Barrell On...The inherent dangers of monocultures

An estimated 80 million of our native trees are ash and they are beginning to die from a fungal disease called Chalara fraxinea.

Already rampant across the continent, it has decimated up to 90 per cent of Denmark’s ash population and it has now been found on mature ash in the UK. To set this into context, Dutch elm disease wiped out most of our 25 million trees, so this disease has a potential impact three times greater than that.

The threat has been known about for years yet the Government failed to ban the import of ash saplings, identified as a primary vector of the disease. Of course, the politicians will have plenty of excuses, dodging the reality of yet another misjudgement in the catalogue of incompetence tainting its approach to the environment. Whereas U-turns are possible with hair-brained schemes like systematically exterminating badgers and selling off our forests, there can be no such reprieve for the trees. It is too late, the damage is done and the opportunity for prevention has been missed.

If it is any consolation, we are not alone in grappling with alien pests and diseases. I have just returned from Canada, where they are bracing themselves for a similar onslaught. This time the menace is from an exotic beetle, the emerald ash borer, which is wiping out ash populations across the USA, with the same prospect for Canada. The inability of governments to react quickly and increasing international trade are global characteristics that are likely to prevail, so can we decrease our vulnerability to these modern threats?

Better border controls will stall the spread and buy time to prepare, but that is not a sustainable solution. Monocultures are high-risk and an effective way to improve resilience is to increase species diversity.

Planting four trees of different species rather than four of the same sounds simple, but it will significantly improve future options. The challenge is getting landscape architects, tree officers, planners and urban designers to buck the monoculture trend, realise the peril and make the small changes needed to deliver a big difference.

Jeremy Barrell is managing director of Barrell Tree Consultancy

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