Tropical forests could soon lose their 'enchanted mist'

Global warming will deprive tropical mountain forests in Central and South America and the Caribbean of their iconic clouds.

cloud forest
Cloud forest in the Monteverde Cloud Forest Reserve, Costa Rica.Wikipedia

The gnarled and twisted trees in these tropical forests are cloaked in clouds and mist, much like the fairy tale forests drawn by British illustrator Arthur Rackham for the Brothers Grimm. But these are not the spectral woods traversed by Little Red Riding Hood or Hansel and Gretel. These are real. They attract curious visitors and sustain a rich diversity of life. Many are centuries old. Sadly, however, their most iconic feature — their foggy ethereal cloud cover — may vanish, another casualty of climate change.

arthur rackham comus
Arthur Rackham’s “Comus — The Lady enters,” 1921.Plum leaves

"These forests are a source of wonder," says Eileen Helmer, a scientist with the International Institute of Tropical Forestry, a program run by the U.S. Forest Service, and author of a new study in the journal PLOS ONE that describes the expected changes. "What makes them unique will disappear because of human-caused changes to the climate, which would be an unimaginable tragedy."

The research predicts that within the next 25 years, the wet, misty atmosphere that engulfs many tropical mountain forests in the Western Hemisphere could begin to evaporate, a victim of heat-trapping carbon pollution from burning of fossil fuels. It will simply become too warm to maintain them. “It takes more water to form cloud droplets in warmer air, and the bottom line is that the climate models predict warmer temperatures and less rainfall over land,” Helmer says.

Their loss will not only render these forests less beautiful, it will also hurt numerous species that live there. Millions of Monarch butterflies, for example, who spend their winters in the cloud forests of Central Mexico, count on the clouds to keep temperatures constant, and will almost certainly suffer from the increasing heat. The disappearing clouds also could endanger the Elfin Woods Warbler of El Yunque National Forest in Puerto Rico, and the Nightingale Thrushes who sing in Costa Rica’s Monteverde Cloud Forest Reserve.

monarch butterfly
A Monarch butterflyPixabay

“The reduced relative humidity will likely reduce the abundance of insects that the Elfin Woods Warbler feeds on,” Helmer says. “The other thing is that the warbler is likely in the habit of feeding on the range of insects found in these cooler, humid forests, and might have a hard time adapting to feed on other food sources. As for the Monarchs, studies have found that hot daytime temperatures may desiccate them, and nighttime frost is also a problem for them. Cloud clover modulates the temperature and humidity of the areas in Central Mexico where many Monarchs overwinter.”

Moreover, changing the nature of these forests also might prevent scientists from discovering as yet unknown species, she says. “Many of the species that are new to science in tropical countries are in cloud forests, including wildlife like bird and mammal species,” Helmer says. “So, there are probably many more undiscovered species in cloud forests that we might not ever learn about.”

Also, the mist is vital source of water in drier regions. Trees — and the plants and lichens that live on them — collect water from the vapor. The effects of climate change will impair this process as well, according to the study. “Water vapor condenses on cloud forest trees and the epiphytes [plants that grow harmlessly on other plants] on them, and this water eventually makes it way to streams,” Helmer says. “Without the cloud forests and the way that they capture water, these streams would have less flow.”

rosette plant
Large rosette plants in the páramo of Colombia.Friedrich Kircher

The epiphytic species that characterize cloud forests have very thin or finely divided leaves or other parts that are perfectly structured to capture water from the air, like very fine nets. “In the páramo [the high treeless plateau above the forests] many plants have ‘hairy’ leaves and stems that also scavenge water from the air,” she says.

In conducting their study, the researchers, which included scientists from the U.S. Forest Service labs in Puerto Rico and Fort Collins, Colorado, and from Colorado State University, charted current cloud forests and páramo by first mapping mountain size, relative humidity and frost frequency. "We then substituted future climate into the models we used to map current cloud forests, and compared the extent and relative humidity of cloud forests and páramo given different possible scenarios for climate change," Helmer says.

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Areas mapped by the study include Mesoamerica and the Caribbean islands (top) and South America (bottom).PLOS ONE

While the effects varied by region, the study found that virtually all cloud forests would experience loss. Only about 1 percent of all Western Hemisphere cloud forests — and these were only in a few South American locations — would see an increase in wet habitat.

“The most important step toward saving most cloud forest regions of the Western Hemisphere is to reduce greenhouse gas emissions to minimize climate change,” she said. “Even though we found that deforestation is a problem in more populated montane regions, particularly parts of the Andes, central Mexico and Mesoamerica and a few other places, most places with a cloud forest climate have at least some forest left, and forest covers most of these lands in many regions.

“Grazing and agriculture have altered vast areas of páramo lands, but we did not quantify this in the study,” she added. “Even for páramo, though, our study suggests that climate change, not human land uses, are the most important ecosystem risk.”

nightingale thrush
A Nightingale Thrush in Costa RicaMichael Woodruff

The major cloud forest areas expected to be least affected by climate change, which are in the Andes, tend to be the most deforested, she says. “This means that any remnant stands of old cloud forest in these places should probably be protected from any future deforestation, and that the areas surrounding these remnants should also be protected so that forests can regrow there. The remnant patches can serve as sources of dispersal of tree seeds and other plant and animal species.”

Finally, she says, “we should consider taking additional steps to preserve species in places where both deforestation and severe climate change effects are expected.” She added that local efforts to stem logging in central Mexico have helped preserve the cloud forest habitat for Monarchs.

Unfortunately, Helmer says, “without uniting to reduce greenhouse gas emissions from human activities, countless animal and plant species will likely be lost, including unique mammal and colorful bird and amphibian species that capture our imagination and enrich the human experience.”

Marlene Cimons writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art, and culture.