The Great Oaks

Defying expectations, One Tree Hill has many trees and is in a state of mixed oak, sycamore and ash woodland with a number of significant remnant boundary trees of oak, ornamental plane tree and poplar plantings. The secondary woodland of ash, oak and sycamore is ‘infill’, with standard trees, some of which have been present on the Hill for centuries, becoming swamped by new growth. There are more oaks to be found along the boundary with the One Tree Hill allotments at the entrance from Honor Oak Park. One of the oldest oaks is probably veteran and could be of ancient status, unlike the Oak of Honor which was planted in 1905 after the previous oak, reputedly planted by Queen Elizabeth 1 in 1602, was struck by lightning.

The first signs of managed woods in Britain were in the Anglo-Saxon times and One Tree Hill was managed for its stock of trees many centuries ago. The Great North Wood is and was a combination of oak and hornbeam with a hazel under storey. These are trees that were vital for the development of London and for the sustenance of local communities. The sessile oak trees that colonised of their own accord grow straight and tall, making excellent timber for housing and ship building.

Timber was too vital a resource to be cleared away. Oak was strong and its acorns provided a good food source for pigs, a grazing practice known as pannage. Hornbeam, another strong wood, made excellent, slow burning firewood, and is thought to have gradually established its dominance in London’s woods from the tenth century BC (Fritter 1990 p.24). When early peoples hacked their way through hazel they found that it did not disappear unless uprooted and when it grew back it provided beautifully glossy, straight, flexible poles. It also produced delicious nuts, something that would have been well known to Neolithic farmers. The hacking back of trees allowing them to regrow to be harvested again for their produce, is known as coppicing. Cutting a tree to its base was a well-managed, organised industry in the Great North Wood, including Honor Oak. The once rural nearby area that we now know as Norwood had eight coppices. They were fenced ‘to protect them from the depredations of men and beasts, and patrolled’ by servants (Fritter, 1990 p.24). The Great North Wood was renowned for its coppices not only of hazel but also of oak, whereas in nearby Kent, small-leaved lime coppices, cut by the Romans are still alive and sprouting to this day.

One Tree Hill was once managed oak woodland belonging to the monasteries that owned swathes of land in south London. This all changed with the dissolution of the monasteries by Henry VIII followed by a series of acts of parliament between the 1720s and early 1800s legalising the enclosure of common land. Politicians used the Napoleonic War food shortages as a reason to encourage enclosure of the commons. The 500 acres of Sydenham or Westwood Common which covered modern day Forest Hill were enclosed in 1810, Dulwich Common was enclosed in 1805, and 3,000 acre Penge Common was enclosed in 1827. It was the beginning of the end for the commoners and for local people whose livelihood had depended on free access to lop and harvest from the Great North Wood.

Native and non-native species

Whilst the oak woodland remained, the ecology was probably similar to Dulwich Woods today with wildflowers consisting of wood anemone, English bluebell, dog violet, wild garlic, woodruff and possibly columbine, wild strawberry, wild daffodil, Solomon’s seal and rarer species like herb paris and helleborines - orchids that can still be found in remnant ancient woods of Croydon and even in nearby Lewisham. Once these separate woods and their species were connected by woodland cover, the sustained oak woods would have been rich in fungi, with species like oak bracket and beefsteak fungus commonly occurring; the latter is still present on One Tree Hill. Wood, including underwood and brash, was a valued asset to people in centuries past so very little would have been wasted. It was used for heating and cooking as well as making tools, utensils and furniture. Contemporary One Tree Hill with its standing deadwood and log piles may be more hospitable to deadwood invertebrates (known scientifically as saproxylic invertebrates) than during times of human dependence on local woodland resources. In 1990, local entomologist Richard Jones conducted a preliminary invertebrate survey that found four species of invertebrates which may have survived from the days of ancient woodland. One slightly more accessible indicator of ancient woodland lineage is the purple hairstreak butterfly, an insect that can only really be seen in the canopy level of oak trees, unless spotted when it comes down to feed on bramble honeydew in the summer. The first ecological record at One Tree Hill is of the purple hairstreak, published in 1766 in The Aurelian by Moses Harris. This overlooked butterfly was ‘commonly taken in plenty in Oak-of-Honour Wood, near Peckham, Surry’ (Frith and Lloyd 1995 p.3). There have been few sightings since, though this could be because it is a difficult butterfly to see. There are a number of other species that can be observed, however: red admiral, peacock, small white, large white, green-veined white, orange tip, holly blue, gate keeper, meadow brown, comma, speckled wood and small and large skippers have all been recorded in recent years. Moth data is poor for One Tree Hill but there are some historical records. The blotched emerald Comibaena bajularia was first named the Maid of Honour when it was recorded in 1836 at One Tree Hill by lepidopterists and named after the famous oak. Since its food plant is the oak and it prefers established woodland with mature oaks, it was well suited to the old Oak of Honour Wood.

When the oak woods of One Tree Hill were cleared in the early 19th century the landscape became favourable for grazing of livestock and for the growth of sun-loving plants and invertebrates. The change would have encouraged the spread of gorse, a prickly bush in the pea family which was often known as ‘furze’. On the old Sydenham Common (now the town centres of Forest Hill and Sydenham) the gorse was cut to encourage re-growth for the grazing of commoners’ livestock. There are still residual fungi growing on the Hill that are more representative of grassland than woodland.

One Tree Hill today shows evidence of mankind’s global influence over the natural world. There are a number of non-native species, some of which are invasive. The London planes which can be found across the hill on either side were planted in the early 20th century, as they were in many green spaces across London. Hyde Park, Green Park, Highbury Fields, Southwark Park and Peckham Rye Common all have a large number of planes. This is not an ideal situation for wildlife, or for people. In France, miles and miles of plane trees are being felled because of fungal infection. Since the end of the last glacial period nature has thrived on diversity, evolving to form dependency bonds between species, relationships termed ‘symbiotic’. The pollination of trees and wildflowers by insects, or the mycorrhizal relations of tree roots and fungi are good examples of this as is reliance on a range of bumblebees, solitary bees, wasps, flies, beetles, butterflies and moths that pollinates the crops on which society depends.

Nature’s response to the plane trees on One Tree Hill has been to kill them through competition for light, water and nutrients. The plane, a hybrid of American and oriental trees, is unable to reproduce nearly as vigorously as native oak or non-native sycamore. The plane tree’s leaf is so dense and takes such a long time to break down that on the Brenchley Gardens side of the Hill there is little soil-based fungi fruiting in autumn and winter because the plane leaves act as long-term mulch in a place that requires regeneration rather than repression. Oak and sycamore saplings can be seen growing up against the trunks of the planes, some already dead and standing to provide habitat for the important invertebrate recyclers woodland requires (Jones 1990). There is no doubt the planes are splendid trees but for too long the philosophy of councils and land managers in London has been to plant plane and plane only. The recent outbreaks of Massaria, a fungus that is found naturally on planes to control the number of branches and aid irrigation, has increased greatly in parks and green spaces in north London where many planes have been planted. In truth, One Tree Hill may need no planting at all, other than the occasional re-creation of lost hedgerows, although along the Honor Oak Park fence wych elm, ash and hawthorn have seeded themselves without human help. Arguably it is impossible to recreate the richness of natural woodland through tree planting.

Another undesirable non-native species is cherry laurel. Originating in the Balkans, cherry laurel is an evergreen shrub that can quickly establish as a sprawling tree, with large, dense limbs. For humans its leaves and seeds are poisonous because they contain cyanide. Ecologically, laurel shades out and outcompetes anything underneath so the biodiversity of a wood is reduced and its habitats degraded. In recent years the Friends have been acting to reduce the amount of laurel on the Hill and already the results are evident. The great benefit of the management of One Tree Hill’s old woods was that light would have come in when trees were felled, nourishing the wildflowers in the herb layer and providing a base layer for the wider woodland ecosystem. Another argument is that these processes of light and shade interchange naturally over longer periods of time (tree time is centuries, human time is decades). But the need for our green spaces to be managed is strong. Such is the pressure on green space that any place that is not used by people or properly designated risks being seen as dead space and vulnerable to development and to ecological degradation.

There are a few false acacia trees on the slopes close to St. Augustine’s Church, another invasive species which originates from overseas. Originally endorsed by William Cobbett for its value as firewood, false acacia is a highly invasive species in central and eastern Europe, where species-rich woods and grasslands have been overcome by this fast growing and dominant tree. Like the London plane, false acacia can be found planted as an ornamental tree for its spring blossoms in parks, Victorian gardens and even along London’s South Bank.

One non-native, naturalised species that causes less harm to British wildlife is the sycamore. Pilloried for decades because it is fast growing and its waxy leaf is the official ‘leaf on the line’, the sycamore has been enthusiastically ripped out of nature reserves across London by volunteers. At our winter tree walk in January 2014, we watched one attendee drop to his haunches, groaning as he attempted to pull a sapling from the ground. If sycamore is invasive, young trees growing now will never reach the canopy due to the damage caused by the, also invasive, grey squirrel. Ironically Jones argues that these damaged sycamores are excellent habitats for deadwood invertebrates.

One Tree Hill’s ever changing Wildlife

There has been recent evidence to show how important the sycamore is for nesting birds in the spring time, of which One Tree Hill supports many species: wren, robin, nuthatch, great tit, blue tit, long tailed tit, dunnock, chiffchaff and blackcap. The majority of birds are resident species found all year round but some travel long distances to visit the hill. Chiffchaff and blackcap are migrants, some of which will travel from Africa and southern Europe to nest at One Tree Hill, though some blackcaps visiting in the winter are likely to be central European birds fleeing cold snaps. Both species are thought to be overwintering in Britain due to milder winters. The garden warbler has been recorded on several occasions, often in May around the time of the annual Dawn Chorus walk. In April 2013 a garden warbler was feeding on blackthorn flowers atop the hill. Swifts, seen each year scything over the hilltop, are often mistaken for bats during public walks. But some migrants have been lost. The spotted flycatcher is a bird that suffered an 89% decline between 1967 and 2010. It was recorded as a breeding bird in the 1990s at One Tree Hill but this decline is not London specific; it is reflected nationally for many different reasons. The bullfinch, the male of which has a striking pink breast, is another species lost from One Tree Hill since the 1990s and from the local area, though there have been recent records along the River Pool in Lewisham and it still breeds in parts of Croydon. One reason why One Tree Hill is less suitable for certain birds than it was decades ago is that it has changed in structure from mostly scrub overtaking open land. For example, One Tree Hill could not have supported great spotted or green woodpeckers in 1905 whereas by 2015 its maturing woodland habitats and standard trees provided shelter and nesting space. The work of cavity creating woodpeckers also benefits bats, though currently the young woodland and lack of suitable mature trees across the woodland habitats of One Tree Hill means the variety of bat species is limited. Bat walks since 2011 have only recorded the soprano and common pipistrelles but a bat survey in 2015 on neighbouring Camberwell New Cemetery recorded leisler and noctule.

As a reserve which supports so many bird species, there is a plain attraction for birds of prey. Tawny owls breed in the nearby Sydenham Hill and Dulwich Woods complex, as well as at Nunhead Cemetery. Residents near One Tree Hill often hear them calling at night. Whether they are breeding or merely using One Tree Hill to hunt remains unknown, but the fact that their territories are a mere kilometre in size does give the sense that they are nesting nearby. Kestrels can be seen visiting St. Augustine’s Church, looking for a meal of wood mouse or other small mammals unknown to us. The kestrel’s cousin, the hobby, has been seen migrating over Forest Hill Road and bred in the Sydenham Hill and Dulwich Woods in 2015, so it is sure to pass through unseen. London’s peregrine falcon pairs numbered 27 in 2014 and they have been known to breed near Crystal Palace and to hunt around the Southwark and Lewisham border. Sparrowhawks are a common visitor, recently seen hunting ring-necked parakeets over the main glade of One Tree Hill. The splash of feathers often found on the grass and on the path is a sign of a sparrowhawk having surprised and devoured a grounded woodpigeon. The buzzard is now Britain’s most common raptor and is becoming a common visitor to the Dulwich Woods. There is also the outside chance that little owl, breeding in parks and playing fields around Dulwich Village, could find One Tree Hill suits its needs in decades to come if the mosaic of open grassland and mature oaks is maintained.

The Future of One Tree Hill’s Wildlife

As a Local Nature Reserve adored by many for its sudden shock of wildness and stunning, leaf-edged views of Central London, One Tree Hill is safe. Its topography is unsuitable for development and Southwark Council have never proposed this. Though clearing trees from old grasslands can be a worthwhile conservation project depending on the location and habitats, it would be pointless at One Tree Hill where oak is establishing new woodland. The open land would be of no greater value than the naturally occurring woodland ecosystem currently maturing on the hill. There have been wry suggestions of clear felling of trees to open up views or ‘see what a nice piece of land it is’. This is something that should be rejected on the grounds that the woods provide much greater benefit to people and wildlife. But there are still issues beyond the hands of authorities like the Friends or the Council which could threaten One Tree Hill’s wildlife and ecology. The spread of invasive species such as ash dieback disease, a non-native fungus that kills ash trees, is predicted to make an impact in the coming decades. This could change the appearance of One Tree Hill, especially on the northern slopes where ash has been one of the principal colonisers. One Tree Hill, the allotments and playing fields are part of a wider landscape, connected to Brenchley Gardens, Camberwell New Cemetery and then further by the railway sidings which are so wild and good for wildlife. Any wider landscape alterations outside One Tree Hill’s boundaries would impact on the species present. At the time of writing, plans to increase burial space along the boundary with Camberwell New Cemetery have led to a degree of unrest amongst local people. The same can be said for initial plans to return the Honor Oak Recreation Ground to its original plan of becoming an extension of Camberwell New Cemetery. But there lies the challenge for conservation in south London. The presence of a green space next door to One Tree Hill means that it is in better ecological health than if it were a car park, and cemeteries are often allowed to be a little more rough, ready and wild than manicured ‘green deserts’ that some parks can become. The key is for a landscape-scale vision for management and conservation as undertaken by London Wildlife Trust in nearby Dulwich. Likewise, the One Tree Hill allotments present a unique situation where a somewhat intensively managed area of food growing plots happens to support common lizard, a species that is uncommon in London, whilst One Tree Hill is now shorn of it. The Allotment Society deserve praise for allowing a buffer of woodland to remain between the two sites, and for showing an interest in wildlife, recognising the role the allotments can play in ensuring the wider landscape is rich and well managed.

From an ecological perspective, local tree planting should be reflective of the species which have been present in the area longest, namely: English oak (Quercus robur), sessile oak (Quercus patraea), field maple (Acer campestre), ash (Fraxinus excelsior), wild cherry (Prunus avium), hornbeam (Carpinus betulus), silver birch (Betula pendula), hazel (Corylus avellana), holly (Ilex bacciata), hawthorn (Crataegus monogyna) and blackthorn (Prunus spinosa). The plans for replanting at Camberwell New Cemetery match these suggestions, the intention there is noted and welcomed. Native trees are important because over millions of years invertebrates have evolved preferences and dependences on certain plant species, and their predators have developed preferences based on those insects. For the benefit of One Tree Hill and other local wildlife, a plan should be put in place to ensure native tree species are planted which notionally will act to extend the boundaries of One Tree Hill. Such long-term joined up thinking requires investment and patience, but it can be done cost effectively so time and money need not be an excuse to ignore the opportunity. There are many local people willing to help and their enthusiasm should be encouraged. To the garden warbler, arriving at One Tree Hill in spring all the way from Africa, geographical boundaries do not register. Local residents can make a difference by managing their gardens in a way that is reflective of the flora and fauna of One Tree Hill.