed. These are both striking spring-flowering plants, unlikely to be missed, that disappear from view by July, and were both found to be locally common in the current survey. Nevertheless, some observations about the two surveys can be made. Most of the 18 species found on the LEU survey that were not seen currently (Table 2), are common and widespread, and some may have been overlooked in the current survey .Two species in particular should be looked for in future: – Lily-of-the-valley and Bracken. The first of these is an AWI, but can also sometimes escape from gardens. Bracken was refound in 2017. The delicate Wood Meadow-grass has also become scarce in London woods, and it would be good to re-find it. It is a charming grass, which is easily overlooked. Native Hedge Bindweed, also seen in the earlier LEU survey but not currently, is a very common plant in the countryside, but in London it has become rather scarce in recent years as the closely related, but alien, Large Bindweed, has taken its place. The latter was the only Bindweed seen in Big Wood currently, and the two surveys may have witnessed the demise of the native species. Finally, Common Comfrey, which is far from common away from water in London, was listed in the LEU survey but not seen in 2015. The widespread species away from water is the Russian Comfrey (S. x uplandicum), but this one was not found either. It would be interesting to re-find either of these taxa.

Conclusion

Big Wood is a valuable fragment of ancient woodland, which supports a rich and diverse flora as set out in this report. Many of the native species found are characteristic of such historic woodlands and will have been present here for many hundreds of years. The suggested management proposals, and in particular the maintenance of the glades, should ensure that the Wood continues to thrive into the future.

Acknowledgements

I am grateful to Susan Osborn and Peter Falk for commissioning this botanical survey, and for much helpful information about Big Wood. Mike Waite provided useful comments on the LEU Survey. I am grateful to Dr David Corcoran for technical assistance in setting up the tables and preparing the photographs.

References

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