Maathai founded a campaign that has planted 30 million trees across Africa in a bid to slow deforestation.

"Activities that devastate the environment and societies continue unabated," Maathai, Kenya's deputy environment minister, said in a Nobel acceptance speech at a glittering ceremony in Oslo City Hall.

"Today we are faced with a challenge that calls for a shift in our thinking, so that humanity stops threatening its life-support system," Maathai, 64, told an audience of about 1,000 people including Norway's King Harald and Queen Sonja.

"I call on leaders, especially in Africa, to expand democratic space and build fair and just societies," she said.

"Further, industry and global institutions must appreciate that ensuring economic justice, equity and ecological integrity are of greater value than profits at any cost," she said. She said grassroots citizens' movements should be encouraged.

Maathai collected a gold Nobel medal and a diploma to a standing ovation. She separately receives a check for 10 million Swedish crowns ($1.48 million).

The Nobel Prizes were set up in the 1895 will of Swedish philanthropist Alfred Nobel, 10 years before Norway won independence from Sweden.

HEAL THE EARTH

Maathai will use the cash to expand her Green Belt Movement around the world.

"We are called to assist the Earth to heal her wounds and in the process heal our own," she said.

Her tree-planting movement, led mostly by women, aims to produce firewood, building materials and to slow deforestation. Kenya has lost about 90 percent of its forests in the past 50 years.

The movement also works for women's rights, democracy and peace.

Maathai said a stream where she used to see frogs and tadpoles as a child 50 years ago had dried up. "The challenge is to restore the home of the tadpoles and give back to our children a world of beauty and wonder," she said.

Maathai dismissed critics who say environmentalism has too little to do with peace to warrant the Nobel accolade.

"The state of any country's environment is a reflection of the kind of governance in place, and without good governance there can be no peace," she said.

"This year, the Norwegian Nobel Committee has evidently broadened its definition of peace still further," said committee chairman Ole Danbolt Mjoes, noting past prizes to politicians, anti-communist dissidents or human rights workers.

In an interview with Reuters, Maathai brushed aside her past suggestions that the deadly AIDS virus might have been the result of a laboratory experiment gone awry.

"I really don't know. I really don't have any idea. I'm not an expert in this field," she said. She also denied suggesting that scientists might have created the virus as a biological weapon against Africans.