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."
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