Yesterday at work I informed a customer that by not taking a plastic bag they were doubly aiding the natural environment as in addition to reducing plastic waste they were contributing to the enhancement of the great British outdoors through the company’s policy of donating a penny for every bag Not used to the Woodland Trust. Does that mean one more ash tree gets saved then? Quipped the customer in question. Let’s hope so, I replied, though it occurred to me as I said it that even though I am familiar with the species as being one of the more common trees of British woodland I wasn’t entirely sure what one looked like. I love trees, but will shamelessly own up to being woefully under-informed when it comes to matters of dendrology.
It came as no surprise when I read in an article earlier that lack of specialist expertise was cited as one of the main factors in the Ash Death Problem. Apparently tree pathogens and disease in arboriculture are less and less frequently featuring on syllabuses of biology degrees across the nation. I struggle to think if I learnt anything about trees at university aside from the fact that a dead tree supports a far greater spectrum of biodiversity than a living specimen, what with the habitat and food matter it provides for a host of invertebrates, fungi and micro-organisms within the decaying wood matter, in addition to the structural construct that the mass of a fallen or standing dead tree can still provide for many birds, small mammals and epiphytic or climbing plant life. So if someone who purportedly has an environmental degree can’t even tell a healthy ash tree from another species, let alone the less ecologically minded members of the masses and classes, what hope is there?
There are over sixty species of ash tree belonging to the genus Fraxinus, a group of trees with pinnate leaves (which means leaves coming off either side of a central stem) that belongs to the same family as olive. Native to Britain, and featuring in the media spotlight, is the European ash Fraxinus excelsior. The word ash stems from Old English asce (also the runic Æ). Both this word and the Latin Fraxinus mean ‘spear’: the wood was often used to make spears (as well as baskets) because of its springiness and straight grain. In Norse mythology the tree Yggdrasil, on which the nine worlds were supported and whose roots extended into the well of the heavens, was purportedly an ash. Given the majestic stature, form and spread of a mature ash tree (over 40m, living for over 400 years) you can see how this could be plausible from a mythopoetic point of view. Although Yggdrasil supported a range of fantastic beasts such as a dragon, an unnamed eagle, and four stags, the size and structure of the European Ash means in reality is supports an even more impressive range of life forms – including around 100 species of insect and more than a quarter of Britian’s lichen species – both within the tree itself and in the surrounding area as its open branches allow enough light to penetrate through to ground level for a diverse undergrowth to exist at the tree’s feet.
In Britain it’s not just large singular ash trees or woodland stands of the species that are so important, ash is a valuable component of the hedgerow network either as a mature tree standing along a boundary, or smaller specimens interwoven within the hedge framework, with their supple branches working well for traditionally laid hedges. Even though I think I don’t know what an ash tree looks like, the chances are I see them on a daily basis. This is why the ash dieback problem is such a major issue: ash trees form such a large percentage of our native woodland that if the dieback goes unchecked we could lose 80 million trees and the hedgerow network could spread the disease quickly between isolated ash woodlands.
The problem is caused by fungus Chalara fraxinea, first seen to be infecting ash trees in Poland ten years ago, though not scientifically ‘described’ until 2006 as the asexual form of Hymenoscyphus albidus (which is harmless, it’s just the Chalara form that’s the problem). It grows in summer on the petioles – the ‘stemlet’ that attaches the leaf to the main stem – in the leaf litter and spreads by ascospores in the wind, which is why it is so hard to contain infection. The fungus infects the tree through the stem, causing a diamond-shaped purple or black lesion. The infection then travels through the xylem, or water-bearing cells, and eventually kills the tree by starving it of water. Affected trees can be identified by the dead, shrivelled and blackened leaves still hanging on the branches. Ash trees shed their leaves in autumn, but the leaves don’t die whilst still on the branches, they start to turn and are then shed deliberately by the tree forming a little seal like a scab between the petiole and branch to prevent water and nutrients reaching the leaf so the leaves drop off and then die. (I’m starting to wonder as to the species of a young tree covered in leaf corpses of non-autumnal fatality I spotted near here.)
From Poland the disease spread across eastern and northern Europe wiping out huge numbers of trees. As a group of islands the UK was thought to be the last remaining haven for ash trees as it was assumed the ascospores would not be carried across the sea. Studies in Denmark, where over 95 percent of the ash tree population has been wiped out by the disease, have found that a small number of trees appear to be resistant to Chalara infection and scientists were hoping that if the UK were to remain clear of ash dieback it would be able to provide a suitable population in which to study the potential for genetic resistance to the fungus. However, since the first infection was found in a Buckinghamshire nursery earlier this year introduced by saplings imported from the Netherlands, surveys have found ash dieback to be worryingly widespread here in the wild. It has become clear that spores must have reached us on the wind in about 2010, as the extent of dieback in many specimens indicates over a year of infection, so even if the government had acted sooner, the disease would have already been here.
So if the disease reached the UK under its own devices, why is the government under so much pressure for its slow reaction, and why has there been so much media interest in the case? To some extent the media interest has fuelled its own fire, and the fact that there is potential for governmental blame must have intensified the focus on the subject. Woodlands are seen as a national treasure, a symbol of Britishness: when proposals were drawn up last year for the privatisation of the nation’s forests it became clear just how strongly the English felt about their woodlands, despite the surprising fact that Britain is one of the least wooded countries is Europe. Although beyond memory for my generation, the devastation wreaked throughout the UK’s woodlands by Dutch elm disease during the 1960s and 70s (caused by a beetle from Holland) must be at the forefront of the minds of government ministers and the heads of organisations such as the Woodland Trust, the RSPB and Natural England. What has to be borne in mind is that the UK’s woodlands are much more severely threatened now than they were forty years ago; ash dieback could be a potentially much larger disaster than Dutch elm, and not least because the ash population is so much larger than the elm population was initially.
Wednesday saw an emergency conference regarding the problem. Friday saw DEFRA publish its official line on action for ash disease. Due to the extent of Chalara spread in the wild it has been decided that eradication is not possible, although this does not necessarily mean that the disease will completely wipe out the British ash population. Mature trees found to be infected are not recommended to be cut down, partly because they take much longer to die and until they do so will support such a number of species, they will provide good case studies for scientific research into species resistance, and even when they do die – as I correctly surmised from my somewhat patchy ecological education – they will continue to provide a habitat and framework for woodland wildlife.
If the worst were to happen and 95 percent of the estimated 80 million ash trees in Britain dies it would ultimately change not only the way the British woodlands look, but the entire biodiversity network within them. What has to be taken into account is that it would not happen overnight: mature trees take a long time to be killed by the fungus, so although change would be sudden compared to the usual woodland evolutional timeframe, it would be at a pace that would allow surrounding species and wildlife to adapt, perhaps more quickly than would normally happen. Certainly there would be species that would benefit from fewer ash trees. Woodlands with higher densities of Fraxinus excelsior would become lighter and more open, allowing lower canopy species more space and different possibilities for woodland floor dwellers. Healthy British woodlands are made up of a mixture of broadleaved tree species, a deliberate step by foresters and land managers to help in situations like this so that if one tree species were to be wiped out by disease one doesn’t lose the entire wood. Ecologically woodlands, and all habitats, function in balance, so that when one niche becomes vacant something else fills in the gap. What could be seen in the future if the ash population is devastated is that another tree species becomes more successful. The main problem with this is the timescale: broadleaved woodlands take more than one lifetime to come into maturity, so there would be no quick answer as to how the balance might redress itself.
It also has to be considered that a very small number of ash trees are resistant to Chalara. Natural selection would see these variants thrive, and with funding in the right places these strains could be nurtured to provide saplings to help, if not regenerate, then at least recuperate, the ash population. What is perhaps the most enlightening thing to come out of the ash crisis is the extent of concern shown by people about the state of the woodlands, compared to the time and money being apportioned by the government for use in this area. What must be kept sight of, and hopefully will be in light of the attention given to Britain’s woodlands over ash dieback, is that this is just one problem for a well-loved aspect of the British countryside that is threatened in a number of ways yet is often too far down the list of priorities.
And I’m no exception: I realise now it’s taken an event such as this for me to even take any notice of the Third Most Common British Tree. Must try harder? I’m sure we could all be better informed about many things that matter. What I do know is that to learn more about the things you say you care about means you’re in a better position to actually care for them, whether that means voting for the right people come election time, or knowing when to wash your boots after a walk and check out exactly what tree species that was that you saw dead on its feet in the woods down the road.
Links to relevant articles are highlighted throughout the article.
There is a huge amount of information available elsewhere but for the basics, The Forestry Commission is a fairly informative starting point.