Wangari Maathai has spearheaded the planting of billions of trees across the world and is now leading the fight to save the world's second largest forest, in Congo. Photograph: Martin Godwin
Wangari Maathai's office in fuming, downtown Nairobi is full of citations and mementos, but there is one special photograph. It's of her and Barack Obama planting an olive tree in Uhuru park in the city centre in October 2006. It could be any two celebrities posing for a routine photo call, but there is a strong connection between the spiffy, young American senator on his way to the White House and the flamboyant older woman dressed in canary yellow who had just become the first African woman to win a Nobel prize.
The link between them is known as the "Lift". In 1960, 300 Kenyans were awarded Kennedy scholarships to study at US colleges and universities. One of the first was a 22-year-old economics student called Barack Obama, a Luo from west Kenya who was picked to go to a college in Hawaii. With him was Wangari Maathai, a 20-year-old Kikuyu from the highlands heading for Mount St Scholastica college in Atchison, Kansas. Both stayed in the US for five years and both returned personally transformed to a newly independent Kenya.
It was a heady, liberating time. Obama Sr had just married a Kansan and fathered the boy who is now US president. Maathai returned with a masters and "a determination to work hard, help the poor and watch out for the weak and vulnerable". The spectacular results of the scholarship simply reflect, she adds, the potential of people anywhere to flourish if given the opportunity. In London this week for Prince Charles' climate change meeting with 20 Nobel laureates, Maathai, now nearly 70, cut a lone, if flamboyant, figure: she was the only woman, and with Wole Soyinka, one of only two Africans. Yet, she pointed out, it is women and Africans who must bear the brunt of climate change and pay for the west's profligacy. (About which, she had some interesting points to make. "You must understand that what is happening in the west with the credit crunch has been happening for decades in Africa," she told her audience. "The banks are not regulated. We cannot access money, and only a few people can buy houses. Europe is catching up with Africa. When we were campaigning against African debt we were told that it could not possibly be paid off. Many countries collapsed." As for western democracy, and Britain's parliamentary crisis, "the elites have become predators, self-serving and only turning to people when they need them. We can never all be equal, but we can ensure we do not allow excessive poverty or wealth. Inequality breeds insecurity.")
And while the scientists, academics and politicians talked of technological shifts and the need to bring the best brains in the world to bear on the problem, the former professor of biology at University of Nairobi said bluntly that the answers were known. "We all know what to do. Why don't we do it? The question is, how are we to ensure something is done?"
The reality, Maathai says, is that of the nine billion people expected to be on the planet in 2050, eight billion will be in what are now developing countries. "Climate change is life or death. We could be accused of being alarmist, but if we have faith in science then something very serious is happening. Climate change and global warming is the new global battlefield. It is being presented is as if it is the problem of the developed world. But it's the developed world that has precipitated global warming. There will be a much greater negative impact on Africa because of its geography. But instead of adapting we are scraping the land, removing the vegetation and losing the soil. We are doing things to make it worse.
"Besides, it's in the interests of the rich to help Africa adapt to climate change and preserve its forests. By allowing them to be destroyed a lot of the efforts made in the rich world will be negated and undermined."
Maathai links ecology and culture and argues that the challenge for Africa (the title of her new book) is to look to itself and reclaim not just the land, but its cultures and resources. "If the soil is denuded and the waters are polluted, the air is poisoned and the mineral riches are mined and sold beyond the continent, nothing will be left that we can call our own. Our real work is reclamation - bringing back what is essential so we can move forward. Planting trees, speaking our languages, telling our stories are all part of the same act of conservation. We need to protect our local foods, recall our mother tongues and rediscover our communal character."
Instead, "some Africans are asking themselves whether we are being exposed to a new wave of colonialism," says Maathai. "Yes, there is a grab for resources. We are vulnerable to anyone who wants to exploit us. It's like the 18th-century. Africa finds herself with raw materials but does not have the ability to add the technology. She cannot control the process. So she grinds herself without cash. Africa is paying in raw materials. She pays with her soil. In the past people entered Africa by force. These days they come with similarly lethal packages, but they are camouflaged to persuade Africa's leaders and people to co-operate."
The paymaster these days, she says, is China, which has invested tens of billions of dollars in the last decade to extract African oil, minerals, timber and land in return for roads and jobs. "China is really no different from the United States, the Soviet Union and the colonising European nations which facilitated the rise of African strong men and protected them in the post-colonial period, despite knowing of their corruption and cruelty, so they could continue to extract Africa's resources unhindered. If Africa had spent 40 years investing in education, acquiring skills, she would be in a better position now."
Maathai is western and African, local and international, a member of the elite and someone with a rural background, educated both in one of the world's richest and in one of its poorest countries. But her roots are in Ihithe, a village of peasant farmers near Nyeri in the foothills of the Aberdare mountains. The family home, where her sister now lives, nestles in a deep valley. There's a school, the By-Grace cafe, a few hundred houses, sheep on the roadside and tea plantations everywhere.
"Mother lies there," she says. "My relations live there. It's heaven. But people there do not appreciate it because we have a political and economic system that does not allow people to appreciate the beauty of where they live. That's the tragedy of poverty."
The changes that have taken place in Ihithe since the 1950s reflect the linked environmental and social crises now burdening so much of Kenya and the rest of Africa, she adds. "I have seen huge changes. The population has grown enormously. All that area [around Ihithe] was wooded. There were small farms, full of maize, millet and sorghum. The rivers were huge and clean. There was no tea. Today we see tea, tea, tea. Mother never planted tea. Tea has become slave labour. Farming has become the production of a commodity which people cannot process or eat. You cannot process your own tea. Tea without good governance is serfdom and only leads to environmental and social problems."
But above all, she says, there has been deforestation, with the family woodlots grubbed up to plant tea and the hills all around denuded for firewood. Realisation that communities were destroying their own resources led her to start the Green Belt movement. What began as a few women planting trees is now a network of 600 community groups that care for 6,000 tree nurseries. They have together planted at least 30m trees on degraded private and public land, in reserves, and in cities all over Kenya. The movement, which operates in 30 countries, is far more than a tree planting scheme: it has become an unofficial Kenyan agricultural advice service, a community regeneration project, and a job creation plan all in one.
"There is a change taking place. We can hardly keep up with the requests [for help]. The tree is just a symbol for what happens to the environment. The act of planting one is a symbol of revitalising the community. Tree planting is only the entry point into the wider debate about the environment. Everyone should plant a tree," she says.
Since she won the Nobel prize, tree planting has become an essential for all countries wanting to flaunt green credentials. In 2007 she fronted a UN plan to have 1bn trees planted throughout the world. Over 3.1bn have now been planted and the target has been revised to 7bn - one for every person on earth with a few left over - by the end of 2009.
In a tumultuous life as a pro-democracy and environmental activist, Maathai has been arrested many times, imprisoned, beaten, gone on hunger strike, had to barricade herself into her house to keep the police out, stood for president and been elected an MP. Her personal life has been equally stormy. She and her MP husband, who have three children, divorced years ago: he said she was much too strong-minded for a woman and that he was unable to control her. She called the divorce judge "incompetent" and was given six months in prison for contempt.
Now she is trying to protect the Congo forest, the world's second largest stand of trees. If the Congo goes, she says, not only will tens of millions of people lose their livelihoods, but the climatic effects would be catastrophic and be felt as far away as Britain and the US. Britain and Norway have together put up £100m but it means working with some of the most war-ravaged and corrupt countries and companies on earth.
Ten African governments have asked her to their representative in the Congo basin initiative. "I know they want to take advantage of the peace prize and raise the public awareness," she says. "I know there is apprehension. But refusal to take up the challenge [of the Congo forest] would be wrong. I have no illusions. But there is no option." In the end, though, aid is not the answer. "Donors come to be seen as Santa Claus, bringing with them money, materials and input. The people clap and dance in welcome until the tap runs dry. At the same time, donors' money can corrode responsibility. An attitude exists that one does not have to accountable for the use of funds that have originated outside the country. Individuals and governments misunderstand or subvert the donors' intentions."
Her message in London this week has been fierce and urgent. "Nature is still being taken for granted. Yet when it is destroyed, life itself goes. Politicians [everywhere] are putting immediate needs ahead of the long term. We must challenge the decision makers. We must appeal not just to their heads, but to their hearts. I can only see getting worse things if we do nothing."
• The Challenge for Africa: A New Vision, by Wangari Maathai, is published by William Heinemann (RRP £20). To order a copy for £18 with free UK p&p go to guardian.co.uk/bookshop or call 0330 333 6846
