Once lush and abundant, the "green belt" surrounding Niger's capital of Niamey, created 50 years ago to try and halt the advance of the Sahara desert, is dying a slow death.

A rural exodus has taken its toll on Niger's greenest project, as populations left destitute by low crop yields move to the capital and cut down its trees to make ends meet.

"I have cut down dozens of these trees here," said Ali Moumouni, who lives in the downtrodden northern Niamey neighbourhood of Ouallam. "I sell the wood to survive."

A few metres (yards) away, men equipped with axes are clearing an area where they can build huts, under the watchful eye of their families. They have abandoned the countryside for the capital to try and earn some money.

"We have had a poor harvest this year so we have come to set up home here," explained Adamou Foumo, speaking in the local language, Djerma.

Land-locked Niger, one of the world's hottest and poorest nations, is already largely desert with a subsistence-based economy. The capital is located in a small fertile region in the south, where much of the country's 16 million population lives.

Niger's green belt took nearly 30 years to grow. Tree planting started in 1965, five years after the country proclaimed independence from France, and ended in 1993.

Funding for the 4.5 million-euro (6.2 million-dollar) project came mainly from abroad, said Niger's environment ministry.

"The idea was to make a wall of trees around the city to keep out the dust and stop the desert from advancing," a former project advisor who did not give his name told AFP.

"And the job was done. A green wall 25 kilometres (15 miles) long and one kilometre wide crosses Niger from east to west."

Man-made green belts are increasingly a subject of discussion in Africa amid concerns over desertification.

African leaders are pushing for the planting of a massive green belt, nicknamed the "Great Green Wall of Africa", which would cut right across the continent from Senegal in the west to Djibouti in the east, covering 7,775 kilometres (4,831 miles).

-- Growing Africa's 'lungs' --

The African great wall has the same aim as the Niamey green belt -- to hold back the mighty Sahara by planting drought-adapted species that would slow soil erosion and help rain water filter into the ground, effectively curbing the Sahara's spread south.

It would also aim to produce richer soil for local communities who rely on the land for agriculture and grazing.

But a lack of funding means the project has not yet gotten off the ground.

And while Niger's "green lung" did once breathe more freely, it is now in severe decline.

Almost half of its original 2,000-hectare (nearly 5,000-acre) surface area has disappeared.

"Things started to go wrong for the green belt when hundreds of rural people fled to the capital to escape the severe famine of 1984," remembered Hama Moussa, an ex-watchman at the belt site.

New neighbourhoods have started to spring up close to the area with names like "Iraq", "Kuwait" and "Little Paris" where hundreds of families live in straw huts or other makeshift shelter.

In 2008, some 2,000 squatters had their homes razed by bulldozers sent in by the authorities but nothing further was done.

"To survive, people just cut down the trees to make roofs and sell the rest in town," said Niamey resident Salifou Gourouza indignantly.

"With such excessive deforestation, the 'green belt' may disappear altogether," warned Abdoulaye Maizama, an official with the water and forests department.

A 2004 law that threatens anywhere from three months to two years' imprisonment for offenders has done little to discourage residents.

But it is not just Niamey's new arrivals -- petrol stations, car parks, fancy houses and mosques for Niger's predominantly Muslim population have all infiltrated the green belt.

There are other factors too, according to the private press which regularly accuses local authorities of selling plots of land in the green belt to rich businessmen, knowing that any building there is theoretically outlawed.

The belt has also become a sort of open-air wasteland, said Niamey's fire service, where blazes -- deliberate or accidental -- regularly ravage the zone.

Nevertheless Niger's government is trying to show it has not forgotten its green belt. On August 3 -- the anniversary of Niger's independence -- as every year, thousands of new trees were planted.