Greedy farmers, hungry goats and uncontrolled fires threaten to turn the Mediterranean coast and the farmlands of Spain into desert, according to a leading environmentalist.

A full quarter of Spain, including the Costa del Sol and the hinterland, a tourist paradise which includes some of the country's richest fruit and vegetable land, is in danger, according to the head of the government environmental agency."Twelve million hectares (30 million acres), or one-fourth of the country, are affected by severe erosion that could turn them into a desert unless it is checked," said Santiago Marraco, director of the Institute for Preservation of Nature (ICONA).

He said half of Spain was in a fragile equilibrium, and only one quarter was unaffected.

A highly placed government official, who declined to be named, said desertification was one of the worst long-term problems facing the country and its lucrative agriculture.

Marraco dismissed speculation that desertification could be linked to spectacular changes in weather patterns.

"This is not the Sahara desert moving north," he said.

He pointed at more trivial culprits -- greedy peasants overfarming, goats grazing the land barren, careless tourists starting forest fires. All were contributing to deforestation, the main cause of erosion that turns fertile soil into sand and stones.

Once upon a time, the legend goes, squirrels hopped across the country from tree to tree without ever touching the ground.

Now travelers in many parts of central and southern Spain marvel at vast horizons of bush and yellowing grass where few trees offer shelter from the burning sun.

Unlike central and northern Europe's tall trees, the most common trees in Spain are small oaks, which bring little income to their owners. Farmers started burning them down many centuries ago for charcoal or to make way for pastures.

"They believed that what they burnt down was worthless," Marraco said.

But unknowingly, they rid their land of its protective cover, making it prey to violent Mediterranean downpours that wash away the soil.

Without the oaks, the land can support only more simple trees, such as pines. When the pines are burnt down, the land can only support bush. If the bush is burnt or grazed by goats, it turns into short grass, Marraco explained. The next stage is a barren landscape of sand and stones.

To grow oaks again, one has to go back through each stage.

"It takes 400 years," Marraco said.