Twenty years after the killing of Chico Mendes, one of the world's most prominent rainforest defenders, hundreds of human rights and environmental activists still face the threat of assassination in Brazil, a new study claims.

The report, compiled by Brazil's Catholic Land Commission (CPT) and due to be released in full early next year, reveals that at least 260 people, among them a Catholic bishop, live under the threat of murder because of their fight against a coalition of loggers, farmers and cattle ranchers.

The list names Frei Henri des Rosiers, a French priest based in the Amazon town of Xinguara, as a particular target. Police are investigating claims he has a £14,000 price on his head because of his fight against slave labour. Also named are Maria José Dias da Costa, a union leader in the remote town of Rondon do Pará, and an Austrian bishop, Dom Erwin Krautler, who has been under 24-hour police guard for two years because of his battle against developers and child prostitution in his Amazonian diocese.

In February this year, Francisco da Silva, a 51-year-old leader of the landless movement in the Amazon, was killed with a single shot to the head. He had been named in a previous CPT report about rural leaders receiving death threats.

On Monday night the Brazilian president, Luiz Inácio Lula da Silva, is expected to address the country on television to pay homage to the life of Mendes, a rubber tapper turned environmentalist who was gunned down outside his home on 22 December 1988. Lula's address is part of a wave of tributes across Brazil, from marches on the streets of Rio de Janeiro to celebrations in his hometown of Xapuri. But while his standing as a symbol of protest is not in doubt 20 years on, environmentalists and human rights activists are divided on Mendes's practical legacy.

In September this year government figures showed that deforestation in the Amazon had risen by 64% over the previous 12 months. Earlier this month, members of Ibama, Brazil's environmental taskforce, discovered that nearly 3,000 hectares (7,410 acres) had been deforested, mostly illegally, inside a reserve named after Mendes. "Each year on 22 December I ask myself if he died in vain or not. And today, after all these years, the answer is not yet clear to me," said Alfredo Sirkis, a prominent member of Brazil's Green party and friend of Mendes.

Sirkis said: "I won't say that nothing has improved," but he added that the last 20 years had seen a "continuation of this project of devastation".

Born in the remote Amazon state of Acre on 15 December 1944, Francisco Alves Mendes Filho followed in his parents' footsteps early in life, becoming a rubber tapper at the age of nine.

By the mid-1980s he was spearheading protests against local cattle ranchers and their gunmen, who sought to tear down the forest and drive out the impoverished rubber tappers. Renowned for visionary views on sustainable development, Mendes quickly became a poster-boy for the international green movement, travelling to the US to lobby against infrastructure projects he believed would devastate the Amazon.

"He knew how to talk to the rubber tapper in the middle of the forest in the same way he knew how to talk to a technocrat from the World Bank," said Sirkis. His murder turned him into an eco-martyr both at home and abroad, and catapulted the issue of rainforest destruction further up the international agenda.

"Chico left a great legacy," said Brazil's former environment minister, the senator and former rubber tapper Marina Silva. "Twenty years on, the environmental question has gained strength across the whole world."

She added: "He was a guy that spoke of things which were ahead of his time ... [and he] made me want to be part of that fight."

Bishop Krautler agrees: "It was never in vain. In death he [Mendes] spoke even louder than when he was alive."

Soon after his death, Brazil's government began introducing the "extractivist reserves" of which Mendes had dreamed. The reserves were areas of rainforest where local populations could earn their living while simultaneously protecting the environment. The first, created in 1990, was named after him and now covers 11m hectares of land.

Chico Mendes: Martyr for our times

When I heard, 20 years ago this week, that Chico Mendes, leader of the Brazilian rubber tappers' union, had been murdered, I was sad but not surprised. The last time I saw Chico, five months earlier in the town of Xapuri in the western state of Acre, he told me the ranchers had already tried to kill him six times.

Looking at my notebooks, I now notice that Chico actually named the man later convicted of organising his killing: Darly Alves da Silva, a rancher who has not been seen since escaping from jail where he was serving a sentence for the crime.

Darly already had a murder charge against him in another state, something Chico reported to the police.

It was when Chico's union successfully defended a piece of virgin rainforest sprinkled with rubber trees against the ranchers' attempts to claim it that the struggle became personal. Before the shooting of Mendes only 10 people had ever been brought to court for around 1,000 murders in the Amazon in the 1980s.

But Chico was different and his murder sparked an international furore.

In his speeches he used to say: "Come here and kill me. My chest is open." He knew he might achieve more by his death than he had by his life.

Today the extractive reserves Chico championed are relatively successful in protecting parts of the Amazon, as are reserves run by the rainforest's indigenous people.

Now people talk of using carbon credits to protect similar areas around the world. And I realise that I had met the martyr for our times - the Gandhi, or perhaps the Che Guevara, of our environmental age.

Charles Clover