Disease threatens to change landscape

Ash die-back disease presents a clear and present danger to woodland. Sebastian Oake talks to a ranger on the future for our woods

National Trust ranger Peter Katic strides with purpose, and yet a hint of reluctance, towards a small wood on the Dales fellside. I am with him on the trust’s huge Upper Wharfedale estate at the heart of the Yorkshire Dales National Park, a place with great natural beauty that was previously thought untouchable. But a new threat is now on the horizon. Could ash die-back disease change the whole face of this landscape?

As we walk high above the still young River Wharfe as it makes its way down Langstrothdale, it hits me just how numerous ash trees are here. Almost everywhere you look you can see them, from gnarled old specimens living out their days quietly, to hopeful young saplings, shooting up wherever they are out of reach of the ever-nibbling sheep that claim these limestone slopes as their own.

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Peter is surveying ash trees for signs of Chalara or ash die-back disease. He stops at a moss-covered giant that he estimates could be up to 175 years old. The leaves have fallen but he’s studying the twigs intently. “There’s been good growth this year and these twigs are smooth and healthy,” he says. “There are some lesions but there’s no sign of blackening, so I don’t think they’re the type we’re looking out for.”

Lesions around dead side shoots or leaf scars are one of the tell-tale signs of Chalara, along with necrosis of leaf tips, spreading down the veins into the main stalk. The disease causes leaf loss and crown die-back and leads to death in all but the largest of trees. There is no cure.

The disease was first found in Britain last February, when a nursery in Buckinghamshire received a consignment of infected stock from the Netherlands. More recently the disease has been identified in the wider environment, established woods where it probably arrived via spores carried on the wind. It’s the latest move in the disease’s steady march across Europe. In 1992 it was found in Poland and Lithuania, by 2003 it had taken hold in Denmark where it has infected around 90 per cent of ash trees, in 2007 it was in France, in 2010 the Netherlands and now, it seems, it is our turn.

Peter Katic is pleased not to have found anything wrong with the mossy old tree before us but his main fear lies ahead. We are heading to Strans Gill Plantation, a place that holds special significance for him. “Sorting out this plantation was one of my very first jobs for the National Trust here 20 years ago,” he says. We open the gate into the two or three acre enclosure and enter a delightful mixed stand of beech, sycamore, Scot’s pine, maple and, it hardly needs to be said, ash. “I built the walls back up, cleared fallen timber and made clearings to allow the light in,” he explains. “I also planted some new ash but there was no need – wherever there was light, ash shoots sprang up naturally.”

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I look around and it’s true. In places the under-storey is a veritable thicket of young ash. “I would be really sorry to see all these ash trees disappear. I have watched them grow up for two decades.”

It’s soon apparent that some of the planted and naturally regenerated ash is still in leaf. I am dismayed to see that, even to my untrained eye, there seems to be definite die-back of the pinnate leaves. Peter’s face goes expressionless as he examines his Forestry Commission disease guide and compares the photos there with what faces him now. I’m thinking that the game is up already but Peter breaks the ice. “There are no lesions, no sign at all really that this is anything different to healthy leaves just dying back naturally in the autumn.”

It’s good to hear. I ask him what he would have done if the check had been positive. “Take a picture, record the location as accurately as possible and leave. Once you’ve found the disease in a wood, there’s no point in looking further.”

And the outlook does seem to be worsening. Latest figures show ash die-back has been identified at more than ten places in wider Yorkshire. It is not yet present in the Yorkshire Dales but for how long will things stay that way?

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In Upper Wharfedale it’s obvious, painfully obvious, that a lot of the woodland has a high proportion of ash. Not only that but the National Trust has also planted thousands of new ash trees to create new woods in gills. Just what would happen if the disease were to take off here?

“I am quite a positive person,” says Peter Katic. “I’m trying to persuade myself we might not see the drastic effect they are telling us we can expect. My hope is that not all ash will die back. Some will be naturally resistant – because that’s the way of things – and hopefully they will produce seed that might spur regrowth. Ash will regenerate amazingly given the right conditions. But I admit, this is all speculation at the moment.”

In the shorter term, if the disease were to strike, it could lead to a large number of standing dead and dying trees. “A certain amount of standing dead wood is beneficial for wildlife,” says Peter, but we don’t want too much. It wouldn’t look nice.”

The tree of the Dales

Anyone who has visited Wharfedale, Langstrothdale, Malhamdale or any of the others will know that the Yorkshire Dales means ash, and ash means the Yorkshire Dales. If the National Park had not chosen a ram’s head for its symbol, then it could have legitimately picked an ash leaf instead.

Peter Katic puts it all into perspective: “Ash is the large tree of the Dales. One of the good things about Upper Wharfedale is that it does have a lot of trees.”