Cloud forests dry up

Deforestation is drying out cloud forests

Published: Thursday 15 November 2001

costa Rica's lush mountaintops are losing their mist. "It drips," says ecologist Robert Lawton, describing the Costa Rican cloud forest, "and it's plastered with plants of all sizes climbing over each other. Stand still for long and they're growing on you." But the lush life he describes may be threatened. Satellite pictures show that deforestation at the foot of western Costa Rican mountains is drying out swirling summit mists.

The 7,358 square kilometres of forests at above 1,500 metres is sustained by the warm, wet tradewinds blowing off the Caribbean being forced upwards by the mountains where they cool and condense into a damp fog.

Where agriculture has eroded lowland forests, the fluffy cumulus clouds that feed the peaks' forests no longer form, Lawton, researcher at the University of Alabama in Huntsville, usa, reports along with colleagues. Water evaporating between the trees normally lowers the air temperature. In its absence, air is warmer and has to be lifted higher before it cools into mist.

"It's extremely worrying," says conservationist Philip Bubb, researcher at the uk-based Tropical Montane Cloud Forest Initiative. The findings may explain why the base of the cloud forest has begun to dry out, killing many species of frogs and toads. If lost, the forests would take more unique plants and animals with them. The peaks are isolated nests of biodiversity. "Specific species of orchids are found only on the mountaintops," says Bubb. Cloud forests also channel clean, fresh drinking water to people in towns below.

The larger fear is that the tropical cloud forests on the mountain ranges of Central and South America, Africa and Asia could be facing a similar fate. Trees are being cleared apace in these countries to make plantations and animal pasture. Most of lowland Costa Rica has already been cleared.

Lawton photographed cumulus clouds across Costa Rica and neighbouring Nicaragua using the Landsat and Geostationary Environmental Satellite. Atmospheric models confirm that clouds which form above a treeless landscape form at a greater height than those over forest.

Declining species and mist in the Costa Rican rainforest have previously been attributed to climate change warming air over the sea, explains Alan Pounds of the Monteverde Cloud Forest Preserve and Tropical Science Center in Costa Rica. Deforestation complements this idea, he thinks. Removing a buffer of trees may exacerbate the effect global warming is having.

The satellite findings show that conservation plans must now take into account the entire landscape: "You can't create a series of parks and expect biodiversity to be preserved," says Pounds.

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