Warburg Nature Reserve is one of the jewels of the Chiltern Hills. In autumn, its beech, birch and oak trees transform into a dazzling canopy of red, yellow, brown and gold leaves. Budgies and red kites soar above our heads as a surprising variety of fungi, from milkheads to collared kites, scurry across the forest floor of the 100-acre site.
This curtain of multicolored delights hides, however, a dark secret. A walk around the reserve, owned by the Wildlife Trusts, reveals gaps that have recently appeared in the foliage.
White, leafless trunks tower over the paths, all victims of a pernicious blight that is destined to strip our forests and take millions of pounds out of the budgets of wildlife charities – the death of ash.
The disease, caused by the fungus Hymenoscyphus fraxineus, first appeared in the UK a decade ago. At the time, experts warned that the ash die-off would have a serious impact, although some hoped the resilience would spare some trees and leave parts of the forests relatively unaffected. Now, 10 years later, this perspective seems abandoned.
“I think we’ll be lucky if 5% of the country’s ash trees survive this catastrophe,” said Debbie Lewis, head of ecology at Berkshire, Buckinghamshire and Oxfordshire Wildlife Trust (BBOWT), which manages the Warburg reserve.
Debbie Lewis, left, chief ecologist, and Steve Proud, director of land management, at Berks, Bucks & Oxon Wildlife Trust. Photograph: Robin McKie/The Observer
“On its own, the loss of our ash trees is a tragedy, but it’s also having all sorts of knock-on effects. Warburg is a popular reserve visited by thousands of people and this raises costly health and safety issues,” he added.
The key problem for Warburg, and for all the reserves managed by the other 45 Wildlife Trusts in the UK, is that more and more ash trees are dying and their huge decaying trunks are hovering over paths and clearings. Many are in danger of falling and are becoming a threat to visitors and workers.
“These dead trees grow on slopes and near rights of way and represent a danger. So cleaning them up has become a priority,” said Steve Proud, who is BBOWT’s director of land management. “But it’s a complex and expensive business that requires specialist intervention.
“Our trust has already had to spend £400,000 to pay for tree clearing, and we expect to have to pay a further £800,000 over the next few years. That’s a lot of money for a local wildlife trust and means we have much less to spend on wild habitat restoration, which is our primary focus and goal.”
However, making sure we humans are not harmed is not the only difficulty facing Warburg’s reserve. Many of its ash trees are home to bats, such as brown-eared bats and long-eared bats, and as these animals are protected by law, the trees must be carefully checked to make sure they are not nesting there. “Pointing out the tiny markings of a nest at the top of a 40-foot-tall tree isn’t easy, but it has to be done,” Lewis added. “And it all adds to the work we now have to do to deal with the ash die-off.”
This point was supported by Rob Stoneman, director of landscape recovery at the Wildlife Trusts. “The impact of ash die-off will be even greater than that of Dutch elm disease, which has killed millions of trees since it appeared in the 1970s. Our forests, particularly in the north of England , are dominated by ash trees, so they will experience very rapid changes over the next decade.”
The brown long-eared bat depends on ash trees to build its nests. Photograph: blickwinkel/Alamy
The consequences for some smaller trusts could be severe, Proud said. “We are a relatively large trust, but the smaller ones are having to sell their assets and reduce educational sessions to provide money to deal with the death of the ashes.
“We face massive spending over the next three to five years, thanks to the ash die-off, and this will come against a backdrop of reduced income as inflation rates hit our members’ incomes.
“There is a limit to which we can depend on your generosity. So this threatens to become a perfect storm for us.”
The ash die-off is just part of a larger pattern of changes in our forests, Stoneman added. “In continental Europe, we’re seeing an increase in a whole range of diseases, like oak processionary moth disease and pine rust. And that’s probably because trees are being stressed by climate change.
“We’re having hotter, drier summers and wetter winters and that makes trees more susceptible to disease. Climate change is already having really significant effects.”