Interview with Robert Lawton: Scientists Find Clear Skies Mean Mayhem for Cloud Forest Species

Robert Lawton did not set out to show a disquieting relationship among deforestation, the weather, and ecosystems in Costa Rica. A professor of biology and a tropical forest botanist at the University of Alabama at Huntsville, he originally wanted to quantify the extent of cloud cover in the Monteverde Cloud Forest Reserve in Costa Rica, where he has done fieldwork for some 30 years.

Illustration by Allan Núñez ('Nano')
Lawton’s university colleague Ron Welch, chairman of the Department of Atmospheric Sciences, had developed a technique for establishing the altitude of cumulus cloud bottoms, based on satellite photos that show the cloud shadows. So in 1999, Lawton and Welch began studying satellite photos of areas upwind of Monteverde, where there should be masses of the fluffy clouds gathering together and filling with water. The area should be a cumulus incubator, generating the clouds that envelope Monteverde’s hills. But to the scientists’ surprise, the photos showed few clouds.

While the satellite images showed lots of cumulus clouds in Nicaragua, just to the north, and plenty near Tortuguero National Park on the Caribbean coast, there was little cloud development over the lowlands northeast of Monteverde, a cool and misty tourism hotspot. At first, Lawton and Welch figured the photos must be incorrect. But the next group of photos, and subsequent groups, showed the same generally cloudless skies. And in the manner of scientists who have stumbled upon something new and interesting, they thought — as Lawton reports — “Hey, maybe it’s a pattern.”

And so a new study was launched, with modest funding from NASA. Lawton explains what happened next: “One of the most obvious explanations was that the areas where the photos were taken are deforested. We started thinking about whether deforestation would have this kind of impact, and if so, why. Ron Welch had a graduate student, Udaysankar Nair, who has since earned his Ph.D., who modeled the process, using mathematical modeling schemes. The models corroborated what we saw on the satellite photos, predicting that the deforested areas should have poor cumulus cloud cover.

“This made sense. Typically, croplands and grasslands reflect more of the solar energy that impinges on them than do forested lands. Typically, croplands and grasslands have shallower rooting. Typically, more of the rainfall that hits them runs off as stream flow, so less stays in the local system. The shallower rooting, more runoff, and less water mean that grasslands transpire less — they evaporate less water. Since they are using less energy in the evaporation of water, they are often physically, tangibly hotter than forested land, and they transfer more energy as this sensible heat by conduction and convection into the atmosphere.

“So energy budgets are typically different between grasslands and forest. Forests put more water into the atmosphere and transfer less heat through conduction and convection. Other things being equal, you would expect these conditions to result in a cooler, moister atmosphere over forests and warmer, dryer atmosphere over grasslands. That should mean cloud formation is more likely over forests than grasslands.”

As you might expect, “cloud forests” are nearly always enveloped in mist and low-hanging clouds. Scores of plant and animal species are found in cloud forests and nowhere else. Naturally, if the atmosphere changes — if there are fewer clouds, warmer air, and less moisture — the shift will have an impact on cloud forest flora and fauna.

In Monteverde, biologists were puzzled by the 1989 disappearance of the golden toad. Since the tiny, brightly colored amphibian suddenly vanished, studies done by Alan Pounds, Michael Fogden, and John Campbell have tracked population crashes for other amphibian species. Their research points to unprecedented shifts in the climate — likely related to global warming — that have caused the cloudbank in Costa Rica’s highlands to lift, changing the ecosystem and apparently affecting sensitive species like the golden toad.

But the University of Alabama team’s study is the first to point to deforestation’s role in the change of weather and the ecosystem in Monteverde. The implications are troublesome, as Lawton reports:

“From our point of view, there are a number of reasons to worry about the cloudiness of montane forests. One involves just the conservation implications. These cloud forests are communities of organisms adapted to cloud forest conditions. Take away the cloudy conditions, and we might expect to see all sorts of changes, such as Alan Pounds is documenting. How many cloud forest organisms could go the way of the golden toad?

“The other interesting problem is that cloud forests are such important components of many montane watersheds that provide either potable water supplies or the water for hydroelectric facilities. Monteverde’s forests feed the Lake Arenal hydroelectric project. So one of the serious questions is to what extent cloud input is important to the water budgets of watersheds like Arenal. If it is really important, then there are big economic reasons — in addition to conservation reasons — to care about cloud forests.”

To help answer these questions, Lawton and his colleagues will be working with Dutch, U.S. and Costa Rican scientists in Monteverde to see if deforestation has an impact on cloud forest water yield. This research is part of a coordinated effort involving a three-year, $480,000 NASA-supported follow-up study, and a British Department for International Development-supported study of cloud moisture inputs to forest and pasture watersheds in the mountains. The scientists will also conduct a flora and fauna inventory in both the cloud forests on the windward side of the country’s central mountain range and in small areas on the leeward side that routinely receive moisture from clouds rolling over the hilltops. They will also study whether deforestation on the country’s Pacific coast influences how clouds hit the Caribbean slope.

If the impacts of deforestation are as serious as the scientists’ research indicates, what can be done? Would reforestation be a solution? Possibly, Lawton says, but planting trees on the entire Caribbean slope would not be economically or socially feasible. He continues:

“An interesting question is: What kinds of land-use changes would give us some of the benefits of complete forest cover? Perhaps we could replace grasslands with orchard crops. Where grasslands exist, we could reforest along creeks, breaking up the pasture landscape. We need to know at what point adding trees in socially and economically acceptable ways returns enough water to the atmosphere to have an impact.

“These are all interesting questions for consideration in Nicaragua and eastern Honduras, which are still largely forested. We need to consider that development and deforestation can have major consequences on off-site ecosystems.”


Robert Lawton
Department of Biological Sciences
University of Alabama
Huntsville, AL 35899, USA
Tel: 256/824-6388
Fax: 256/824-6305

Read more about this project in the Eco-Index:


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