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Trees on The Common: Chestnut

Horse Chestnut Trees in Flower

Trees on The Common: Chestnut

This Week finally brought some much needed rain. Given the wet winter we had, that was a sentence I did not expect to write around May Day! We can now look forward to an explosion of growth as moisture and warmth provide optimal conditions. It has been a week to ponder changes in climate: heavy thunder clouds displacing sweet April showers, trees in leaf weeks ahead of norm – and everywhere uncertainty about what our ‘new norm’ may be. And yet …. the carpet of May blossoms reminds us of the origins of confetti, traditions we love and for me – the wedding of a nephew I should have been celebrating …instead of preparing a new composting area in my garden!

Horse Chestnut Trees in FlowerThere are two types of Chestnut on Barnes Common: Horse Chestnuts (three species) and Sweet Chestnut (one species).

Horse Chestnut (Aesculus hippocastanum) Flowering ‘candles’ of white flowers, conkers in prickly shells, sticky buds and large distinctive leaves – the ‘conker tree’ is one of the first children learn to love. Native to the Balkan peninsula, it was introduced in 1616. Most, if not all, of our 200+ mature horse chestnuts on the common were planted, largely in avenues along roads and footpaths. The soft, weak wood means that large branches in mature trees can snap off the trunk at any time of year, even in healthy trees. They do not take kindly to pruning, with rot setting in very easily and this makes it difficult to manage mature trees.

Indian Horse Chestnut (A indica) arrived in the UK from the Himalayas in the mid-19th century. We have one planted near the reedbed. It has similar palm-like leaves (although a deep red when first bursting), the flower candles come a bit later than A hippocastanum and the conkers are darker, with a smooth casing.  This species is increasingly popular with gardeners and park superintendents as they appear resistant to the diseases attacking our traditional horse chestnut.

Red Horse Chestnut (A x carnea) is a hybrid cross between horse chestnut and the American ‘Red Buckeye’. Easily distinguished by its red ‘candles’ (flowers), unlike many hybrids it can breed true from seed. There is an example on Vine Road near the Upper Richmond Road.

Sweet Chestnut (Castanea sativa) is native to Europe and completely unrelated to Horse Chestnuts. More closely related to Oak and Beech, it was probably introduced to Britain by the Romans.  The leaves are individual, long and toothed. The flowers appear as catkins and the fruit is conker-like but in a very prickly case.  The bark in a young tree is silvery and the first fissures appear vertically.  With increasing age the bark becomes browner and the fissures more pronounced, flattening into a distinctive spiral around the tree, which is most pronounced nearest the tree’s base (really helpful for winter identification – as will be the spent casings all around the tree).  The fruit of sweet chestnut is edible but should not be foraged as it is such an important autumn feed for wildlife (and in Richmond Park for the deer).

Food value: Sweet Chestnut is a much more useful tree to humans than horse chestnut, which is largely ornamental.  Before potatoes were discovered in America and brought back to Europe, chestnuts were an important source of carbohydrate in the human diet, since they could be stored for long periods and cooked in many ways. Today it is a supplement rather than a mainstay, but the history survives in our own midwinter feasting tradition, as an ingredient often used in stuffing for the Christmas Turkey, harking back to times when roasted birds were a relatively rare delicacy and would be ‘padded out’ with stuffing.  Roasted chestnuts are still popular as a street snack in midwinter (especially in New York).  Chestnuts preserved in sugar (marrons glacées) are also a great delicacy.

Other uses: Sweet Chestnut coppices well, with several stems re-growth with each coppicing.  The wood grows quickly and straight, so is easily ‘cleaved’ – split rather than sawn. Cleaving helps keep the cell structure within the wood intact, so the resulting wood will not rot as quickly as sawn timber.  The coppiced trunks of sweet chestnut are used to make split chestnut fencing, as well as post and rail fencing. The main plantations are in Sussex and Kent and the railings are known as ‘Sussex fencing’ (examples can be seen in Richmond Park protecting old oak trees).  On the Common we have one fully mature sweet chestnut and occasional immature trees, mostly planted around 25 years ago.  One of our ambitions is to grow and coppice more chestnut so we can create more of our own posts and rails, adding to our range of traditional woodland crafts and management.

Diseases: Sweet Chestnut blight has severely affected the USA, parts of Europe and has arrived on these shores, so we need to be especially vigilant.

Horse Chestnuts are under double attack: first by a micro-moth which lays its eggs on the leaves to provide food for the tiny grubs when hatched, causing leaves to soon turn blotchy, often appearing completely autumnal by August. Although some trees may have a second set of leaves, the tree is unable to photosynthesise efficiently and this results in reduced vigour and stress. Almost all our horse chestnuts are showing distinct signs (although it may not appear so in Spring, before the first round of eggs are laid on and hatch in the new leaves). Secondly, horse chestnuts are prone to bleeding canker, a fungal attack which can prove fatal, especially in mature trees. Trees live in symbiosis with fungi and bacteria which helps the roots draw in nutrients. However, it seems that when these fungi sense the tree is under stress, they will fruit in order to spread to other trees. This takes enormous energy, gained by feeding on the lignin in the heartwood, which in turn significantly weakens the core strength of the tree and leaves it vulnerable to attack by insects and other rots. Interestingly some hollowed out trees survive because there is not enough food left for the fungus to achieve fructification. Unless Nature finds its own cure, we are likely to lose most of our 210 mature horse chestnuts in the next few years, (current rate of loss is 6 to 10 annually). We are in discussions with the Council about long term planning – with the aim of conserving a predominantly native broad leaf woodland alongside the grassland and wetland habitats, naturally spaced and using locally sourced saplings where we cannot transplant from the Common itself.

The pathology of these diseases is complex, and there are interesting links at the end of this article if you would like more in-depth detail.

Conkers Children love to collect the attractive shiny fruits and for centuries conkers were a popular children’s game in the autumn, Health & Safety permitting.  The rules were simple: thread a conker on a string, challenge your friend and take turns to break his or her conker off its string with your own. The winner added the score of the losing conker to their own. (Cheats would gently bake their conker or soak it in vinegar until it was hard). Bruised knuckles were common, but damage was less than many another game of my youth.

Can you eat conkers?  No.  Conkers contain chemical collections that are toxic for humans and many animals, although deer and boar can break down these down and digest conkers safely.  This may be why some people put a few conkers in their cupboards as a deterrent to spiders and moths but I would not rely on this.

Conkers in the Great War:  In the autumn 1917 a call went out for children to collect as many horse chestnuts and acorns as possible and they were paid 7/6d for a hundredweight, a substantial sum in those days.  Why? Cordite had replaced black gunpowder as the main propellant in armaments and prior to 1915 mainly came from America.  Manchester chemist Chaim Weizmann invented a new process, but ingredients still had to be imported. The process was adapted to use the starch of conkers and acorns.  On Churchill’s orders, a special plant was built in Holton Heath, Dorset to undertake the fermentation and cordite manufacture – parts of which remain today as listed buildings.

Next Week: Ash

MH 4th May 2020

Image credits: M Hildesley

Historic England – Conkers and the Great War

Sweet Chestnuts under attack Forest

Bleeding Canker in Horse Chestnuts Forest

Duncan Slater: Recovery from Bleeding Canker