30 September 2012

Major Threat to Ash Trees in the UK

ash dieback leaves

Given my annoyance with the ash tree that ‘just won’t die’ in Garden65 I thought I’d take a closer look at the threat to ash trees in the UK that has been recently announced in the news.

The Forestry Commission has produced a page of information about the disease and what measures are being taken to tackle it.

If is officially being called ‘Chalara dieback of ash’, or ‘ash dieback’. Caused by a fungus, Chalara fraxinea, the symptoms are leaf loss, brittle twigs, black spot and canker on the bark, followed by the dieback of the crown. Eventually the whole tree dies. Young trees are most susceptible. Mature trees may be able to withstand a season or two of this onslaught but will succumb in the end. All types of ash trees are affected especially the common ash, Fraxinus excelsior.

The disease has been decimating Europe for last 9 years, with many countries losing the majority of their ash trees. Denmark has lost 90%, Lithuania 60%, Poland 80%. There is a huge worry that this too will happen to Britain’s trees. As the Forestry Commission says, ‘We have no reason to believe that the consequences of its entering the natural environment in Britain would be any less serious.’

Unfortunately the infection has already arrived. In February this year it was found on trees in a nursery in Buckinghamshire that had imported plants from the Netherlands. Some trees had already been sold to 90 customers via mail order. The authorities have followed these up and ordered the destruction of them all. However other infected trees have been discovered in a new planting scheme in a Leicester car park, and various other new plantings even as far as Glasgow.

The problem is that it is not an EU regulated pathogen (because it is so common there) so trees can be imported from the continent without any restrictions or checks on whether the plants are carriers or not. The Forestry Commission and the Food & Environment Research Agency (Fera) (ie. the government) has started a consultation on whether emergency quarantine measures should be imposed to prevent importation, but any legislation to do that would only come into being in a few months time. The Horticultural Trades Association (HTA), the trade association for horticultural industries such as nurseries and garden centres, has recently suggested a voluntary moratorium on imports.

Naturally organisations like The Woodland Trust are outraged by this lack of decisive action. Interestingly I heard of this threat to our ash trees from the Trust publicising their anger. I’m not sure the Forestry Commission have made a general announcement to the public. The Trust points out the ash is the most important broadleaved tree in the UK after oak and birch (another authority has it as the 4th most important). If our native ash is affected as much as those in other countries our woodlands would be changed dramatically.

Unfortunately, as is the way in this modern commercial world, money muddies the water. The HTA has asked for compensation for tree owners who have to cut diseased trees down. Sensibly the Commission has replied:

“It has been the position of successive UK Governments that the risks from plant pests and diseases, like other risks, are part of routine business management, and that the risk should therefore be borne by the businesses concerned. As such, compensation from public resources is not appropriate. It is considered that the limited public resources available are better allocated to surveillance, research and management of pests and diseases to help mitigate any impact on businesses associated with the growing and management of trees.”

A recent article (20th September) in Horticultural Week, a magazine “by horticulturalists for horticulturalists” further explored the monetary concerns of this impending tragedy. The disease is notifiable, but since the trees die gradually without branches suddenly falling off there is a reduced danger to the public. Tree owners (and this includes councils) may then be tempted not to spend money cutting down the tree and disposing of it in the proper controlled way. The article suggests many diseased trees will not be dealt with.

Horticultural Week then gleefully says testing trees for evidence of dieback may be a new lucrative income stream for tree firms!

In the more measured environment of Nordic academia Copenhagen University has been studying the genetics of the disease. They have discovered 5% of ash trees have a high resistance to it, and that resistance is inherited by seedlings of those trees, although only 1-3% produce healthy offspring.
The Danish authorities are dealing with the situation by logging mature trees, not only to prevent the spread of the disease but to harvest the timber before the quality deteriorates. Scientists are trying to set up a system of testing for resistance before they get cut down. Seeds and grafts are being preserved with the aim of restoring the viability of the ash species in the future. They estimate this will be possible in over 10 years time.

The good news is that the ash tree WILL recover, but it will take time.

I wonder what positive steps our authorities are going to take?

Meanwhile I’m keeping an eye on my ash – I’m sure it’s one of the 5%.


Forestry Commission
Forestry Commission
The Woodland Trust
Copenhagen University
The Horticultural Week won't let me see the article anymore, so boo to them I'm not going to link to them. Ha!
Source of images

28 September 2012

An Exotic Visitor

Sally popped in the other day.

She wondered about the fruit bat that was hanging from the washing line.

I had to confess it wasn't a new exotic pet, but the peg bag, well past its best.

I think it looks like an oven ready chicken.

26 September 2012

After The Deluge

cold wet bee after rain

After two days of constant rain I ventured out into the garden with the intention of taking arty shots of raindrops. Instead I witnessed a tragedy no doubt being repeated throughout the country.

cold wet bee
This poor bee, with his matted teddy bear fur and school boy fringe plastered to his forehead, was sat violently shivering in the weak morning light.

A garden spider had got to work weaving today's web. She was too busy to give him any attention (just as well perhaps).

I kept snapping away, trying to get him in focus (and failing), looking for good angles, and then compassion whispered in my ear. I felt like a war reporter taking photographs of someone struggling for life. There is a dilemma between witnessing the event so others can see the truth, and putting down the camera to help.

Admittedly this tiny moment was not as important as some atrocity of the human world. It was only a cold bee. But some part of me felt bad.

In the end I did try to encourage him onto a saucer of sugar water, but in doing so knocked him off his perch into the shrubs below and lost him. Now I feel even worse!

Arty shots:

See the reflection in the rain drop

(I get confused - are bees female, male or neither?)

24 September 2012

22 September 2012

Spiders! Orb Weavers

Now here is a spider with a greater sense of order than the previous sheet weaver.

She is a common garden spider (Araneus diadematus), recognised by the cross over her shoulders.

And here's something I didn't realise before ... orb spiders hang upside down. Nip outside and have a quick look at your spiders ... see? upside down. Wonder why.

There is a really interesting MSc thesis by Thomas Hellelberg of Aarhus university on the web [see what I've done there?] on how garden spiders build their webs. If you want to know more about it I strongly recommend you have a look.

Orb webs have distinct elements:

Which are evident in this image I've turned to black and white and inverted:

A     the hub
B     the free sector
C     the capture spiral
D     the frame
E     radii
F     spiral turns
G     mesh size
H     reverses

Scientists divide the web into 4 quadrants (I don't think the spiders do this, having not gone to school to study geometry), and it seems webs are consistently larger in the southern quarter with a more even mesh size and more radii in that zone. And this does seem to be the case in this web. 

I wonder if this is why the spiders sit facing downwards - prey is more likely to be caught in the better constructed southern area. Maybe I should ask Thomas.

20 September 2012

Spiders! Sheet Weavers

Linyphia triangularis Sheet weaver spider

I'm sorry, but we have to face it, this is the spider season, and it would be remiss of me not to say something about them.

This fine-legged lady hanging upside down from her web is, I think, Linyphia triangularis, a sheet weaver spider.

We can assume she has little understanding of geometry, and doesn’t care for the artistry of perfect spirals. Aesthetics are not her priority. As long as the web is fit for purpose she doesn’t worry about the look of it. Some sheet weavers add a funnel of silk from which they hide, but this one is confident enough to hang from the middle of her web and wait for those foolish flies to get entangled.

In truth there is some method to her madness. Above the flat sheet of the main web she has built a tangle of long threads, which you can see better in the image to the right.

These are the ones that trap the flies. Some experts say they also serve to protect her from birds coming from above.

She's no fool.

Here's a neat graph from Britishspiders that clearly highlights this time of year as the spider season. It shows the frequency of adult Linyphia triangularis sightings.

And, yes, looking the garden, I can confirm its accuracy.

18 September 2012

Oxen-born Bees - Fact and Legend

hoverfly eristalis tenax wing veins

Front cover of Royal Entomological Society handbook

diagram of hoverfly wing veins. Vena Spuria

Baron Karl-Robert von Osten-Sacken (1828, St. Petersburg –1906, Heidelberg) was a Russian diplomat and entomologist. He served as the Russian consul general in New York during the American Civil War, living in the United States from 1856 to 1877.

15 September 2012

Robot Squirrel

grey squirrel with red eye

Local squirrel with dreams of auditioning for Schwarzenegger's new Terminator film.

There Are No Cranesbills in Yorkshire

According to the charity Plantlife 10 species of wildflower have become extinct in Britain since the 1950s.

Land management changes since then are the cause. Industrial scale farming means there are fewer proper hedges and untouched field margins, and of course the increased use of herbicides plays a part. Since the war 97% of wild flower meadows have been lost, with a third of all plant species in Britain currently in danger of extinction.

Let’s repeat that statistic – a third of ALL plant species, not just the pretty flowers, but the ferns and mosses and lichens, grasses, shrubs and trees are ‘in danger of’ extinction.

And let’s face it, bar major changes in the economic, political or population spheres, that ‘in danger of’ means ‘will become’.

On the county scale the situation is stark. Middlesex has lost 76 species in the last 40 years, Warwickshire has lost 74 species since 1970. Even the subject of the last post, the wood cranesbill, has disappeared from Yorkshire.

Plantlife will publish a report next month. Not a light read I should think.

I’ve whacked up a little montage of the 10 lost plants.

Something that struck me while I did was that this impoverishment is not only in terms of biodiversity, but also language. In the last post I wondered how the cranesbill got its name. How did the Interrupted Brome or Summer Lady’s Tresses get theirs? Isn’t that interesting – it’s Summer Lady not Summer Ladies? Who was the summer lady?

It’s sad to think there will no longer be anything new in Britain in need of a name.

Information from Telegraph article

Image of Hawkweed from Kingsdowner blog , saxifrage from this Tumblr blog, other images from newspapers and wiki.

13 September 2012

The Romance and Science of Cranesbills

While chasing Sheila the Shield Bug around the geraniums I noticed the flower’s ornate seed heads. That lovely curl wouldn’t look amiss on an iron gate, or an elegant art nouveau copper lamp. My dream ‘Arts and Crafts mansion’ (doesn’t everyone have one?) would definitely have shapes like that somewhere in it.

In reality what is happening here is very interesting.

Unlike the daisies we looked at before the geranium doesn't lie back once the seeds have been generated and passively let wind or animals disperse them. It's involvement is more active.

The seeds themselves form against a long column, or 'beak', that grows up from the old flower head. When they are ripe the beak splits and springs each seed upwards. The force of this movement should be enough to fling the seeds a distance away from the main plant.

Which doesn't seem to have happened in the above picture.

 Here are a couple of diagrams that explain my understanding of the action.

Having dealt with the science bit we can return to the world of imagination.

As I'm sure you are aware the other name for geraniums is cranesbill. I think the pink ones growing in Garden65 are wood cranesbill (Geranium sylvaticum). And why are they called cranesbill? Because that column that flings the seeds away reminded someone sometime of a 'crane's bill'. It's not called a beak for nothing.


I wonder who originally thought of that connection. Was it some peasant walking in a woodland in late summer who picked a geranium, saw the shape of the seed head, then glanced up over the nearby marshy fields towards a group of cranes and thought, "That looks like that. From now on I'll call this plant 'cranesbill'"? Would it happen like that? Or maybe the scientist who formally identified the plant and added it to his grand taxonomy scheme whimsically gave it an amusing name. I wonder what it is called in other countries.

12 September 2012

Sheila The Shield Bug Survives!

Shieldbug nymph

I'm pleased to report that contrary to my previous fatalistic prediction for Sheila The Shield Bug Nymph she has actually survived the summer. Of course, this could be one of her siblings, but let's remain hopeful.

As Shield Bugs grow they don't go through a larval stage but gradually morph into their adult shape. Each step in the process is called an instar.

When we first met our Sheila she was in her first instar:

Earlier in the year I saw adult Shield Bugs trundling along the branches of one of the Alemanchiers. Sheila was found on a mint leaf under this tree, so I am guessing the tree rather than the mint is her natural habitat, and that she had fallen down from it. Another piece of evidence in this hypothesis is that she is a Hawthorn Shield Bug. There is a young hawthorn a couple of metres away which has indeed been munched to oblivion, which makes me think trees or at least shrubs are her normal playground.

However, precisely two months later here she is as a teenager (or 'young adult' as my 17 year old son insists) in her fifth and final instar running gaily through the geraniums under the same Alemanchier.

5th instar shield bug

I have a soft spot for Shield Bugs because they remind me of rhinoceroses or triceratopses, so I'm glad to see her survive, but this warm feeling may change when I found out what she is actually eating in my garden.

Here is a fantastic illustration of the various instars Hawthorn SBs go through.

The source for this is British Bugs, but the illustrator is Ashley Wood who has many other bug drawings on her Flickr site which is well worth a look.

10 September 2012

A Camera-less Photograph

camera-less photo
The resultant photograph of leaves laid directly onto photographic paper

Years ago I did a City & Guilds photography course. I didn't realise it then but I was immensely privileged to be able to use the college's darkrooms to learn the basic principles of photography.

If you think about it a photograph is a record of light, not the objects in front of the viewfinder. It is light reflected off the objects that enters the lens of the camera, either film or digital (or phone!), and changes something within the camera. In an old fashioned film camera the light affects chemicals on the film; in a digital camera the reaction is electrical rather than chemical.

We gardeners understand the magic of light. It makes plants grow, but also manages to kill them by simply not being available or dehydrating them by shining too powerfully for too long. And now of course autumn is ‘in the air’. How do we know that when there is, as yet, no discernible lowering of temperature? It is because the light has changed. The Earth is tilting and we are still animal enough to sense it.

Using light sensitive photographic paper it is possible to witness light in action second by second.

Initial Set Up

And the reaction really is quick. Even as I was taking the paper out into the garden it began to change colour. Chemical changes turned the white paper blue. Quickly I lay on a fern, ivy and geranium leaves, and an helenium flower. The idea was to record their shapes by preventing light hitting the paper, but so sensitive are the chemicals that their shadows would also be recorded.

Close Up Chemical Changes Around A Leaf

Within in a minute or so the blue changed to a pinky brown. When these papers are used properly in a darkroom and exposed to the intense light from an enlarger they produce the black and subtle greys of a typical black and white photograph. But out in the open light from the sun is not strong enough to create these changes.

Half An Hour Later

Remember the sun moves through the sky so the light hitting the paper doesn't come from one direction. If you look closely at the above image you can see newly exposed areas around leaf edges. Because of this a crisp outline of the shapes isn't recorded, but I like that. Somehow it makes the shapes more alive and three dimensional.

Unfortunately I haven't got the chemicals to stop the chemical process continuing. Normally you would put the paper into a bath of fixative and then the photograph would last years and years without changing. But this one will transform over time endlessly until, I suppose, the leaves will disappear. At the moment it is on the wall by my computer. The blue colours have gone completely but the plants are still recognisable.

This photograph is an alive thing. It is not a recording of one moment in time, but a witness of Life itself (if you see what I mean!).