Britain's ancient woods are living time capsules of centuries of human exploitation of the environment. How best can we preserve them, asks Ian Rotherham

Our complex and dynamic ancient woods are a vital and irreplaceable resource. Each one is distinctive to its time and place. Even for the untutored, stepping into ancient woodland is a spiritually uplifting experience. Trees and woods balance environmental extremes and the problems of our ever more urbanised and polluted world. They stabilise humidity, filter dust and remove carbon dioxide from the air. We are happier and healthier for the contact.

There has been an increasing recognition of the value of ancient woods in recent years. But for those aware of their history, there is also a sense of reverence and even awe. To walk through an ancient wood - with its plethora of wildflowers, insects, birds, mammals, fungi, slime moulds, lichens and other life - is a spiritual adventure. You walk in the footsteps of the ghosts of the wood's previous inhabitants. The notions of "Mother Earth" and the "Green Man" and a perception of the "wildwood" become almost tangible. This bond between people and trees has led many to join groups and organisations that care for Britain's woodlands.

But the story isn't simple. There is a tension at the heart of these precious sites. In a landscape in flux, woods may be islands of stability for wildlife, for history and for people escaping the madding crowd. But here's the rub - they have an industrial past. They were living and working woods that were vital to local economies over centuries. The gentle scars of these former times are written indelibly into today's woodland fabric.

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Ten years ago, a landmark conference in Sheffield explored the relationship between the ecology and archaeology of ancient woodlands. Before meeting, specialists from several fields surveyed an ancient wood on the edge of the city. The results were remarkable, as were the oversights that later became apparent.

The experts were perplexed by what they saw in Ecclesall Woods. Why, for example, did the core of the wood largely lack the so-called ancient woodland indicator plants such as greater stitchwort and dog's mercury? Why did some species, such as bluebell, seem more abundant than others? Why was topsoil absent from most areas except the edges? The archaeologists puzzled over the bumps, ditches, platforms and pits they had identified. The consensus that emerged was that of a botanically poor woodland typical of local geology that had a modest level of medieval or early-modern industry.

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Ecclesall had been a coppice wood. Small trees were cut back to the stump on a 15 to 20-year cycle to generate "spring" wood for charcoal, whitecoal (which is similar to charcoal but is used in lead smelting) and other products. Large trees were removed for timber used in construction work. A recently cut coppice wood would have looked devastated. But within a year, the wildflowers would be back in profusion. The disruption was generally superficial. But in Ecclesall Woods, the experts found, most of the topsoil and the woodland flora had disappeared.

This had nothing to do with any inherent ecological character - it was all because of people. Centuries of traditional charcoal manufacture had stripped soil and vegetation in controlled burns. The wood's periphery had escaped the burner's spade. Soils, plants and the platforms built into the landscape bore evidence of this activity. And the scale of operation was not modest, as the experts had thought. Later surveys mapped more than 350 charcoal hearths and 150 pits in about 100 hectares. The ecological impact of this industry had been colossal.

Left alone, the woods will change. The scars heal, the glades close and the coppice grow up. As this happens, the darkening canopy of the bigger trees may shade out the bluebells. Some trees die to generate deadwood, others fall to create new glades, and saplings rise to take their place.

Wildflowers cover the platforms, and badgers form setts in the clean charcoal left by the burners.

To maintain these woods on a sustainable basis, it is argued that we must manage them. Perhaps they should even produce an economic return. Indeed, when woods have been economically important, society has protected them - this is why so many survive. But this is not without potential conflicts.

To appreciate the antiquity of many woods, you look for gnarled stumps and twisted trees with rot pockets. And in the deadwood is a habitat that sustains a huge array of threatened wildlife species, from insects to mosses. But modern aggressive woodland management destroys such treasure.

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We don't like untidiness, and a quick swipe of the chainsaw removes a wildlife sanctuary several hundred years old and an irreplaceable archive of site history.

Modern management is usually short-lived and intensive. Often, the chainsaw and the tractor are the mode of operation. To make it profitable, a big old tree may be offered to a contractor as a "sweetener". The impact is immediate, long-lasting and coarse-grained.

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Woods are living time capsules, each presenting a timeline through history.

If we stop the clock and manage the site for a particular period, when should it be and who should choose? Today's woodland manager might have just a five-year commitment to a site that has a lineage stretching back 3,000 years or more - a sobering thought.

Last week, experts and practitioners met once again in Sheffield to debate these issues. Informed opinions and up-to-date research addressed some of the big controversies and raised fundamental questions about the nature of wooded landscapes. Landscape ecologist Frans Vera, for example, argued that northwest Europe's wooded landscapes were historically more dynamic and more affected by large grazing herbivores than previously thought. This theory prompted a surge of interest and will have significant impact on management issues as England's deer population is expected to double in the next decade.

Another question for the future is whether ancient trees could themselves be deemed archaeological treasures and be listed as ancient monuments.

Shouldn't all trees more than perhaps 200 years old be protected to generate the majestic veterans of the future, as well as deadwood vital for rare species?

Understanding the past to inform the present and influence the future of our ancient woods is the key. The message is getting out. Several books will be produced from the papers presented at this meeting, and a field manual of woodland archaeology is to be published, with supporting training seminars. These initiatives bode well for the future and will have a resonance and an influence on all who care about their local ancient wood.

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Excitingly, of course, there is one near you.

Ian Rotherham is principal lecturer at the Centre for Environmental Conservation and Outdoor Leisure at Sheffield Hallam University.