Tuesday, October 30, 2012

More on ash die back disease

My mail box continues to be crowded with injunctions to help stop the spread of ash die back disease, Chalara fraxinea.  As someone who has done many years of study on our native trees and has the greatest possible affection for them I do not want to be seen as not caring about the ash.

However, I do think we have to be realistic.  It seems to me there is little chance of stopping a fungal disease that is spread by spores and is widespread all over Europe right up to the Channel coast from advancing into the UK (as the Forestry Commission suggest it already may have done) by perfectly natural means as well as on imported plants.

Prompted by this recent emergency I was particularly noticing ash trees on my way into Hastings this morning, a journey of about 10 miles.  There must be thousands, many the young trees that appear to be particularly susceptible, in hedgerows, on embankments as well as in the edges of the woodlands that I could see.  It would be very difficult to survey all these trees carefully for die back and, if the disease were found the prospect of the damage to the countryside that would result from unearthing them from hedges etc. is alarming.

Where the A21 enters Hastings there are steep embankments covered in young ashes on either side of a road bridge.  If the disease were to occur here, trying to deal with it (bearing in mind that it might be in the roots as well as in the top hamper) would involve major engineering works and probably significant road closure.

It occurs to me that the disease has probably been identified in plant nurseries and on Forestry Commission and Woodland Trust properties because young trees in these places get much more detailed scrutiny than elsewhere.  Many woods have  thousands of young ashes as well as older ones, often in rarely visited spots and systematic survey and destruction of the infected would involve an impossible amount of people hours and cost.  There will no doubt be extra vigilance in well-visited woods, but there are many places where ashes grow on farmland and other private property where detailed scrutiny is unlikely to take place.  Indeed, one of the characteristic habitats of the ash is on vertical limestone and other cliffs ...

While the present government does not seem to be particularly pro-wildlife, blaming them for outbreaks of ash die back in the wild as a consequence of not preventing imports of the trees sooner than they did seems like blaming the American government for hurricane Sandy.

If ash die back becomes widespread in the UK, as seems likely based on the experience in other European countries, it might be better to look for trees that do not have it rather than those that do.  As I said in yesterday's post, there seem to be some chalara-resistant strains of ash and these will need to be cherished.


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