Professor Maathai said the aggressive push for exotic tree species must be brought to an end, saying the imported species even became invasive in nature.

The founder of the Green Belt Movement said when the species turn invasive forest areas like those of Mt Kenya, Aberdare and Mau Complex are turned into grasslands, attracting large scale grazing.

"God had a reason to put some species where they belong. We need to focus on planting indigenous trees. They are best suited to regions where they are supposed to be," Prof. Maathai said.

Prof Maathai was giving a keynote address at the opening session of the 2nd World Congress on Agroforestry that kicked off Monday at the United Nations Environment Programme (UNEP) headquarter in Gigiri, Nairobi.

The five day workshop was also attended by among others the Director General of World Agroforestry Centre (ICRAF) Dr Dennis Garrity, UNEP Executive Director, Dr Achim Steiner and Agriculture Permanent Secretary, Dr Romano Kiome.

She said it was not right for policy makers to remain silent while trees like the eucalyptus which are imported from Australia and South Africa were causing havoc to the country's biodiversity.

"They are over promoted for commercial reasons. These trees are good for beauty but consume a lot of water when they are planted along rivers, wetlands and water shed areas," said Maathai .

The Nobel Prize cited Central Province where the growth of cash crops has been glorified at the expense of food crops.

"The diversity of food crops that guaranteed food security at homesteads where I grew up has diminished as the canopy of indigenous tree species which favors growth of food crops was replaced with exotic species," she said.

Prof. Maathai lauded steps taken by environment minister John Michuki who has banned eucalyptus growing along rivers and wetlands in the country.

She said four billion trees have been planted world wide since the Billion Tree Campaign was launched by UNEP four years ago. This she attributed to support extended by governmentsworldwide

Dr Steiner said Kenya requires at least 7 billion trees to be planted through nationwide tree campaigns by 2020 if the water towers in the country are to be restored.

"Trees are important to mitigate against climate change. As life support systems, they have been destroyed yet they are important as a means of livelihoods. This is happening at a time when the matter has taken a political debate," Dr Steiner said.

Dr Garrity said demand for timber, wood fuel and other tree products will keep on rising with the renewed global economic growth.

"The demand will have to be met largely from farm grown sources of tree products. Demand will far outstrip supply, prices will skyrocket, and all efforts to protect the remaining forests fail miserably," he said.

The conference comes at a time when the country is polarised over the debate on whether people who have settled on the water towers particularly the Mau forest should be evicted or not.

It also comes amid a severe water shortage that is facing the country compounded by a raging drought that has affected millions of Kenyans, all of which have largely been blamed on destruction of forests in the country.

Credit: Kenya Broadcasting Corporation

Enter your Pledge