The latest Forestry Commission assessment of the spread of ash dieback (caused by the fungus Hymenoscyphus fraxineus, previously called Chalara fraxinea) shows a consolidation of the wider environment outbreaks in the North East and North West, with the “front” continuing to move towards the West across the entire country – perhaps more slowly than some earlier predictions. There are lots of possible explanations for this, not least that the disease hasn’t had much press coverage lately – people simply aren’t looking for it.
Many ash trees across the country, particularly in the north and west, were very late leafing and had low flowering rates this year, with unusually light canopies and poor coppice growth. This prompted discussions over whether ash dieback was responsible, despite the absence of the classical symptoms of dark lesions and hanging, dead leaves.
However, looking back to last year, conditions allowed many trees to produce an abundance of seeds, a hugely energy intensive effort that might otherwise have gone into leaf production. So it could just be that many of our ash trees took a bit of a breather this year. The trees with the most threadbare crowns did seem – anecdotally at least – to be those that were carrying most seed from last year.
Life is the delicate balance between survival and reproduction. Ash dieback is just one of the many threats that ash trees face and they have evolved to react accordingly – when conditions allow they will invest heavily in seed production, at other times they hunker down and try to weather the storm. It’s a life history strategy that has served the species well and no doubt will continue to do so. And the countless millions of new genetic combinations represented in those bumper seeding years are surely the best way to find the right one(s) to resist ash dieback.
Tracking the spread of ash dieback is vital to our understanding. With the onset of autumn, the most reliable symptoms to look for are those bark lesions; easier to spot in younger trees and especially so as the leaves fall away. Our network of volunteers and supporters can play a vital role in tracking the spread of the disease, by reporting any symptomatic trees using the Forestry Commission’s TreeAlert phone app.
Nick Atkinson, Senior Advisor