Nov 04 2019

White lab coats, axes and beetles!

On Wednesday 30th October, I joined nine Observatree volunteers at Forest Research’s Northern Research Station, south of Edinburgh, for a sharing and mentoring day.


Charlotte Armitage, who manages this volunteer role, set up the event with Hugh Clayden from Scottish Forestry, April Armstrong and Katy Dainton from Forest Research.  April’s area of specialism is tree diseases, whereas Katy focuses on pests such as the Great spruce bark beetle (Dendroctonus micans).


First of all we all had a go at evaluating some completed Observatree reports, to get a feel of what constitutes ‘good data’ and where incomplete reports can be a problem.


Evaluating Observatree reports for data quality


Following on from this we heard from Jim Pratt, a distinguished forester with a lifetime career with the Forestry Commission. His claim to fame, amongst other things, is that he was the first person to identify Dutch Elm Disease in the UK, on the Isle of Dogs.   He described the occasion when he first spotted a huge old diseased elm, bright crimson in colour; he’d never seen anything like it.  He attributed the arrival of the disease to be from beetles able to survive in containers on ships arriving into ports around the Isle of Dogs.


Jim Pratt’s inspriring talk about his life as a forestry pathlogist and about the ash tree.


Jim was Head of  Pathology at Forest Research for many years, and has 50 papers about pests and diseases after his name.  He retired in 2002, but is still active, particularly in lobbying MSPs and our UK governments about their obligations to protecting our woodlands from further pests and disease threats and damage.


His talk at out event, entitled “Ash Flowering: one thing leads to another”, was a fascinating story of his journey of discovery about ash trees enabled by his meticulous photography of two ash trees in his garden, every day for several years.  One tree was female and one male, and his close observations enabled him to observe how the two trees grew at different rates, and how, for example, the female tree’s growth rate was curbed after heavy mast years.  The female tree also suffered defoliation after heavy mast years.  This could mean that female trees might be more susceptible to Ash Die-back (Chalara), although he wasn’t certain whether the heavy mast was a result / symptom of stress, or indeed a factor in causing stress to the tree…a bit of a chicken and an egg situation!


He also suggested that as male ash buds and stems tend to be less fissured and knobbly than female stems, that this also might make female trees more disease susceptible, as pathogens have more to grab hold of on female trees!


The difference between male and female ash buds

Differential growth rates of male and female ash stems…female growth is more erratic.



He talked about how close observation, and over a long time, is so important, and how Observatree volunteers so well placed to do this; their role is vital.  Trees, diseases and pests change and evolve over time, so it’s so important to keep observing. Ash trees, for example, can be female, male or hermaphrodite, but can also have male parts on female flowers and vice versa, or even differences in gender depending upon the height up the stem, and also change sex over time.


Male parts on female flowers and female parts on male flowers!


He talked abut the massive occurance that producing seeds is for the female tree / female parts of a tree.  Samaras are the seed bearing bodies and these are held on the tree until they are mature by strong pedicels.  In gales of, say 50mph or more, the pedicels move in a way that the samaras cluster together to give increased strength against blowing away prematurely.


There are over 1,000 samaras in a single tree, with 100 or so seeds in each samara, so over 100,000 seeds in each tree, weighing 10kg or more.  This is 2-3 times more than the weight put on by a tree each year, so has a significant impact on the amount of energy the tree has to expend annually.  This is why trees have some years where they don’t produce any fruit, and indeed may not produce as many leaves either.


He also talked about how this erratic growth of female trees means that timber from male ash trees is more likely to be stronger and better for making furniture etc.


Jim also told us about historical uses of ash.  It was one of the most widely used timbers in neolithic times, as it is one of the best shock absorbers, so was invaluable for axe handles.  It is second only to hickory for its shock absorbing properties, but of course we don’t have hickory in this country.


Ash has been used since neolithic times for axe handles


Ash was coppiced in Scotland as far back s mesolithic times, and into the neolithic and bronze age. He pointed out that archaeologists are, in his experience, far less interested in handles than the blade of an implement, which he thinks is a shame!


Ash was also used in the UK by the Romans, in spear handles and other weapons and tools.  He pointed out that 24 million stones formed Hadrian’s Wall, which all had to be transported to the site, and that ash was used to make carts to transport them.  6-7 million tonnes of material was shifted by 7,000 men in 10 years to make the wall, so that was a lot of ash.  He showed an image of a roman wheel, incredibly skillfully made by bending the ash using heat and steam.  These wheels can be seen in the National Museum of Scotland.  Apparently there is only one person in Scotland who still continues this skill.


Roman cart wheels made using bent ash wood


In WW2, ash was used in combination with sitka spruce and plywood to build fighter planes, ash being used in areas of the structure subject to high stress, for example wing tips.  The Miles M20 was one example, able to fly at 500mph in the late 1930s!


The Miles M20 was a wartime plane made using ash for part of the structure prone to high tensile stress


Ash is still being used today for specialist uses, for example to build Morgan cars, for tennis rackets, table tops, hurley sticks, floorboards and so on.


Jim is curious to know if historically male trees were selected for use, and if therefore this has had a long term impact upon our ash population.


He’s also curious to know just how much more female trees are prone to Chalara, and if coppicing might be a way of keeping some trees disease-free.


Jim finished off by saying that we must all be vigilant.  A symptom on a tree that isn’t listed as a symptom might still be really important; it might be a new disease or an existing disease evolving and presenting in a different way. He sees the Observatree volunteer role as an incredibly important one, and that for it to be even more useful it needs to continue over the long term.  He pointed out how important it is to publish the Observatree data and findings in order for other researchers, across the whole of Europe and beyond, to follow on from what we find!


Lunch followed Jim’s inspiring talk, and then we donned white coats for a visit to the lab where April and Katy carry out their research.


April showed us an infected ash branch, and demonstrated how to take a helpful sample for diagnostics and investigation.  V-shaped lesions occur at the frontline of the spread of Chalara up a stem, and it is at the point of this lesion that a sample should be taken, and also from further up where the infection will also be spreading into live tissue. 


April told us of their work to sample and research the genetics of Chalara


Cutting a sample of Chalara infected ash

Cutting the sample from the border between diseased and un-diseased tissue

V-shaped lesion is a classic Chalara symptom

The sample is grown on in a petri dish

Several techniques for genetic testing are used to identify and analyse the Chalara genes.



Finally Katy showed us a live Spruce bark beetle, and some live Rhizophagus grandis beetles, which is the natural predator of the Spruce bark beetle.  R. grandis predates solely on great spruce bark beetles, and it has an extraordinary ability to locate them, even when there might be only a few infested trees.  R. grandis isn’t, however, moving as fast across the country as fast as its prey, hence the need to give it a helping hand by introducing it wherever an outbreak occurs.  The predator reduces the impact in timber crops from 10% loss to negligible.


Spruce bark beetle larvae

A live Spruce bark beetle….apparently they give them names in the lab!

Katy showing us a live beetle.


Katy also showed us lots of examples of photographs of damaged caused by Spruce bark beetle, and how to identify ‘galleries’ where they collectively live and breed.  Signs include lots of weeping sap as well as entry holes for the beetle.


She also talked to us about her work around Oak processionary moth – how to identify symptoms and the work that is being done to try to halt the spread of this species, which is a risk to public health in terms of the unpleasant rash and breathing issues that touching or inhaling the caterpillar hairs.


April and Katy will both be sharing distribution maps of pests and diseases in Scotland with the Observatree volunteers, as well as areas that are currently disease free and are being given priority protection, e.g. in terms of timber transport.


April and Katy will share distribution maps with Observatree volunteers


All in all it was a fascinating, inspiring and motivating day.  Thanks team Observatree for inviting me along.  In 2020 we will be running some joint monitoring visits for Observatree volunteers to compare notes in terms of ID and reporting.  Meaghan Henry (lead Observatree volunteer for Scotland) and I will be in touch soon with suggested dates.


Matilda Scharsach

Scotland Volunteering Development Officer










1 Comment
  • Kay Crawford

    Must have been a very interesting day out.

    December 10, 2019 at 4:36 pm

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