When 61-year old Mercy Joshua was young, the vast forests of southeastern Kenya teemed with wildlife, but decades of unchecked deforestation by locals have devastated the land.

She watched forests dwindle and rivers dry up across her homeland of Kasigau -- a semi-arid savanna grassland dotted with shrubs, woodland and small rugged hills -- as people cut down the trees to scratch a living by selling them for firewood.

But now, after decades of degradation, a local project has found a way to preserve the forests and support the community by getting international companies to pay to plant trees.

"We were losing everything, but thanks to the project we have learnt even how to live with the wild animals," Joshua, a mother of four, told AFP.

"These days, we don't cut down trees... they are our friends," she added.

The project has breathed new life into Kasigau, a 500,000 acre (200,000 hectare) dryland forest 330 kilometres (205 miles) southeast of the capital Nairobi that connects the two halves of Kenya's renowned Tsavo national park.

Founded in 2009, it is part of a UN-backed carbon credit scheme aimed at stopping 54 million tonnes of carbon dioxide being released into the atmosphere over the next 30 years, equivalent to 1.2 million tonnes a year.

Leading buyers of the credits include Microsoft, Barclays Bank and Kenya Airways, which have invested $3.5 million (2.5 million euros) each since the project started.

These companies buy carbon credits by paying to conserve existing trees and plant new ones. The forests soak in carbon from the atmosphere, helping to reduce carbon dioxide levels in the air and so offset what the companies release themselves.

- 'No jobs, no water' -

The Kasigau scheme has also created a new source of income for impoverished local communities where most people scrape a living by hunting animals for meat or illegal charcoal production.

"There are no jobs here, no water, and I have a family to feed," said Matthew Mutie, a 40-year-old father of three who supports his family by making charcoal for around $3 a sack.

"Most of the people in this area are subsistence farmers and in most cases their crops fail due to poor rainfall," added Rob Dodson from Wildlife Works, which oversees the Kasigau project.

The scheme directly employs 400 people but also supports nearly 100,000 rural Kenyans in other projects, including sustainable charcoal production, tree nurseries, and eco-friendly craft products.

In a deeply poor region where many people live on $1 per day, the project has made a major impact, bringing in an average of $270 per person a year -- about a quarter of Kenya's GDP per capita.

"The project is a perfect example of how African countries can help in the fight against climate change, while at the same time benefitting the local communities," said Josep Gari, from the United Nations Development Programme.

Kenyan officials said the Kasigau project was helping to transform people's lives.

"Once an area is under a carbon credit scheme, the area becomes protected," said Elijah Mwandoe, a senior local government environment official.

"We tell communities if you have a tree standing, it is making our air clean, and if we have clean air then we will all benefit and we will get rainfall."

- 'Help society adapt' -

Deforestation accounts for roughly 15 percent of global greenhouse gas emissions every year, pumping more carbon dioxide into the atmosphere than the global transportation sector, according to Wildlife Works.

Global warming is already hitting southern Kenya. Tim Christophersen, from the UN Environment Programme (UNEP) said that climate change is "having an effect here on the local community... droughts are more frequent".

In response, UNEP is "also looking at large-scale restoration of forest in Kenya to help society here adapt," he said.

However, carbon credit schemes are not a panacea for global warming.

Some have been criticised for achieving little and being poorly policed, while a slowdown in global industrial production during the financial crisis has seen prices plummet.

But Gari insists that this project is generating wealth for the community, and so provides a more long-term bulwark against climate change.

The Kasigau team have succeeded in "accessing carbon markets in times of uncertainty and deflation for climate finance," he said.

It has also helped to improve the local forest habitat, which is home to some 500 elephants, as well as lions, cheetahs, zebras and more than 300 species of birds.

"The greatest success is that generally people now see the value to the environment," said Dodson of Wildlife Works.

"When we first came here we were shocked to see how rich the biodiversity of this area was and how poor the people were."