Rural: How green was my mountain - or soon will be

The farm is so wild, no one even knows how big it is, but David Henry has great hopes for his new home on Green Mountain in Ascension Island. Duff Hart-Davis meets a modern pioneer.

None but the most intrepid would take on a 10-year lease of Green Mountain Farm, wrapped round the summit of the volcano that is Ascension Island in the South Atlantic. Yet David Henry, a stalwart 37-year-old born in London of St Helenian and Irish parents, has done that very thing.

Only those who know Ascension can fully grasp the size of his project, for the farm - clinging to precipitous slopes between 2,000ft and 3,000ft above sea level, at the top of 19 tortuous hairpin bends - has never been fully under control, and has lain abandoned for years.

To start at the beginning: in 1817 the island was occupied by the Royal Navy to prevent the French from using it as a base for rescuing Napoleon, incarcerated on St Helena, 700 miles to the south east. Ascension was then a forbidding place, with rust-red volcanic cones rising from deserts of tumbled black lava, and no plant life except near the top of the highest peak, which sailors naturally called Green Mountain.

For the next century the island remained a naval base, run by the Royal Marines who, as a sideline, made immense efforts to cultivate part of the mountain to provide fresh food. Then, as now, two distinct climates prevailed. Down on the lava plains the temperature was in the high 80s all year round, with a south-east trade wind blustering over the lava. High up, the air was far cooler, and the mountain caught the moisture of passing clouds.

Severe handicaps limited agricultural progress. One was the sparse rainfall, which some experts believed could be increased if "the direction of the electricity were reversed" by convicts whirling chains on the summit. Another snag was that with scarcely any native plants or animals there were no natural controls, and one imported species after another ran amok.

Rats had already come ashore from wrecked ships, and were living off seabirds. To suppress them, the Marines brought in cats, but these soon escaped and went wild, so the Navy imported dogs to hunt them down. Goats, sheep, pigs, and donkeys also made off into the lava deserts.

Up on the mountain, the Marines established a little farm. Many imported plants and trees died; others rampaged, and plagues of insects and mice ravaged garden crops. From their comfortable base in London, 4,000 miles away, the Lords of the Admiralty directed the deployment of corrective measures: mynah birds, starlings, rooks, pheasants, partridges, ducks and hedgehogs were sent out to eat the insects, and barn owls to catch the rats and mice.

Professional gardeners were driven to despair by repeated setbacks - and none more pitiably than Joseph Spearing, who in 1887 had to be taken away "in a condition of quiet dementia", suffering from what was described as "formication"; he believed that "not only his bed but his whole house was swarming with ants".

When the Marines left the island in 1922, the farm was maintained after a fashion by their successors, the Eastern Telegraph Company, forerunners of Cable & Wireless, but in the past few years it has gone sadly downhill. Enter David Henry, a carpenter by trade, but now also a farmer, who in the spring of 1982 went out for a holiday to St Helena, and was marooned there for seven months because the ship that serves the island was commandeered for the Falklands war. As St Helena has no airfield, the only way he could return home was by hitching a lift on a Danish vessel, which called at Ascension.

That visit gave him his first sight of Green Mountain. He later made many return visits to St Helena and on his way home he several times called at Ascension, taking advantage of the fact that RAF Tristars regularly pass through on their way to and from the Falklands garrison.

Then, earlier this year, the authorities decided to advertise Green Mountain farm for let, and David was the successful applicant. His only rent is a commitment to maintain the farm as a recreational area for the temporary residents who live and work down below. (These include British and American personnel, and a considerable staff of workers from St Helena, known to all as "saints".)

His tenancy agreement encompasses all the land more than 1,900ft above sea level, and with it several buildings constructed by the Marines. Some indication of the farm's wildness is given by the fact that nobody knows how big it is. David estimates it as between 10,000 and 20,000 acres, but there is only one half-acre patch that could reasonably be called flat, and perhaps 50 acres that could be brought into use for market gardening, "if I work really hard".

That is what he proposes. He is now in St Helena, but later this month will bring his fiancee Melanie Timm, a veterinary nurse and livestock officer, to live on Green Mountain for the foreseeable future.

The challenge, in which he rejoices, is to sort out the astonishing ecological jumble left behind by the Marines and their successors. Ginger, brambles, aloes, bamboo, acacia, casuarina, wild raspberries, all grow together. Already he has discovered an overgrown coffee plantation that can be brought back to fruitful life. A flock of 1,800 sheep, loose on the mountain, will have to be corralled, culled, and rejuvenated by introducing pedigree rams. Down below, wild donkeys still roam the lava, living largely on cardboard and hats blown off unwary islanders by the trade winds.

One factor in David's favour is that on the mountain rainfall has definitely increased, apparently in response to the spread of trees and shrubs. Now vegetable seeds leap up within three or four days - but so also do weeds.

The new incumbent has ambitious plans for supplying not only the plain- dwellers and the island ship on its way up and down the South Atlantic, but also the "saints" who work in the Falklands garrison, and would welcome regular deliveries of pumpkins, yams and sweet potatoes. He even has his eye on markets in London. With the RAF air-bridge in place, with fax, telephone and soon (he hopes) the Internet connected to his eyrie in mid-ocean, he could perhaps establish a mail-order business, to give customers "direct access to what is probably the cleanest farm in the world".