Destroyed by devastating winds in 1987, the South's forests are taking root again thanks to dedicated arborists

On the night of 16 October 1987, Mike Calnan slept peacefully as the Great Storm ravaged Britain. He didn't switch on the radio as he travelled to work at the National Trust's Cirencester offices. It was only when his phone started ringing off the hook that he realised something very serious had occurred.

Calnan is now the NT's head of parks and gardens. He documented the damage caused by this once-in-300-years storm from a helicopter, compiling aerial photographs of the worst-hit properties in the South-east. It was a sobering sight. "At open-space properties like Slindon, near Arundel in Hampshire, great chunks of woodland had been flattened. Petworth in West Sussex was also very badly hit; we went in low around the pleasure grounds, and where there was once woodland laid out by Capability Brown in the 18th century, there were root plates as tall as houses where the trees had keeled over. They were in full leaf, like sails presented to the wind, and they went down like ninepins."

Worse was to come. "At Emmetts Garden in Sevenoaks, we were dumbstruck. We hovered at a few hundred feet, looking at the scale of the devastation. It was staggering. We saw 200 acres at nearby Toys Hill flattened as if someone had driven a bulldozer over it."

It's 20 years since the nation woke up to the aftermath of the Great Storm. In the South-east, where the greatest damage occurred, winds of 70 knots and more were recorded for four consecutive hours. The strongest gust over the UK was 100 knots, recorded on the Sussex coast. An estimated 15 million trees were lost. Hundreds of thousands of homes were without power for days, wreckage blocked roads and railways. The National Trust's estates that lay in the path of the storm were particularly badly hit. Acres of ancient trees and valuable specimens were destroyed, and some of the estates were changed for ever. Responding to the disaster was a challenge for estate managers and staff that still continues two decades on.

Calnan says that the teams going into the estates the next morning were disorientated. Landmark trees and woodland had been lost, and they couldn't work out where they were. "People were in shock. Some had seen their life's work destroyed in four hours. Some were in tears. You get emotionally involved with a garden. It was a wholesale bereavement; wonderful old trees that had been there hundreds of years had been knocked out."

At Chartwell in Kent and Nymans in West Sussex, important specimen trees were destroyed. Sheffield Park in Sussex lost 50 per cent of its trees and shrubs. Plants such as bluebells that had been thriving in the dappled shade provided by overhead branches were suddenly exposed to wind and direct sun. And trees that were still upright had been stressed or damaged by the fall of their neighbours. Whole microclimates were radically altered.

Gardeners, tree surgeons and foresters were drafted in from all over the country to help with the clean-up, and all the trust's properties were made safe and opened to the public the following spring. An appeal raised £2m from a public shocked by the images of devastation. And behind the scenes, more work was going on. "We started emergency propagation of the rare plants and trees that had fallen, so we could eventually bring back plants to replace them and save rare genetic material," says Calnan. A wholesale trawl of the trust's archives began for the records, maps and plans needed to begin restoration. And, while the initial loss was a terrible shock, it led to a once-in-a-lifetime chance to plant afresh. A new set of photos, taken to mark the storm's 20th anniversary, show a very different picture: green regrowth 30 or 40 feet tall lapping around the isolated 100-footers that survived the winds of 1987.

Ray Hawes, now the NT's head of forestry, had an early warning of the storm's severity at 4am on when an oak tree crashed into the bedroom of the house he had bought in the first week of October 1987, shortly after his wedding. He joined the National Trust in March 1989, when the clear-up was still in full swing. "We had to accept the storm was an occasion where we couldn't control nature," he says. "It changed the thinking in the forestry world."

One lesson was that nature is good at restoring woodland, but cannot replace ornamental features such as avenues. "If trees are blown down, they don't necessarily die – if their roots are still in the ground, their limbs will grow up. At Toys Hill, where a substantial area wasn't cleared, there was much more variation than in the cleared areas."

Some of the storm-damaged woodland contained trees of similar ages; a range of young and old plants is needed for continuity, and this too is paramount as areas are regenerated. The opening up of the tree canopy improved light and gave better access for wildlife, as well as opening up new vistas for visitors.

When the storm hit, Mark Wardle, now the head warden at Slindon, was a trainee. He had just put up his first gate, at a Woodland Trust property; the gate remained standing, though the fence on both sides of it had been smashed by falling trees. He joined the team at Slindon in 1988. "It was an absolute mess, like a bomb site," he recalls. "There were bonfires as big as houses, being loaded by machines half as big as houses. Slindon was renowned for its high stands of beech trees, which people loved. Nearly all of them blew over."

The replanting at Slindon was of mixed species – oak, ash and beech. "It was a massive investment in time and labour: planting, keeping the brambles away and taking the protective tubes off the young trees when they grew larger," says Wardle. "But it is looking very good as a result of all that effort."

If such an event ever happened again, however, policy might be rather different, and consist of managing the natural process of regeneration. "Allowing regeneration rather than replanting means working with nature rather than against it, fighting to keep what you have planted," says Wardle. "In areas of woodland that have grown in corners that were less managed, there are still lovely straight trees, and there were foxgloves everywhere early on before the trees began to grow up again. There have been masses more flowers, more butterflies, beetles, bugs and woodpeckers. Nature responded in a very positive way."

Andy Jesson, head gardener at Sheffield Park, was working as a tree surgeon in Manchester in October 1987. The mass exodus of tree professionals to the South-east in the aftermath of the storm left the North of England short-staffed. One of the legacies of the storm that was still being felt when he joined Sheffield Park six years ago was the loss of the estate's drainage system. The clay drainage pipes had either been lifted by tilting root plates or smashed by falling trees. This had left the heavy clay soil wet and cold, which had hampered planting, so a new drainage system had to be installed and left to settle. Then came the planting of 4,000 new trees and shrubs, including acers, rhododendrons, azaleas and 150 English oaks, restoring the garden to its former glory.

"We are keeping to the plans of the garden laid down over 300 years, using locally sourced seeds and material," says Andy Jesson. "The images of the storm were horrendous. But I believe the garden is more vibrant now, with a younger tree stock."

Climate change has also been taken into account in the new plans. "The shelter belt at Sheffield Park took a real hammering, and protecting the garden from the north-easterly winds is very important. We've tried to climate-proof the new planting, combining drought-loving and moisture-loving trees to hedge our bets," says Calnan.

The Great Storm was calculated as a once-in-300 years event, but, he adds, as climate changes, those odds could shorten. "We think we will have to contend with more frequent storms and we are already noticing this in the North. We may end up with a younger landscape as venerable old trees peter out, we don't know. But there are oaks out there that are up to 600 years old that are resistant and may cope – they have already stuck up two branches to a mini ice-age and centuries of storms."

When the wind blows... the Great Storm in facts and figures

* The Great Storm of 1987, which occurred during the night of 15 October and the early morning of 16 October, wreaked havoc and destruction across southern England.

* Gusts of wind of 70 knots or more were recorded for four consecutive hours. The strongest recorded gust was 100 knots at Shoreham on the Sussex coast, and gusts of 90 knots were recorded at other coastal locations. Even inland, gusts of 85 knots were reported at Gatwick airport.

* Winds brought down millions of trees, damaging buildings and cars and blocking roads and railways. Hundreds of thousands of homes were cut off after electricity and telephone lines were brought down. The storm killed 18 people in England, a ship capsized at Dover, and a Channel ferry was driven ashore near Folkestone.

* A total of 15 million trees were lost in the storm, including 10 million conifers, 3.25 million oaks and 1.75 million beeches. The National Trust alone estimated that it lost over 250,000 trees. Thirty of its properties were badly damaged.

* If the storm had occurred a few weeks later the damage to trees would have been far less. A mild autumn had meant that most trees were still in leaf, and therefore offering more wind resistance. Furthermore, an exceptionally wet autumn meant root systems were sodden and couldn't hold out against the wind.

* An appeal to help the National Trust after the storm raised £2m. The Prime Minister, Margaret Thatcher (right), even donated trees to Chartwell in Kent, the home of her predecessor, Winston Churchill.

* The Great Storm was not a hurricane. A hurricane is the term used for a storm that develops in the tropics, which the Great Storm did not. Hurricane-force winds of 64 knots or more sustained for 10 minutes or more (excluding gusts) did occur but were not widespread.

* Forecasters came in for criticism as little warning was given. BBC weather presenter Michael Fish famously told viewers there would be no hurricane. However, Fish was referring to a tropical storm in the North Atlantic that he correctly predicted would not reach Britain.

Jamie Merrill