Mourn the passing of the ash tree, but for conservationists, there is a silver lining

The deadly Chalara fungus threatens ash trees, but the dead wood will provide a cornucopia of invertebrates for birds to feed on

Dr Malcolm Smith
Monday 19 November 2012 19:35
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A lesion on an infected Ash tree in Pound Farm Woodland on November 8, 2012 near Ipswich, United Kingdom. The Ash Dieback outbreak has the potential to devastate the UK's population of 80 million ash trees. The first confirmed case in the UK was in March 2012, and since then, dieback has been confirmed at a further 82 sites, with woodlands in Norfolk, Suffolk, Kent and Essex among the worst affected and has now spread to Scotland. Dieback is caused by a fungus Chalara Fraxinea and was first recorded in Eastern Europe in 1992, spreading over two decades to infect most of the continent.
A lesion on an infected Ash tree in Pound Farm Woodland on November 8, 2012 near Ipswich, United Kingdom. The Ash Dieback outbreak has the potential to devastate the UK's population of 80 million ash trees. The first confirmed case in the UK was in March 2012, and since then, dieback has been confirmed at a further 82 sites, with woodlands in Norfolk, Suffolk, Kent and Essex among the worst affected and has now spread to Scotland. Dieback is caused by a fungus Chalara Fraxinea and was first recorded in Eastern Europe in 1992, spreading over two decades to infect most of the continent.

Jimi Hendrix was right. “Once you’re dead, you’re made for life,” the rock god commented at some point in his short existence. Unlikely though it is that he was referring to dying trees, his aphorism goes to the very heart of the cyclical process of life, death, decomposition and new life that characterises all plants and animals.

We will rightly mourn the demise of ash trees from our woods, copses and country lanes if most of them succumb to deadly Chalara fungus. But the dead wood they will provide will be an enormous boost for Britain’s biodiversity.

Dead wood is the richest habitat in a healthy forest. It supports a huge variety of wood-boring invertebrates – around 1,800 species – a veritable army of little rotters that slowly eat it up: beetles, hornets, weevils, wasp-mimicking flies, spiders and pseudoscorpions, plus a battalion of fungi whose thread-like filaments penetrate deep inside to slowly decompose it, returning its nutrients to the forest soil.

A forest with plenty of dead timber provides a cornucopia of invertebrates for birds such as nuthatches, warblers and woodpeckers to feast on. And large dead trees, because rot holes more easily develop in them, are good places for hole-breeding species like bats, jackdaws and tawny owls.

Britain-wide, we have interrupted this natural cycle. In woods managed for timber, trees are felled before they mature, denying them a chance to senesce and sport large dead limbs. In most other forests, fallen branches brought down by gales are carted away for public safety reasons, to be used for firewood, or simply to keep the place “tidy”.

On a woodland walk, we have become accustomed to a sanitised version of a natural forest. We no longer expect to see standing dead trees. So the borers have precious little sustenance and a fifth of them are now rare or endangered. But natural forests – those left to their own devices – are full of dead timber amongst the living trees, rich in rotting invertebrates and a plethora of fungi.

A survey in the late 1990s led by Dr Keith Kirby, a leading woodland expert, found that, out of 37 English broadleaved woods, three quarters had either no standing dead trees or less than two per hectare. A natural forest (Britain has none) might have more than 50. Belatedly, many foresters and woodland owners have woken up to the need to retain some dead wood. Others haven’t. Our woods still desperately need more of it.

If swathes of ash trees start dying Britain-wide, the policy of fell and burn to stop the spread of the fungus will serve no further purpose. Dead trees mustn’t be squandered. Provided they pose no safety hazard, let’s leave them where they are to decay and fall naturally, and to attract the army of little rotters waiting to do their vital work and enrich our woodland biodiversity.

Dr Malcolm Smith was chief scientist at The Countryside Council for Wales,1996-2004, and a board member of The Environment Agency, 2004-2010

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