Come mid-December, the peace and quiet of Wilderness Wood is broken only by the sound of birdsong and the giggles of two young boys, hopping excitedly as their father saws doggedly at a tree trunk. Where bluebells bloomed around the 5,000 firs on this hillside plantation in spring, now there is a dusting of snow to add to the festive feeling.

Anne and Chris Yarrow, who own the wood, have been growing Christmas trees here since they bought the woodland in 1980. They allow 700 trees to be harvested from the half-hectare plantation each year and trees can be reserved from the beginning of November. A label attached to the tall leader stem identifies the owner, but some familes have gone further - marking their tree by decorating it with red bows or tinsel; one even sports a photo of the family dog in a Santa hat.

The Yarrows grow four varieties. The traditional Norway Spruce copes best with the sandy, acidic soil here. Down the hill, Chris points out the Douglas Fir, a fast-grower that needs pruning three times a year. It has soft needles, making it ideal for families, and a lovely citrus scent. There's Nordmann Fir, too, a popular non-drop variety and by the bottom fence, a crop of Blue Spruce, famous for its hard needles and pungent smell.

Anne and Chris buy around 1,000 two-year-old transplants each year and plant them in March. Sadly, a third will die, due to summer drought or roots failing to establish on the poor, shallow and badly drained soil. The remainder will take five years to grow to saleable size (1.5-2 metres). 'It's fast in forestry terms,' says Anne. 'It means we can generate some income from the trees in a relatively short space of time.' The trees are pruned twice a year, in February and July, leaving 30-45cm of their annual growth of a metre or so. Chris adds lime to the soil once or twice a year to balance the acidity and sprays against mites and aphids in winter and summer.

The Yarrows sell around 2,400 trees each year, so some 1,700 are bought in from local growers to meet demand. 'We could grow more, but we don't want to turn more of Wilderness Wood into a Christmas tree plantation,' says Anne. In the yard, customers poke about amongst the banks of Norway Spruce, heaving them out and assessing their bushiness. 'At a garden centre trees are uniform in shape and size, like Granny Smiths in a supermarket,' says Chris, 'but people can pick all shapes of tree here.' With the barn decorated in twinkling lights and a pine fragrance in the air, tree buying feels more like a festive event than a simple purchase, which probably explains why 85% of Christmas tree sales are to returning customers.

Most tree-buying excursions culminate in a trip to the barn, which is both shop, visitor centre and tea room. People sit at big tables or on squashy sofas around the wood burner, nursing a hot chocolate or mulled apple juice, while in the gift shop there are folksy Christmas cards, wooden decorations and felt stockings to choose from. Outside, foliage, wreaths and misletoe are piled along a bench,and there are logs and fence posts for sale in the yard, alongside beautiful wooden products, from bird feeders to benches, made in the workshop.

There's something wonderfully low key about Wilderness Wood, but this belis all the hard work that has gone into making a success of this 25-hectare site. Chris's background is in forestry and until a few years ago he ran an arboricultural consultancy alongside the wood. Anne has a degree in conservation. Their vision for Wilderness Wood is the same today as it was at the start: an education and recreation facility, which also produces timber, provides employment and preserves wildlife. Just forestry, they believe, would be an under-utilisation of the land.

Quiet enjoyment is key. Families come to walk, picnic or attend one of the many events, from an autumn fungi foray to a coppicing course. Their impact on the woodland is minimal, thanks to the rigorously sustainable approach the Yarrows have always taken. 'We were as green as possible before it became popular,' says Chris. 'We are very much the product of the Seventies self sufficiency drive, lampooned in The Good Life.' So you won't find paper towels in the toilets or big-name brands in the tea room. The barn and house are heated with waste wood, food is sourced locally and leftovers fed to hens or composted.

On becoming owners of the wood, it took the Yarrows two years to tame it, clearing tracks and establishing footpaths. At the time they lived in Lewes, with daughters Joanna and Kate, then six and three, but moved to a caravan in the wood at weekends. 'We got ourselves known as amiable eccentrics,' says Chris. Building the barn, the first construction on the site, contributed to this reputation. It is made of materials grown in the wood - oak for the beams, sweet chestnut for the shingles, pine weatherboards and hazel wattle coated in traditional daub for the walls. 'We got a recipe from the Weald & Downland museum and used local cow dung to make it,' says Anne. It looks medieval, but is in fact just 27 years old.

The barn set a precedent for the house they hoped to build. 'In order to run a business like this we really needed to be on the spot,' says Anne. 'With the barn, the planners could see what we were about.' Anne and Chris designed their home with an architect friend, won planning permission in 1982 and completed it a year later, doing much of the labouring themselves. None of this would have been possible without local support and the couple were careful to involve the community at every stage. Most importantly, perhaps, they made the wood available to them, free of charge. 'We have up to 10,000 visits by non paying locals each year now. We are the village park,' says Chris.

From a few hundred people when it opened in 1982, Wilderness Wood now welcomes 26,000 paying visitors annually. School trips, special events and around 300 woodland birthday parties are hosted here each year. Managing the woodland takes place alongside the visits and parties. Coppicing the sweet chestnut is done in 15 year rotations, with half a hectare cut at a time, while maintenance work, from clearing footpaths to repairing steps, is a year-round occupation. To help, the Yarrows employ a team of three full-time staff and a handful of part time, all talented in a number of fields, from tree felling to teaching. 'The joy of a place like this is that you are never doing anything for more than a few hours,' says Chris. 'You have to be multi tasked.'

It was never the Yarrows' ambition to make a huge income from the wood. 'We just wanted to tick over,' says Anne. For them, Wilderness Wood is a lifestyle rather than a job. 'Very few people have the chance to run their own business, design and build their own house, be their own masters. The wood has given us all those fantastic privileges,' says Anne. And when they close their doors on December 24th and settle down to a quiet family Christmas, they have the satisfaction of gathering around a tree grown just metres from their door.