Why ash matters in our woods and hedgerows

Ash is one of the quiet architects of the British countryside. It is the tree that fills our hedgerows as seedling keys, lines the lanes where you walk, and rears up as grey-barked standards in old coppice and wood pasture. Its timber has been cut for tool handles, gate hangers, waggon shafts and hurdles for centuries, and pollarded ash in ancient wood-pasture can be four or five hundred years old. It is, in short, part of our countryside heritage as much as any hedgebank or stone stile.

Which is why ash dieback matters so much. The disease is caused by a fungus, Hymenoscyphus fraxineus, which first reached the wider British countryside in 2012. Wind-blown spores land on leaves, the fungus grows down into the shoots and branches, and over years the crown thins and the tree dies. Surveys suggest we could lose the great majority of our ash in the coming decades, with the heaviest losses in the east and south-east so far. There is no cure, but there is plenty we can do: recognise the signs, report what we find, and protect the trees that are still healthy.

Recognising the signs, bark to crown

Start by standing back and looking at the whole tree, then move in close. Ash leaflets are typically in pairs on a stem with a single leaflet at the end, so a tree with no leaves may still be identifiable by its distinctive black buds and opposite branching.

• Blackened, shrivelled leaves clinging on. In late summer and winter, dead leaves hanging in tufts on the shoots are the most reliable field sign, especially low down on hedgerow ash.
• Diamond-shaped lesions. Look where the branch meets the trunk: sunken, olive-brown to purplish patches, often shaped like a long diamond, spreading more quickly along the branch than around it.
• Crown dieback from the top down. The tips die first, giving the tree a thin, spiky, "ghost" silhouette by mid to late summer.
• Epicormic growth. Bushy clusters of shoots sprouting from the trunk and lower branches are a stressed tree's attempt to replace lost canopy.
• Basal lesions. Dark, sunken patches near the root flare, sometimes with a narrow "neck" of bark dying around the base.

Timing your walk — and ruling out lookalikes

The best window for checking ash is late June to September. Leaf emergence in ash is late anyway, often mid-May, so don't panic in April. In winter, hunt for those blackened leaves still attached to the shoots; on hedge-laid ash and young standards they are often the first clue.

Not every sickly ash has dieback. Ash bud moth, drought stress, ash rust with its orange pustules, squirrel stripping, flail damage on roadside hedges and waterlogged ground can all mimic parts of the picture. Dieback is usually a combination: crown thinning plus lesions plus retained dead leaves. If in doubt, record it and let a tree health specialist judge.

Reporting a suspected case

Suspected cases are worth reporting: records help track spread, inform safety work and highlight trees that may be tolerant. Take three photographs if you can — the whole tree, the affected crown, and a close-up of a lesion or hanging leaves. Note the grid reference from a map, the date, and whether the tree stands in a hedge, a wood, a park or beside a road.

Send the record to the national tree health reporting service, or to your local council's tree officer for street, park and highway trees. If you manage the wood yourself, bring in a qualified arboriculturist before doing any work: dying ash is notoriously brittle, and limbs can drop without warning. Keep visitors away from suspect trees beside paths and car parks, and remember that standing dead ash still has real value for beetles, fungi and woodpeckers where it is safe to leave it.

Biosecurity: small habits that protect healthy ash

Spores travel on wind and in leaf litter, but people move them too, on boots, tyres, tools and timber. A few practical steps make a real difference.

• Clean your boots before and after a wood visit: brush off mud and leaf litter, then disinfect with a 70 per cent alcohol spray or a proprietary woodland disinfectant.
• Stay on paths in ancient woodland, especially in spring and after rain, and keep dogs to the path too.
• Never move ash material — logs, firewood, saplings, leaf litter or woodchip — between sites or from a suspect tree.
• Avoid pruning ash between June and August if you can; fresh cuts are open doors. Winter work is safer, with clean, disinfected tools.
• Provide a biosecurity station — brush, spray, a bin for muddy debris and a simple sign — at the entrance to any site you manage.

Looking for survivors and reading the heritage around you

A small proportion of ash appear to tolerate the fungus and stay healthy in a dying stand. If you find one, note it precisely: these trees matter enormously, and seed collections and archive plantings are being built around them. Fence veteran and ancient ash from livestock where you can, and resist the urge to clear a whole hedgerow at the first sign of trouble.

And while you are out there, read the landscape. Ash was the classic standard in a laid hedge, cut on a twelve to fifteen year rotation for poles, and old stools and pollard scars are still visible on many banks. Ash before oak, we're in for a soak — the old rhyme still holds. Recording what you see, carefully and often, is one of the most useful things an ordinary walker can do for the trees that are left.