Thursday, 15 November 2012

Photographing Ash Trees and Remembering Dutch Elm Disease

At this time of year, shortly after dawn, I often walk across the fields towards the woods. The air is sometimes a little misty, the sun is low and the trees still shadowy.  As I follow a well trodden route across the woodland, I can see and feel at once that the trees are shaking off their leaves and the woodland floor has become a carpet of copper and gold.

The woodland I walk through is mainly sweet chestnut and hornbeam, with some oak.  But out in the fields there is ash; both mature trees and some self-sown, young saplings.  Now that ash dieback has begun to spread across Britain and is already in Essex, I have an ominous feeling that these wonderful ash trees could well be destroyed.


Ash Trees
 And we've been in this situation before. I can just remember the appalling loss of the elms from Dutch Elm Disease (DED); one of my earliest memories is the sound and sight of several mature elms being felled in my local churchyard and the giant bonfires to destroy every last trace of their existence.  Ash and elm are two different species, of course, and the development of ash dieback and DED won't be the same, but the impact on the landscape could be.

I've recently seen old photographs of large elm trees about to be felled with photographs of the same location after they've gone (essentially "before" and "after" pictures).  The "after" photographs show huge gaps in the landscape where the elms should be.  I've now decided to photograph mature ash trees in the same way that the elms were photographed, even though it may be years before they disappear (if they do).  I'm not going to rush out and photograph every ash tree I come across,but it does seem a good time to really appreciate these trees and record their place in local landscape history.

DED and its control
As a wide-scale destruction of ash trees is talked about, I recently had a look at the devastation caused by DED in the 1970s (both nationally and locally) to see what happened then.

Here are my discoveries:

Background

- The British elm population is quite diverse but all groupings of elms are susceptible to DED.  Only small pockets of mature elms still exist in Britain today.

- Modern DED was first discovered in northern Europe (Picardy) in 1918.  It was found in Britain (and Essex) in 1927.  An early theory about its origin was that it had been caused by toxic gas in the First World War, but later it was generally believed that it had been imported from Asia.  In fact, there is evidence to suggest that DED has been in Britain for centuries (from tree rings and also from references in documents to the sudden death of elms in an area).

- The strain found in 1927 was eventually considered non-serious, as by 1929 there were signs of recovery in the elm population.  T R Peace, who assessed DED, wrote in a Forestry Commission publication in 1960 that this disease could well continue as a minor nuisance, but unless its nature changed, it would never amount to any great importance.

- In less than a decade after Peace wrote the above, DED in Britain had changed.  In the late 1960s, elm imported from North America was found to contain a more virulent strain of the disease and elms across Britain were quickly infected. It wasn't long before elms were inspected, assessed and destroyed.

- Since the 1960s, the existence of DED has prevented the growth of mature, healthy elm trees.  Elm continues to grow in hedgerows, but if these hedgerows aren't managed properly i.e. they are left to grow into trees, then they will succumb to the disease.


Elm Hedge

The Nature of the Disease

- DED is caused by a fungi in the genus Ophistoma and is transmitted from dead or dying elms to healthy trees by a species of elm bark beetle.  The female beetle lays eggs under the bark; when the eggs hatch the emerging beetles rub against the sticky spores of the fungus and then, when they come to breed, they fly to the crowns of healthy trees.

- the symptoms of the disease are yellowing or browning on the foliage of trees, dying twigs (that bend over and resemble a shepherd's crook), brown streaks on the bark and an absence of healthy buds.

Control of DED

- A programme of sanitation felling was implemented and sanitation measures "on the table" in 1970s were as follows:

1. Root severance - severing the roots between a tree and its neighbour.  This could be done by mechanical measures (digging out a trench and digging out the roots) or by using a chemical to kill the roots.
2. Fungicidal Injection - this was a new treatment in the 1970s and involved injecting a fungicide into the tree.
3. Spraying Insecticide - this was to be done by "mist spraying" and helicopters could be used for this.

The idea of insecticides and chemicals makes me shudder, but in the 1970s the damage to the environment by these measures was seemingly not fully considered or appreciated.  In the end, spraying with insecticide was to be abandoned because of ineffectiveness and environmental damage while injecting with fungicide was to be abandoned because it was considered too costly.

Some of the most recent attempts at combatting DED are being made in the breeding of disease resistant trees.  A nursery promoting disease resistant trees is to be found in Essex.

The Legacy of DED

The British countryside has been changed completely by the loss of the elms.  In Essex, records made by the local council detail where the elms were felled.  In the coastal areas of Tendring, Dengie and Thurrock elms dominated the local hedgerows and so their destruction here hugely damaged the local landscape and its wildlife. 




2 comments:

  1. Dutch elm disease brought much distraught among those that lived in the area, it was almost as bad as the now emerald ash borer situation is.

    -Samudaworth Tree Service

    ReplyDelete
    Replies
    1. Dutch Elm Disease was devastating here; there are very few places that still have mature elms.

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