A study in Costa Rica shows that conserving tropical forests might increase yields of coffee, one of the world's most valuable export commodities. U.S. scientists found that coffee fields adjacent to forests had higher production than those farther away.

The economic value of maintaining tropical forests near farms might be much greater than previously thought. A team of U.S. researchers measured the output of 12 coffee fields on a big Costa Rican plantation and found that plots within one kilometer of a forest produced 20 percent more coffee than plots farther away. The quality of the yield was better, too, with 27 percent fewer small, misshapen beans.

The study leader, biologist Taylor Ricketts of the World Wildlife Fund, says the key to the improved harvest was increased pollination by bees from the nearby forest.

"Coffee does self-pollinate, but if you allow bees to visit and bring in cross pollen, it will yield better," he says.

Several studies from around the world have already shown this, but this new study in the Proceedings of the U.S. National Academy of Sciences is unique because it measured the economic value of bee pollination to the plantation. Mr. Ricketts' team used data on the farm's yield and market prices to show that just two coffee plots nearest the forest helped boost the farm's income significantly. They yielded $60,000 more a year in coffee, because of the pollination of bees from the nearby woodlands.

"So that if they were cut down or destroyed for any other reason, that farm could expect to earn about $60,000 less than they had been so far," Mr. Ricketts noted.

In fact, the study found that the value of tropical forests can be greater than other land uses for which they are often destroyed. The World Wildlife Fund says that cattle pasture, for example, would yield only about $24,000 a year, less than half of what pollination services provide the coffee plantation.

Mr. Ricketts calls the findings good news for conservationists and growers, who sometimes are at odds over land use.

"What this means is that the goals of conservation and economic development are in some cases more aligned than we thought," he explained. "Conserving natural systems can benefit the species that live there and also the human communities that live nearby them."

Cross-pollination from birds, bees and other insects is of value to more than just coffee. The United Nations Food and Agriculture Organization says two-thirds of the world's crops require it. But Mr. Ricketts and his colleagues point out that recent declines in wild and managed bee populations throughout the world have aroused concern, prompting the United Nations to create the International Pollinators Initiative. This is a program to coordinate scientific investigation on ways to conserve animal pollinators.