NAIROBI, Kenya (AP) -- Kenya's former president called her a mad woman. Seen as a threat to the rich and powerful, Wangari Maathai was beaten, arrested and vilified for the simple act of planting a tree, a natural wonder Maathai believed could reduce poverty and conflict.

Former elementary students who planted saplings alongside her, world leaders charmed by her message and African visionaries on Monday remembered a woman some called the Tree Mother of Africa. Maathai, Africa's first female winner of the Nobel Peace Prize, died late Sunday in a Nairobi hospital following a battle with cancer. She was 71.

Maathai believed that a healthy environment helped improve lives by providing clean water and firewood for cooking, thereby decreasing conflict. The Kenyan organization she founded planted 30 million trees in hopes of improving the chances for peace, a triumph for nature that inspired the U.N. to launch a worldwide campaign that resulted in 11 billion trees planted.

Maathai, a university professor with a warm smile and college degrees from the United States, staged popular protests that bedeviled former President Daniel arap Moi, a repressive and autocratic ruler who called her "a mad woman" who was a threat to the security of Kenya.

In the summer of 1998, the Kenyan government was giving land to political allies in a protected forest on Nairobi's outskirts. Maathai began a campaign to reclaim the land, culminating in a confrontation with 200 hired thugs armed with machetes and bows and arrows. When Maathai tried to plant a tree, she and her cohorts were attacked with whips, clubs and stones. Maathai received a bloody gash on her head.

"Many said, 'She is just planting trees.' But that was important, not only from an environmental perspective, to stop the desert from spreading, but also as a way to activate women and fight the Daniel arap Moi regime," said Geir Lundestad, director of the Nobel Institute, which awarded Maathai the peace prize in 2004.

"Wangari Maathai combined the protection of the environment, with the struggle for women's rights and fight for democracy," he said.

Maathai said during her 2004 Peace Prize acceptance speech that the inspiration for her life's work came from her childhood experiences in rural Kenya. There she witnessed forests being cleared and replaced by commercial plantations, which destroyed biodiversity and the capacity of forests to conserve water.

After arap Moi left government, Maathai served as an assistant minister for the environment and natural resources ministry.

Although the tree-planting campaign launched by her group, the Green Belt Movement, did not initially address the issues of peace and democracy, Maathai said it became clear over time that responsible governance of the environment was not possible without democracy.

"Therefore, the tree became a symbol for the democratic struggle in Kenya. Citizens were mobilized to challenge widespread abuses of power, corruption and environmental mismanagement," Maathai said.

Maathai's work was quickly recognized by groups and governments the world over, winning awards, accolades and partnerships with powerful organizations. Meanwhile, her dedication to nature remained, as could be seen in her role in a movie called "Dirt! The Movie," where Maathai narrated the story of a hummingbird carrying one drop of water at a time to fight a forest fire, even as animals like the elephant asked why the hummingbird was wasting his energy.

"It turns to them and tells them, 'I'm doing the best I can.' And that to me is what all of us should do. We should always feel like a hummingbird," she said. "I certainly don't want to be like the animals watching as the planet goes down the drain. I will be a hummingbird. I will do the best I can."

Recognizing that never-say-die attitude, Kenyan Prime Minister Raila Odinga said Maathai's death "strikes at the core of our nation's heart." Odinga said Maathai died just as the causes she fought for were getting the attention they deserve.

The United Nations Environment Program called Maathai one of Africa's foremost environmental campaigners and recalled that Maathai was the inspiration behind UNEP's 2006 Billion Tree Campaign. More than 11 billion trees have been planted so far.

"Wangari Maathai was a force of nature. While others deployed their power and life force to damage, degrade and extract short term profit from the environment, she used hers to stand in their way, mobilize communities and to argue for conservation and sustainable development over destruction," said Achim Steiner, the executive director of UNEP.

Tributes poured out for Maathai online, including from Kenyans who remember planting trees alongside her as schoolchildren. One popular Twitter posting noted that Maathai's knees always seemed to be dirty from showing VIPs how to plant trees. Another poster, noting Nairobi's cloudy skies Monday, said: "No wonder the sun is not shining today."

Her quest to see fewer trees felled and more planted saw her face off against Kenya's powerful elite. At least three times during her activist years she was physically attacked, including being clubbed unconscious by police during a hunger strike in 1992.

Archbishop Desmond Tutu on Monday called Maathai a "true African heroine." The Nelson Mandela Foundation also expressed sadness. The foundation hosted Maathai in 2005, when she headlined the foundation's annual lecture.

"We need people who love Africa so much that they want to protect her from destructive processes," she said in her address. "There are simple actions we can take. Start by planting 10 trees we each need to absorb the carbon dioxide we exhale."

The spokesman for U.N. Secretary-General Ban Ki-moon said Maathai was a "pioneer in articulating the links between human rights, poverty, environmental protection and security."

A long time friend and fellow professor at the University of Nairobi, Vertistine Mbaya said that Maathai showed the world how important it is to have and demonstrate courage.

"The values she had for justice and civil liberties and what she believed were the obligations of civil society and government," Mbaya said. "She also demonstrated the importance of recognizing the contributions that women can make and allowing them the open space to do so."

Njeri Gatonyo, a member of the Green Belt Movement board, said Maathai's organization will continue with the work that Maathai began in 1977. Mbaya said work would continue to establish a Wangari Maathai Institute for Environmental Studies and Peace at the University of Nairobi.

Maathai was the first woman to earn a doctorate in East Africa - in 1971 from the University of Nairobi, where she later was an associate professor in the department of veterinary anatomy. She previously earned degrees from Mount St. Scholastica College - now Benedictine College - in Atchison, Kansas and the University of Pittsburgh.

The Green Belt Movement said on its website that Maathai's death was a great loss to those who "admired her determination to make the world a more peaceful, healthier and better place." Edward Wageni, the group's deputy executive director, said Maathai died in a Nairobi hospital late Sunday. Maathai had been in and out of the hospital since the beginning of the year, he said.

Maathai is survived by three children. Funeral arrangements were to be announced soon, the Green Belt Movement said.

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Associated Press writer Malin Rising in Stockholm, Sweden contributed to this report.

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Online:

http://greenbeltmovement.org

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