Misty No More?

The clouds over the Monteverde cloud forests of Costa Rica are shrinking—and sitting higher above the mountain peaks—as a result of deforestation in the lowlands, according to a study in the October 19 issue of the journal Science.Robert Lawton, a forest ecologist at the University of Alabama in Huntsville, and his colleagues conducted the research.

Enveloped almost continuously by fog and mist, cloud forests are hotbeds of biodiversity, harboring innumerable plants and animals that are found nowhere else in the world.

In many regions, cloud forests are also a critical year-round source of clean water for people living in the surrounding lowlands.

But cloud forests are high on the list of the world’s endangered ecosystems, Lawton and his colleagues warn.

“Cloud forests are very wet and very rainy, and people didn’t want to live there—you couldn’t grow corn and beans there, for instance,” Lawton said. “But increasing population pressure has forced people to slowly encroach on areas once considered uninhabitable.”

“The most direct threats to cloud forests are land being cleared for farming,” agrees Philip Bubb, a cloud-forest specialist with the World Conservation Monitoring Center and the United Nations Environment Programme. “In some cases, farm land erodes, so farmers move farther up the mountain.”

In other regions, he added, mining and oil exploration, cattle ranching, and logging are threats.

Global climate change also could be a problem, said Bubb. A study two years ago in Nature, he pointed out, indicated that there may be a link between rising sea temperatures and clouds forming above the mountain tops, causing the forests to dry out.

Conservationists have been working to protect cloud-forest areas by establishing nature reserves. The findings of the new study suggest that this strategy is not enough to halt the loss.

“Conservation biologists in Monteverde have been quite happy and proud of what they’ve been able to protect, land that extends virtually all the way down the Pacific slope,” said Lawton. “So it comes as a surprise to learn that the forests might be imperiled by what happens 100 kilometers (60 miles) downwind.”

Remarkable Diversity

The Monteverde cloud forest in Costa Rica straddles the Continental Divide, flowing down toward both the Pacific and the Caribbean coastlines.

On the Caribbean side, the cloud forest begins at an elevation of about 4,430 feet (1,350 meters). It peaks at the top of the Tilaran Mountains at around 6,070 feet (1,850 meters) and then flows down the Pacific slope to around 4,920 feet (1,500 meters).

Trees at the lower elevations grow to form a forest canopy 115 feet (30 to 40 meters) high. Closer to the top, tree are stunted by the impact of constant winds. They grow to heights of 16 to 33 feet (5 to 10 meters), forming an elfin forest.

Monteverde harbors at least 878 species of epiphytes (plants that grow on other plants), including 450 kinds of orchids. Trees are covered with mosses, bromeliads, and ferns.

There are more than 425 species of birds, 5,000 species of moths, and innumerable other plants and animals, including jaguars, tapirs, and pumas, and exotic species such as resplendent quetzals and three-wattled bellbirds.

“Everyone should visit a cloud forest,” said Lawton. “They’re truly spectacular.”

Costa Rica’s cloud forests have shown signs of environmental stress over the past decade. Amphibian populations have declined drastically and the range of certain bird populations has shifted.

Deforestation and Cloud Cover

The Monteverde cloud forests form when the trade winds that blow over the Caribbean reach land, Lawton explained. “Clouds form as the air rising over the mountains cools to the point where water condenses,” he said.

The amount of moisture and heat that is transferred from the surface to the atmosphere determines how many clouds are formed and how high they are suspended atop the mountains.

When the trade winds travel over forested land, the exchange of heat and moisture creates the right conditions for keeping the upper ranges of the mountains enveloped in clouds. But the lowland forests of Costa Rica are being steadily eroded by deforestation.

Clearing forests for farming and grazing land decreases the amount of available moisture and increases the amount of heat that’s sent into the atmosphere. This, in turn, diminishes cloud formation—fewer clouds are formed, and they sit at higher levels.

“This study,” said Bubb, “provides evidence for what has been conjecture, which is very worrying, because many cloud forests around the world are subject to deforestation in the lowlands.”

Satellite imaging confirmed visual evidence that, compared with forested areas, deforested lowlands that lay upwind of Monteverde had few or no cumulus clouds or clouds that were poorly developed. Moreover, clouds that formed above pasture lands were based at higher levels than those above tropical forests.

“The health of a cloud forest depends on it remaining wet, and our simulations show that the cloud cover over Monteverde is being reduced,” said Lawton.

“We’re losing a lot of rare habitat,” he added. “Each cloud forest is distinct, and forests separated even from one mountain peak to another have completely different sets of species.”

Lawton and his colleagues hope to focus future research on possible ways to remedy the situation.

“If deforestation is having these consequences, then it stands to reason that something like reforestation would ameliorate the problem,” said Lawton.

Atmospheric and mathematical modeling, Lawton suggested, might be helpful to show whether water and heat transfer could be improved by planting alternative kinds of crops—say, citrus plants instead of avocado orchards or sugar cane versus manioc.

“The lesson for conservationists here is that it’s not enough to protect just the mountain forests,” said Bubb. “You need a whole landscape plan that includes the lowlands. We need to form biological corridors and maintain existing ones.”

By Hillary Mayell
for National Geographic News
October 19, 2001