The BBC's Michael Peschardt reporting from Australia

The BBC's correspondent in Australia, Michael Peschardt, says widespread deforestation has caused the water table to rise, lifting thousands of tons of salt into the top soil.

Nothing can grow in the resulting desert.

Since white settlement of Australia started in the 18th century an estimated 15 billion trees have been cut down to make way for farms or urban development.

The trees held the rising water levels in check, their roots sucking up millions of gallons of water which then evaporated in the hot sun.

When the trees are felled the water table rises and the top soil becomes salty.

'Trees must be planted'

Land may never recover

The council says only a massive tree replanting programme can reverse the process because agricultural crops do not suck up enough water.

But farmers are still felling trees. Every year hundreds of acres lose their protection against the saline menace lurking beneath the surface.

A spokesman for the Australian Science Council, Dr Peter Cullen, says: "I do not know whether we are going to be able to hold it or not. It is one of the most difficult natural resource problems we are facing."

The scientists say unless something is done a third of the Australian continent could become a sterile white desert within 100 years.

The worst affected areas are around Perth, in western Australia, and in south eastern Australia.