Severe drought in the 1970s and 80’s, coupled with a population explosion and destructive farming and livestock practices, was denuding vast swaths of land. The desert seemed determined to swallow everything. So Mr. Danjimo and other farmers in Guidan Bakoye，the Sahel, a semiarid belt that spans Africa just below the Sahara took a small but radical step. No longer would they clear the saplings from their fields before planting, as they had for generations. Instead they would protect and nurture them, carefully plowing around them when sowing millet, sorghum, peanuts and beans.
Today, the success in growing new trees suggests that the harm to much of the Sahel may not have been permanent, but a temporary loss of fertility. The evidence, scientists say, demonstrates how relatively small changes in human behavior can transform the regional ecology, restoring its biodiversity and productivity.
In Niger’s case, farmers began protecting trees just as rainfall levels began to rise again after the droughts in the 1970s and 80’s.
Another change was the way trees were regarded by law. From colonial times, all trees in Niger had been regarded as the property of the state, which gave farmers little incentive to protect them. Trees were chopped for firewood or construction without regard to the environmental costs. Government foresters were supposed to make sure the trees were properly managed, but there were not enough of them to police a country nearly twice the size of Texas.
But over time, farmers began to regard the trees in their fields as their property, and in recent years the government has recognized the benefits of that outlook by allowing individuals to own trees. Farmers make money from the trees by selling branches, pods, fruit and bark. Because those sales are more lucrative over time than simply chopping down the tree for firewood, the farmers preserve them.
The greening began in the mid-1980s, Dr. Reij said, “and every time we went back to Niger, the scale increased.”
“The density is so spectacular.” he said.
Mahamane Larwanou, a forestry expert at the University of Niamey in Niger’s capital, said the regrowth of trees had transformed rural life in Niger.
“The benefits are so many it is really astonishing,” Dr. Larwanou said. “The farmers can sell the branches for money. They can feed the pods as fodder to their animals. They can sell or eat the leaves. They can sell and eat the fruits. Trees are so valuable to farmers, so they protect them.”
They also have extraordinary ecological benefits. Their roots fix the soil in place, preventing it from being carried off with the fierce Sahelian winds and preserving arable land. The roots also help hold water in the ground, rather than letting it run off across rocky, barren fields into gullies where it floods villages and destroys crops.
One tree in particular, the Faidherbia albida, known locally as the gao tree, is particularly essential. It is a nitrogen-fixing tree, which helps fertilize the soil.
Its leaves fall off during the rainy season, which means it does not compete with crops for water, sun or nutrients during the growing period. The leaves themselves become organic fertilizer when they fall.
47. The word “arable” in the third paragraph from the bottom can be substituted by（ ）.
48. The denuding of vast swaths of land was not caused by（ ）.
49. A small change in human behavior can（ ）.
50. Today the law has changed to（ ）.
51. The benefits of trees to farmers does not include（ ）.
52.（ ）is not an ecological benefit of the trees in rural Niger.
