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Threats to British TreesFor Tony Kirkham it was yet another grim find. One of the towering oaks, a tree that had dominated its patch of Kew Gardens for 250 years, was dying.
At 90ft high and still in its prime, the tree had seemed ready for another 250 years, but suddenly it began losing its leaves, bark began peeling away and beetles began digging into its wood. Soon branches started to fall off, turning it from a visitor attraction into a potential hazard.
“We’ll probably have to cut it down next year,” said Kirkham, head of the Kew arboretum, last week. “It’s really sad to see it go, especially when you think of all it survived. It was planted around the time George II was on the throne.”
Kirkham’s dying oak is, however, just one of many. All over Britain native trees are under attack from exotic microbes, pests and environmental stresses that were never expected to get a hold in Britain.
Oak decline, the syndrome affecting the Kew tree, is one of the more mysterious ones but there are plenty more, ranging from fungal infections such as bleeding canker and sudden oak death, to the weirdly named oak processionary moth and the horse chestnut leaf miner.
All of them originate far away from Britain — and only began spreading here recently. Between them they could wipe out millions of Britain’s best-loved native trees.
The reasons for their sudden arrival and spread are complex but one single factor stands out: climate change is demolishing the barriers that once protected us from such diseases. What’s more, say experts, as temperatures continue to rise they are going to bring about even greater changes. Faced with frequent droughts and wetter winters, as well as new pests and diseases, many of the species we know and love will disappear. Beech, yew, even the mighty oak are all vulnerable.
So what will the countryside of the future look like? AT Croft Castle in Herefordshire some of those impacts are already evident in the form of 20 dead trees that stand among a mile-long avenue of ancient sweet chestnut trees which has dominated the estate for hundreds of years.
Legend has it that the trees grew from seeds recovered from the wreckage of the Spanish Armada in 1588. They had thrived in the cool, wet climate — until now.
The deaths were from ink disease, a root disorder caused by a fungus that creeps through the soil and which was rarely seen in Britain until the 1990s.
The National Trust, which owns the estate, is fighting to save the rest of the avenue. Ray Hawes, the trust’s head of forestry, said: “It’s so sad when you lose such trees, because you’ve lost hundreds of years of history and beauty along with it.”
The story is similar at the Queen’s Enclosure, near Portsmouth, where Henry VIII and his successors once planted thousands of giant oaks.
They realised that equipping the Royal Navy with magnificent oaken ships like the Mary Rose was going to destroy England’s woodlands and so embarked on a mass planting programme.
Henry VIII thought long-term. His trees have only just matured and are ready for turning into warships — or they would have been were it not for a sudden outbreak of exotic fungal infections that now threaten the whole plantation.
“Those trees are showing the classic signs of stress and the risk is that many of them will succumb,” said Kirkham.
Britain’s forests and woodlands have, of course, always been subject to great changes.
After the last ice age ended, the whole of the British Isles would have been wooded, with oak, beech and ash dominating the lowlands, while tough conifers, mainly Scots pine, covered the northern uplands.
Then humans arrived — and began cutting down millions of trees, at first for fuel, but increasingly as a raw material for construction, weapons and other purposes.
Agriculture played a huge part too. Clearing land was essential to produce enough food for a burgeoning population.
By the 15th century Britain was getting short of wood and by Nelson’s time the shortages were growing acute. In 1801 England even went to war with Denmark after it threatened to cut off the timber exports on which the Royal Navy relied for its ships. The Battle of Copenhagen became one of Nelson’s most famous victories.
The nadir was reached during the first world war, when Britain plundered its remaining woodlands, leaving just 6% of the country with tree cover. Since then the coverage has crept back up but even now it still only stands at 6.9m acres or about 12% of the land area, far less than most other European countries.
Some superb woodlands remain. The New Forest, Forest of Dean, Glen Affric and Thetford Forest are among the most outstanding.
Take a close look, however, and all of them are facing new threats that could transform them faster than anything that went before.
One such threat is red-band needle blight, a fungal disease once found only in the southern hemisphere. The disease attacks more than a dozen conifer species but has proved particularly devastating for Corsican pine, a major commercial species.
In Thetford, which is dominated by the species, and other woodlands, tens of thousands of dead trees now stand in what were once flourishing plantations. The fear is that it will now spread to Britain’s native Scots pine.
Other diseases such as sudden oak death and bleeding canker are provoking even more alarm. Both are types of phytophthora, related to the fungus that wiped out the Irish potato crop in the mid-19th century.
However, rather than attacking vegetables, they target some of Britain’s best-loved tree species, such as beech, yew and fir.
A Forestry Commission study recently found that 49% of Britain’s 2m horse chestnuts were already infected with bleeding canker.
Last week Jane Kennedy, the environment minister, announced a £25m eradication programme, targeting the rhododendron bushes that harbour the infection. She also confirmed that further “hotspots of disease” had been found in the New Forest, the southwest of England and Cannock Chase in Staffordshire.
Such a rapid spread is extraordinary given that sudden oak death only arrived in Britain in 2002. It also occurs in the western USA but studies suggest it originated in another country, as yet unknown.
There are, however, many more threats. One of them is the oak processionary moth, so called because its caterpillars tend to follow one another in a line as they wend their way around infected trees.
The moth was a southern European species until 2006 when it popped up in west London, from where it has since progressed to Kew and many surrounding gardens. Its larvae chew at leaves, leaving trees vulnerable to infection. Worse, they have toxic hairs that can be carried by the wind and cause allergic reactions in humans.
Then there’s the leaf miner, a bug only discovered in the late 1970s in Macedonia but which has since spread across Europe to Britain, reaching Wimbledon in south London in 2002. From there it has moved northwards across England at about 40 miles a year, targeting horse chestnut trees and chewing through their leaves. JUST how much damage can such diseases do?
Trees may look tough and resilient but history shows otherwise. Dutch elm disease is perhaps the most horrifying example. When a new strain of the disease arrived in Britain four decades ago it took just a few years to kill 25m of the country’s 30m elm trees.
Keith Kirby, woodland conservation officer for Natural England, the government wildlife body, predicts that southern England’s “treescape” will change sharply in the next few decades. “Climate change puts Britain into the range of many new pests and diseases found in Europe and elsewhere while also creating stresses of its own through creating more climatic extremes,” he said.
Britain’s woodlands are already showing signs of what this could mean. Several years ago the Forestry Commission, which manages about 1.98m acres of woodlands, found that 4,900 acres of 50-to 60-year-old Norway spruce plantations in Rockingham Forest, Northamptonshire, were declining in health.
Scientists linked it with winter flooding and spring droughts in the previous few years — and said the impact was so bad they should be cut down.
At Rockingham the forest was replanted with native species chosen for resilience. This was a positive outcome, but in the long term the answers are not so simple.
Hugh Evans, biosecurity adviser to the Forestry Commission, said more invasive pests would arrive as temperatures rose. “Rising temperatures will allow more of these creatures to breed here just as trees are suffering increasing stress from climatic extremes,” he said.
Monique Simmonds, professor of biological interactions at Kew, believes that visiting Britain’s woodlands will become a very different “sensory experience” as climate change takes hold.
She said: “The dominant trees will change and so will the look and feel of forests. We are likely to lose the phenomenon of autumn colours, for example, because our native trees need cold before they turn yellow and orange.
“The same goes for smell. The piney or earthy smell of our cool wet woodlands will vanish and instead we’ll have the smell of Mediterranean woodlands, dominated by herbs.”
Some view such changes with regret but others also see opportunities. A few farmers are, for example, already embracing Mediterranean agriculture. One of them recently created Britain’s first olive grove with 120 trees planted along the banks of the River Otter, near Honiton in Devon.
“We have to be ready for change and learn to accept it,” said Richard Smithers, conservation officer with the Woodland Trust, which oversees more than 1,000 woodlands totalling more than 50,000 acres.
“Conservation has traditionally been about preserving or recreating the past but now we need to find sustainable solutions and that means embracing change. After all, the species that are invading Britain from the south need protecting too.”
Courtesy of Times Online
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