When he first visited the wind-swept Monteverde cloud forest in the 1970s, University of Alabama biologist Robert O. Lawton "fell in love." No wonder. It is a luxuriant patch of tropical forest tucked away in the Tilaran mountain range, a great green wall rising dramatically to 1,800 meters above the coastal lowlands of Costa Rica. Pilots recognize it by the permanent veil of cumulus clouds. Every year 70,000 tourists walk among the dripping forests, where relative humidity routinely reaches 100 percent, and marvel at the wealth of wildlife, from the ruby red-eyed tree frog to the sonorous blue-crowned motmot.
Tourists for the most part tread lightly on the delicate cloud-forest habitat. But the nature they seek in the highlands is facing a threat from afar. Developers, ranchers and small farmers have for decades been steadily slashing and burning their way deep into the lowlands of Costa Rica, near the coasts. Today only 1,200 square kilometers, or 18 percent of the original lowland forest, remains untouched. Nobody ever suspected that cutting forests at sea level would influence weather patterns on Tilaran, 30 miles downwind, but it does. As Lawton and colleagues wrote in last week's Science magazine, the results could prove disastrous for this aerie in the clouds and the rich nature it supports.
Scientists collected satellite images and field observations and then ran their data through a climate-change model from Colorado State University. Their initial findings are disturbing. As the trade winds pass over the now barren coastal forests, they pick up less moisture than they did when the forests were lush. When the hotter, drier air reaches the Tilaran mountains, it must climb higher before it yields enough moisture for clouds to form. Although the mountainside is still green, its life-giving mantle of clouds has been steadily shrinking.
Just what this means for the ecology of the Monteverde preserve is still an open question. A lot is at stake. The dense, dripping cloud forest regulates temperatures and contributes to rainfall in the surrounding tropics. Its leafy canopy is home to an empire of animals and microorganisms, and more epiphytes--plants that live off other plants--than anywhere else on earth. Scientists are especially concerned over the fate of many cloud-forest birds, such as the resplendent quetzal, with its streaming tail feather, and the three-wattled bellbird, so named for its patented clanging call. Botanists have also cataloged 475 species of orchids.
Environmental scientists first suspected something amiss in the late 1970s, when they observed a change in the habits of Monteverde wildlife. As clouds receded, birds and bats were forced to fly ever higher up the slopes. Scientists suspect that some reptiles have fled their old habitats altogether, leading to a general collapse of the reptile population. The splendid golden toad (Bufo periglenes), named after the male's bright gilded hue, has been declared extinct; it was unique to Monteverde. "Lose a cloud forest and you lose a whole family of species, some of which may be unique," says Lawton.
It's not too late, he says, to restore the clouds. Slowing deforestation along the coasts and replanting cleared areas with fruit trees could help restore moisture to the air. It will take years of work before scientists know just how severe the damage will be to Monteverde. But by then, many more species may have gone by the wayside.