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Posts tagged ‘oak’

Field oak with rooks

April 18, 2013

Gabriel Hemery

Field oak (Quercus robur) and rooks by Sarah Simblet

Field oak (Quercus robur) and rooks by Sarah Simblet

Photograph (low quality) of a completed drawing by Sarah Simblet for The New Sylva: Field Oak (Quercus robur) and rooks.

Oak processionary moth (OPM) – a disaster already happening


Every now and then in life you gain sudden clarity of vision about an issue; perhaps triggered by listening to someone erudite, reading something written with super clarity, or seeing it with your own eyes.  In my case it is the latter and I’m worried – super worried in fact. I am not prone to exaggeration.


Deer at rest in Richmond Park. Notice the horizontal browse line of the trees.

I recently visited Richmond Park, the largest of London’s Royal Parks. It is a vibrant place full of ancient trees, home to several herds of Red Deer, and it teems with joggers, dog walkers and families. Around it on all sides is the highrise metropolis of London including Wimbledon, Putney, Richmond and Roehampton. In a few weeks it will be host to the Olympic cycling road race. Most visitors scarcely notice the metal fencing and red tape around the occasional oak tree; presuming probably that the tree may have a dangerous branch or needs extra protection from the browsing deer. But they would be mistaken.


OPM leaf damage on a young oak tree. Other species of caterpillar can cause similar defoliation but signs of silk among the stripped leaf veins should start to raise alarm bells and a search for nests on the bark should be undertaken in July.

I saw with my own eyes the oak trees of Richmond Park infested with the caterpillars of the oak processionary moth (OPM) Thaumetopoea processionea. The caterpillars can cause serious damage to trees by defoliating entire canopies but this is a minor problem in comparison to their effect on human health. The caterpillars of the third to sixth instars have poisonous hairs or setae that carry a toxin that can cause serious irritation to the skin, eyes, nose and throat of humans and other animals.  If inhaled they can cause respiratory distress, asthma and even anaphylactic shock.


An oak tree under treatment for OPM attracts public interest in Richmond Park. The groundsman directs his colleague on a telescopic platform – the only safe way for a worker to gain access to the upper canopy where the caterpillars build their nests in July.


OPM control demands rigorous personal protective measures


Removing an OPM nest in the upper canopy of an oak tree. Standing on a telescopic platform the worker inverts a plastic bag to encase the nest before scrapping it off. He wears full protective gear including suit, gloves, facemask and goggles.


An OPM nest safely bagged

The human health danger is scary in its own right but it is the consequences of the increasing spread of OPM that is my real concern. Three years ago the authorities at Richmond Park spent £50,000 in one season trying to control the pest but costs have been doubling every year, year on year! A decision was taken last year by all those concerned with OPM in London that eradication was not an option; instead aiming for containment. Meanwhile the moth continues to be found in an ever-increasing range within Greater London. An outbreak in Sheffield was successfully controlled, while a population in Pangbourne near Reading evaded extinction in 2011 and is currently being retreated. How long before the various authorities decide that it is no longer worth spending a six figure sum trying in vain to control OPM when all around them trees in private gardens are going uninspected by the unaware general public? Sadly it may take a child blinded or even a death being reported in the red tops, like the Daily Mail, before notice is taken. This is not a forestry problem – it is a human health problem!


A small OPM nest – can you spot it? It is visible on the border between the green-tinged and brown bark.

OPM nest on a large oak branch

OPM nest on a large oak branch. This one is easy to spot. Click on the image to view in larger scale and you will be able to see the silk trail left by the caterpillars as they processed along a smaller branch (visible left-hand side) en route to form their nest.

OPM nest on a small oak branch

OPM nest on a small oak branch. You might need binoculars to spot this one from the ground


Close-up view of an OPM nest

While huge amounts of public money are being spent on attempts to control OPM with little effect, the pest is not yet at large among private gardens and larger forests.  When, and it is surely ‘when’ and not ‘if’, OPM becomes widespread on private land then it will be the landowners that will be required by law (under the Plant Health (England) Order 2005) to report their presence and pay for their control. I can’t imagine any owner of an oak tree infested with OPM being pleased when required to spend up to £1,000 per tree. Forests in Holland and Germany have been so badly infected that they become out-of-bounds; the timber unusable for several years as the toxic hairs remain dangerously potent even on the forest floor.

I fear that OPM is a huge elephant in the room that everyone is wishing would go away. But, it is still early days in England, and if a German or Dutch arboriculturist were to see the extent of OPM in Britain they would surely urge us to try harder: to go for eradication across all of London rather than to give in now. Yes it will be expensive. Yes it will need co-operation between lots of different authorities. Yes the public will have to be involved too and be encouraged to report OPM in their gardens. Ignoring OPM is not an option – its spread is a disaster already happening – soon impacting our gardens, parks and forests across England unless action is taken urgently.

Further information on the Oak Processionary Moth (OPM)

Oak Processionary Moth – management implications

A looming threat to man and tree – a post I wrote in 2011

More information on OPM from Forest Research

Drawing the magical oaks of Wistman’s Wood

March 30, 2012

Gabriel Hemery

The authors visited Devon recently on the search for a number of trees and forestscapes for The New Sylva. Followers of The New Sylva on Twitter (@newsylva) will know that our first stop was the ancient oaks of Wistman’s Wood on Dartmoor, followed by a successful search for one of Britain’s rarest trees; the Plymouth pear Pyrus cordata, found appropriately in the city of Plymouth.

The trees of Wistman’s Wood are almost entirely pedunculate oaks Quercus robur, with scattered rowan Sorbus aucuparia and holly Ilex aquilifolium. The oaks are deformed and dwarfed by the exposure and altitude (400m), their branches and stems festooned with mosses and bearded lichens, and clumps of polypody ferns. The granite boulders, which protect the trees from grazing sheep, are clad completely in a carpet of mosses. It is a magical place.

Sarah Simblet drawing in Wistmans Wood

Sarah Simblet drawing in Wistman’s Wood for The New Sylva

Sarah Simblet spent over five hours composing a drawing of the magical wood. Working with a hard pencil (3H), so as not to permanently stain the paper, she developed the composition that she will later work up in pen and ink at her studio with the help of many photographs. Every trace of pencil will then be erased in readiness for scanning the drawing so that it can included in The New Sylva.

The Wistman’s Wood forestscape will contrast greatly with another oak scene that we have planned to illustrate one of the greatest productive oak forests in Europe.

Winter Ash Haiku

January 6, 2012

Gabriel Hemery

Winter Ash Haiku

Afterlife tool and spoke
Winter ash gale bend and yield
Oak a merest nod

Gabriel Hemery

During the recent winter gales in England I was inspired to write a Haiku poem. The amazing flexibility of the ash Fraxinus excelsior tree means that its wood is widely used in tool handles, sporting goods such as hockey sticks, and in the spokes of wooden wheels. In this short film made amidst a woodland gale, an ash tree waves and yields by amazing degrees in the gusting wind. Nearby (just visible distant far left) a stoic English oak Quercus robur tree hardly moves.

Gabriel Hemery

Oaks in snow

oak log in snow

Wishing all my readers a very Happy Christmas


a fruitful New Year

Gabriel Hemery

Raining acorns

September 30, 2011

Gabriel Hemery

Acorns and dog walking
Acorns and dog walking

Walking my dog in an acorn shower

At this time of year our woodlands are spectacular; seemingly a palette containing every colour ranging from the oranges and russet browns of fallen oak leaves, the red of hawthorn berries, to psychedelic pinks in Spindle fruits. Observe closely and your senses can be entertained in other ways too. During a walk through a local woodland with my dog, I was enthralled by a percussion performance by a stand of oak trees .. it was raining acorns.

I recorded the acorn music – click on the play button above to listen.

Listen carefully and you will hear three gusts of wind; each appearing as a rising crescendo of rustling approaching through the woodland. With each gust the shower of acorns increases. I love the way that the falling acorns make three distinct sounds: crashing through the leaves of the canopy, tonking on the branches that sometime block their way, and thudding as they hit the ground.  Some fall very close to my recording equipment too!

It seems that 2011 is a mast year for oak, at least in parts of southern Britain. Oak trees produce acorns every year but every four to seven years they produce an extra heavy crop.  These are called mast years. There is still plenty of debate as to why trees behave in this way: it could be to do with water availability, temperature (in winter or spring), lack of frost during flowering or other reasons (see this scientific paper). We know that the extra effort put into producing so much seed can reduce the amount that a tree grows that year. Here is an interesting piece of work I came across, called dendromastecology, that provides evidence about the tradeoff between incremental tree growth and reproductive effort.

My walk left me wondering, along the lines of a popular saying, whether:

If an acorn falls in a forest,

And no-one is around to hear it,

Does it make a sound?

Gabriel Hemery

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