Guanacaste National Park includes large expanses of eroded pasture that once were covered with native dry forest, which at the time of the Spaniards’ colonization carpeted a greater area of Mesoamerica than did rainforests. It was also more vulnerable to encroaching civilization.

After 400 years of burning, only 2 percent of Central America’s dry forest remained. (Fires, set to clear pasture, often become free-running blazes that sweep across the landscape. If the fires can be quelled, trees can take root again.)

For four decades, American biologist Daniel Janzen has led an attempt to restore Costa Rica’s vanished dry forest to nearly 60,000 hectares of ranchland around a remnant 10,000-acre nucleus.

Janzen, a professor of ecology at the University of Pennsylvania, has spent six months of every year for more than 40 years studying the intricate relationships between animals and plants in Guanacaste Province.

A key to success is to nurture a conservation ethic among the surrounding communities. Education for grade-school children is viewed as part of the ongoing management of the park; all fourth-, fifth-, and sixth-grade children in the region get an intense course in basic biology. And many of the farmers who formerly ranched land are being retrained as park guards, research assistants, and guides.

Another 2,400-hectare project is centered on Lomas Barbudal Biological Reserve in southern Guanacaste. Lomas Barbudal is one of the few remaining Pacific coast forests favored by the endangered scarlet macaw, which has a penchant for the seeds of the sandbox tree (the Spanish found the seed’s hard casing perfect for storing sand, which was sprinkled on documents to absorb wet ink; hence its name).