Another branch of the keep-fit movement

Benjamin Mee joined holidaymakers who pay good money to do gruelling conservation work

'It's almost as if they've got consciousness," said Gordon, throwing a twisted stem as thick as his arm on to the fire that he and Trevor had spent most of the morning trying to get going. Now it was healthily ablaze and easily able to consume such a large, wet piece of wood, which only a moment ago had been growing out of the ground.

'It's almost as if they've got consciousness," said Gordon, throwing a twisted stem as thick as his arm on to the fire that he and Trevor had spent most of the morning trying to get going. Now it was healthily ablaze and easily able to consume such a large, wet piece of wood, which only a moment ago had been growing out of the ground.

"Sometimes you pull it, and there's a pause, then it pulls back," said Gordon. "Or you pull it and its mate behind you smacks you across the face," laughed Trevor, a 12-year veteran of "action break" holidays with the British Trust for Conservation Volunteers (BTCV).

Rhododendron ponticus is an attractive flowering shrub favoured by the Victorians, who imported it from Nepal to decorate their formal gardens. But the shrub is not just a pretty face. Its stems re-enter the earth and re-sprout every 18in or so - a process called layering if it had been carried out by human hand - creating a canopy that blocks light and prevents anything else from growing. Seeds can travel up to three miles, and, for good measure, the rhododendron sheds toxic leaves into the topsoil, killing even mosses and lichen as it enforces its monopoly of nutrients. A century-and-a-half in ideal growing conditions has allowed huge, coiling clumps of the plant to take a grip on large swathes of British woodland.

"It's got something of a stranglehold around here," said Mat, a full-time BTCV volunteer, gesturing across the valley to Ardross Castle, a Victorian fantasy in red stone that bristles out of the forest just north of Inverness like the antlers of a stag. Between us and the castle a dark-green cover undulates about 6ft off the ground, allowing only the larger birches and pines to survive. All around lie the decomposing husks of smaller trees, themselves now colonies of rich carpets of moss six inches deep.

After a day with a bowsaw battling the writhing ligatures of p onticum, witnessing its dominance over all other life forms at close hand, I was inclined to agree with Gordon about the plant having consciousness. Working into the damp, dark hearts of these formidable bushes, which fan out 30 to 40ft from their trunks, and then severing their limb-like stems, felt more like killing a creature than cutting back a plant. But this feeling was more than countered by the satisfaction of introducing sunlight to parts of the forest floor that hadn't seen the sky for many years.

Heaving a large bough up a slippery, 30-degree slope and throwing it on to Trevor and Gordon's fire was also very satisfying, as was simply being outside in the woods on such a lovely day.

Biophilia is the newly-coined term for the feeling of well-being that comes from spending time in green, open space, and it is something the BTCV has begun to realise they can market. Laboratory research shows that someone just looking at a picture of a tree experiences a relaxing effect, so spending a week or a weekend away working in among them must have untold benefits.

Dr William Bird, a confirmed biophile, began prescribing afternoons at the "green gym" - his local BTCV volunteer group at Sonning Common, which meets twice a week - for patients needing exercise who had dropped out of his gym referral scheme. "The drop-out rate fell from 80 to 12 per cent," said Dr Bird, "because as well as exercise people were getting the psychological benefits from working together as a group, achieving something tangible, and being out of doors - all at the same time."

"It gets people working without them realising it," said Veronica Reynolds, a researcher at Oxford Brookes University. Comparing activity levels against a step aerobics class, she found people were spending longer in the training zone, achieving higher heart rates and burning more calories an hour. But their perceived exertion rate was much lower. "If we asked them whether they were working hard they'd say 'no', though the heart monitors told us they were actually going for it harder and for longer than a step class."

At Ardross Castle, 10 grubby people on action breaks had returned for lunch, faintly steaming and firmly bonded after seven days holed up in what appeared to be a derelict scout hut. They were there for 10 days, we for only two, and we felt like newcomers on the set of Big Brother. We made up for the intrusion, however, with news of what was happening in the real television programme, which they craved. Watching them washing, changing clothes and fixing lunch, we knew what it must have been like for missionaries travelling up river to outposts where the expats have gone native.

The afternoon was spent in mortal combat with the phantasmagoric p onticum. In the evening, Hide (pronounced Hee-day), a Japanese architecture student, cooked a delicious chicken and rice dish, after which the party began telling stories of other all-action holidays they had been on. Matthew, a boyish 40-year-old IT worker, had tracked snow leopards in Nepal with Earthwatch. "There are parts of the Himalayas where you are always being watched by a snow leopard," he told us.

We were invited to stay in the "chalet", but, being fresh from the outside world, we felt we hadn't yet quite earned the right to this luxury. They kindly offered to budge up - "no, really" - but to us their unfurnished 10ft by 6ft rooms looked a bit like empty sheds into which someone had emptied Gro-bags, then trampled in and out wearing wet boots for six days. We stayed in a B&B.

The next day, we returned to the fray, discovering larger and ever more alarming plants as we moved deeper into the forest. Working for long stretches on my own, I found myself reminded of Sigourney Weaver in Alien, as the magnitude of what she was up against slowly dawned. I asked Hide about his thoughts as he worked alone. "I am solving the puzzle," he said, straddling a vast knot of stems. "You must use this part of your body," tapping his head.

"And I am enjoying the circumstances," he added, gesturing to the fast-flowing river below.