OAKS ON THE COMMON
English Oak (Quercus robur): The only native oak on the Common, the English oak rightly holds a special place in our culture, history, and hearts. It supports more life than any other native tree species in the UK. Here on the Common, nearly half our 4,000 trees of size are naturally seeded oaks.
Holm Oak (Q ilex) was introduced to the UK in the 1500s. Not as adapted as our native oaks, it supports plenty of wildlife and is the genus’ only evergreen species. Here on the Common they are now so prolific as to be almost invasive, having ‘escaped’ from the Old Cemetery where some were planted.
Turkey Oak (Quercus cerris) arrived in the UK in the 1735 and now impacts our native oak populations. It is of less value to wildlife, but much faster growing, and is a host of the knopper oak gall wasp.
American Red Oak (Q rubra): Just when this fast-growing North American native was introduced to the UK and by whom is a bit of a mystery. However, most authorities seem to agree that it was first cultivated in the UK by Philip Miller at the Chelsea Physic Garden in 1739 with an earlier date of 1724 given, although the source of this information is unclear. It certainly appears in seed box lists dating from 1744, sent as part of the famous partnership between early American plant collector John Bartram, the aforementioned Philip Miller, and Peter Collinson.
Although not as valuable to wildlife as our native oaks, it is still very popular with nesting birds, pollinators – and autumnal photographers! The ones you see on the Common and at Vine Road were all planted originally and there is also evidence of self-seeded saplings.
How old are our oaks? We estimate our oldest oaks at 150-200 years old, and would have grown up in open spaces, coinciding broadly the time grazing ceased. However most on the common are young: less than 75 years old. Paintings and early photos confirm the Common was almost bare of trees until well into the 20th Century.
How can we identify oaks?
The bark is brown, rough and especially on the trunk near the ground, deeply rutted. The outline shape is typically ‘square’, with outer branches reaching up almost as high as the central lead branch, but in denser woods the shape will have a tall trunk, often with dead side branches. This relates to how the trees have been planted and how they compete for light.
In Spring, the oak’s distinctive lobed leaf is one of the first young children learn to recognise. Later in the year come the familiar acorns (nowadays many may be deformed into wrinkly ‘knopper galls’ caused by a small solitary wasp). You may also see other galls. One of our most common – the marble gall – is particularly obvious, as it dries into a round brown ‘marble’ which hangs on the branch a long time. These galls used to be much prized as a source of dye for ink and are not harmful to the tree.
Like all plants, light from the sun is the food and energy source and oaks will do all they can to reach for it. In dense woodland, trunks grow straight and tall, making them good for timber. Places like the New Forest were created and managed to produce timber for ship building. Following the fire at York Minster in 2009, these were the only trees in the UK large enough to replace the ancient beams. Restoration had to wait for the timber to be cut and to dry naturally.
However, when there is no need to compete for light, the tree branches low and spreading – why waste energy? This results in perfect ‘climbing’ trees and there are about six here on the common. Generations of children have grown up with their favourite climbing tree, and in some cases now share these treasured experiences with children and grandchildren of their own.
The Oak and the Dragon is a wonderful interactive story based around our oldest oak, written by Sharon Morgan and read by Niamh Cusack as part of the OSO Bedtime in Barnes project
The value of our oaks: A healthy mature oak may have as many as 250,000 leaves that, through the wonder of photosynthesis, use the energy in sunlight to convert carbon dioxide and water to sugar and oxygen. Sequestration, the continual process of storing carbon, is a natural product of tree growth. Young trees absorb carbon more quickly, but older trees have greater storage capacity as well as being host to a greater number of species, so there is huge value in having mixed ages in a woodland. The economic value of trees is still being assessed but runs into tens of thousands of pounds each. In urban settings, where trees help mitigate the increasing impacts of climate change by improving air quality, absorbing harmful particulate matter and lowering temperatures, the value is likely to be far higher.
Doing so much good makes it hard to realise that trees can also be ‘weeds’ and may find themselves simply in the wrong place. Indeed, a tree is no more welcome in the acid grassland than a dandelion in a Wimbledon tennis court. Find out more about how and why we manage trees on the Common in this conservation update from Will.
Symbiosis and biodiversity: The English or Common oak is host to more invertebrates than any other tree species in the UK. In June/July, as caterpillars hatch, there may be as many as 110 different species of butterfly and moth living on oaks. This includes hairstreak butterflies, tortrix moth (with little green caterpillars that hang on silk threads to avoid predators), as well as oak beauty, brindled beauty, mottled umber, oak hook tip and many more.
A hazardous and unwelcome visitor is the oak processionary moth. Current recommended guidelines and information from the council are available here: Oak Processionary Moth Warning
Oaks grow easily from acorns – but there will have been many thousands of acorns for each single tree that reaches maturity. Did you know that squirrels take a nibble out of acorns before burying them which is certainly not helpful for germination? A lesser-known and interesting partnership is with Jays. These birds love to stash acorns to feed on in winter. They often do this out in the open meadows, some distance from the parent tree. Through winter, they do not always find their stash and if mice and other animals also miss them, then they will germinate, and you may get a sapling up to half a mile away from its parent. Indeed, this is how a forest can ‘walk’ over the centuries, notably in response to climate changes. It is evolution and adaptation at work, with the trees in the best locations doing better than those that find the going tough.
M Hildesley; S Morgan. Images A Wilson unless stated. 13 April 2020. Updated June 2021.
References and Further Reading:
Bridgeman Karen; Painshill Park; pers comm 17.04.2020
Wohlleben, P, Flannery T, Billinghurst, J, 2016. The Hidden Life of Trees. Vancouver Canada: David Suzuki Institute