Once it was the avocet and the osprey. Now it's the rhinoceros hornbill and the rufous-collared kingfisher, not to mention the great argus pheasant and the red-naped trogon. Britain's Royal Society for the Protection of Birds (RSPB) is enlarging its vision, from the denizens of the Suffolk marshes and the Scottish lochs to the living jewels of the Asian rainforest. The society is moving into tropical bird conservation in a serious way as part of a partnership that is seeking to save one of the world's greatest wildlife hotspots.

With its sister organisation in Indonesia, and BirdLife International, the RSPB has secured a long-lasting management concession on a stretch of lowland rainforest in Sumatra which has more breeding bird species than all of Britain. In an area two-thirds the size of Greater London, the Harapan rainforest hosts at least 267 types of bird, compared with 226 in all of the British Isles - and may hold more than 300.

And that's just the birds. It is also home to a striking range of animal species including Asian elephants, Sumatran tigers and the newly discovered clouded leopard, as well as five primate species, sun bears, Sumatran otters, Malayan porcupines - and the world's richest and most diverse flora.

Yet for all its natural treasures, the forest has been placed under dire threat by the pressures of illegal logging and conversion to timber and palm oil plantations, which have reduced the Sumatran rainforest to a fraction - less than 5 per cent - of its former 16 million hectares.

For the past five years, the RSPB and BirdLife have joined with Burung Indonesia, the local bird protection organisation, in lobbying the Indonesian government to allow the Harapan forest, two hours' drive from the town of Jambi in the centre of the island, to be protected.

Two years ago, the government agreed in principle the area could be saved; then the partnership won the management concession by outbidding logging companies; and now the concession has been extended from 20 to 100 years, meaning the forest, which has been partly logged, finally has a chance to recover and regenerate fully. "It is difficult to express just how significant this breakthrough is," said Graham Wynne, the RSPB chief executive.

"Almost all of Harapan rainforest has been logged to some extent in the last 60 years and some of its species have been staring extinction in the face. But all of the forest can still recover and, thanks to the work of Burung Indonesia and the Indonesian government, every single species it hosts now has a toehold on survival. Harapan rainforest is to become a beacon of hope for forests across Indonesia and beyond."

Until now, sites earmarked for timber production or plantation crops in Indonesia could be used for nothing else. But the ecosystem restoration decree, which was introduced by the Indonesian Ministry of Forestry, permits the management of forests to obtain benefits labelled "ecosystem services". These include storing carbon, controls on pollution and protection for wildlife, all of which, say the partnership, will help nearby human communities.

Directly benefiting will be the 150-strong Batin Sembilan tribe, a nomadic people that will continue to harvest rubber, honey, fruits and rattan for its own use. "Now these people have a choice for their future. With intact forest remaining, they will have the choice of maintaining their traditional lifestyles," said Sukianto Lusli, executive director of Burung Indonesia.

"They will also have the option of becoming wildlife monitors or forest wardens, as will other people in the local area." There will be other jobs for the Harapan community including forest guides, nursery management and the preparation of land. Field staff are being recruited now and the site will eventually be managed by a team of about 80 people. The development of a research station and eco-tourism are long-term possibilities.

Once they start looking properly, conservationists expect to find thousands of plant and animal species in Harapan. While Sumatran lowland rainforest is already known to boast a more diverse flora than anywhere in the world, there are also at least 37 species of mammal and at least 33 amphibian and reptile species, including the endangered spiny turtle and Asiatic softshell turtle.

The Storm's stork is the most threatened bird species found so far - there may be only 250 left in the wild. Of other birds found in Harapan rainforest, 66 are at risk, including the rhinoceros hornbill, rufous-collared kingfisher and great argus pheasant mentioned above. Up to 30 more bird species could be identified in new surveys later this year.

Mr Lusli said: "We expect big dividends for wildlife from this project. Sumatra's lowland forest is already a hotspot for rare species and this initiative will make it even better. It will bring hope for species at risk of extinction." There are between 100 and 300 critically endangered Sumatran tigers still in the wild, of which about 20 are in Harapan. The Sumatran tiger is a sub-species of the Asian tiger. The Caspian, Javan and Bali tigers became extinct in the 1900s.

"Indonesia suffers from some notoriety for its rapid deforestation," said Marco Lambertini, director of network and programmes for Cambridge-based BirdLife International. "However the Harapan rainforest initiative, and the Indonesian government's support for it, could mark a turning point for the country's forests, a new hope for their conservation.

"Their biodiversity, their role in the mitigation of global warming as well as regulating local climate and preventing floods, make their protection relevant for both the local as well as the global community. "We will work towards every success in this initiative, and hope that others follow." Graham Wynne said: "This is a groundbreaking project achieved with the full support of the Indonesian government. It is hugely significant not just for rainforest conservation in Asia but for other parts of the world."

Harapan is, in fact, the Indonesian word for hope. The forest stretches 35km (22 miles) east to west and 40km north to south, and represents about 6 per cent of remaining lowland rainforest in Sumatra. It is two degrees south of the equator and conservationists hope that its humid conditions will hasten regeneration. Furthermore, the ecosystem restoration decree means other private management bodies also can apply to restore forests in Indonesia.

Five sites were shortlisted before the Harapan area was chosen for the protection campaign; it was selected for its wildlife diversity, the quality of its flora and its accessibility. "One of the reasons it was identified as the best was that human pressure is not so heavy," said Dieter Hoffmann, the RSPB's head of global programmes. "Access was reasonably good and the forest itself is in reasonably good condition. But most of all, the biodiversity is spectacular. In terms of flora, it is the richest habitat in the world - richer than the Amazon."

The RSPB is about to launch a UK fundraising campaign for Harapan with a target of £2 million over the next 12 months. Similar campaigns are beginning in other European countries and Japan. The initiative has already received significant financial support from the European Commission and Conservation International's Global Conservation Fund. In the long term, the RSPB, Burung Indonesia and BirdLife International plan to establish a trust fund of £9m. Annual interest payments from the fund will cover the forest's management costs.

To give an idea of the size and scale of the new project, the total area of all the RSPB's 200 bird reserves in the UK, including Minsmere in Suffolk (where the avocet, the beautiful black-and-white wader, returned to breed more than half a century ago) and Loch Garten in the Scottish Highlands (where the osprey, the fish-eating hawk, returned at roughly the same time), is 131,000ha (325,000 acres). Harapan alone is 101,000ha.

Twitcher victories: a history of the RSPB

The return of the avocet and the osprey, charismatic species that had been extinct to Britain as breeding birds, have hitherto been the most spectacular milestones in the 116-year history of the Royal Society for the Protection of Birds. In each case, the society facilitated the return by buying and wardening the land on which the birds were nesting, on the Suffolk marshes in the case of the avocet, and in Scotland's Spey Valley in the case of the osprey.

It was in the late 1940s and early 1950s that the two lost species tentatively re-established themselves, and they have now gone on to have healthy populations that have spread across the country. Both have become symbols of the RSPB's success as the largest wildlife conservation charity in Europe, with just over a million members. (Indeed, the avocet, with its slender upturned bill, is in the society's logo.) The rise in membership has been remarkable, with two great surges: between 1969 and 1976 it rose from 50,000 to 200,000, and from 1989 to 1997 it rose from 500,000 to a million.

Other achievements have been the Big Garden Birdwatch, in which nearly half a million people took part last year, noting what birds appeared in their gardens, and the defeat in 2003 of plans to build an international airport at Cliffe on the North Kent marshes, which would have damaged important wildlife habitats. The RSPB was founded in 1891 by women concerned at the killing of birds such as great-crested grebes for plumage for women's hats. The Duchess of Portland, the first RSPB president, held office from 1891 to 1954.

(Por Michael McCarthy, The Independent, 04/04/2007)