Forest loss leads to local climate change effect in Borneo

Segama River seen from the view point platform at the Borneo Rainforest Lodge, Danum Valley, Sabah, Malaysia. CIFOR/Greg Girard
Monica Evans
25 April 2018

BONN, Germany (Landscape News) — If you have ever perspired under the sun in the tropics and then experienced the welcome crispness of the shade offered by the leafy boughs of a tree, the focus of a new study by scientists at the University of Queensland and the Norwegian University of Life Sciences clearly linking forest loss and local climate change in Borneo seems obvious: forests help keep things cool.

But until now, very little research has been undertaken at regional scales to back that up, says scientist Douglas Sheil, who is a co-author of the study and a senior associate at the Center for International Forestry Research (CIFOR).

The impact of deforestation on ecosystem services and biodiversity is well-documented, but its effect on local climate is much less widely known. In many parts of the world, forest loss may be just as influential as the warming effects of greenhouse gases in terms of its impact on climate.

“This is a big part of the climate change equation that’s really not been fully understood or addressed,” Sheil said. “We seem to talk about carbon all the time, and of course that’s important, but it’s far from being the whole story.”

Forests have been termed the “air conditioners” of the landscape, because they keep things cool by evaporating water. “If that evaporation effect is not there, a lot of the energy that’s coming from the sun goes into raising temperatures instead,” Sheil added.

The evaporated water forms clouds, which also contribute to cooling.

“It’s like a parasol that reflects a lot of the radiation of the sun back into space,” Sheil said – and is a source of rainfall. So when tropical forests are felled, local temperatures tend to rise, and rainfall patterns change, becoming less reliable and more extreme.

CLEAR CORRELATIONS

The Southeast Asian island of Borneo provided the researchers with something of a bittersweet blessing: an uncommonly good-quality set of historical data on local land cover change, daily temperatures and rainfall patterns, telling part of the story of an island that has experienced severe forest loss over recent decades.

Sheil, who has spent a lot of time on the island over the years, said it is a land that’s close to his heart. “It’s a very special place,” he said.

“Biologically, it’s probably one of the richest ecosystems on the planet, vast numbers of species, of plants and animals, really lush forests: the textbook image of what a tropical rainforest should be like.”

The island also claims the dubious honor of being one of the world’s “deforestation hotspots.” In the 1930s, around 75 percent of Borneo was covered in tropical forest; now, less than half of that remains. Drivers of deforestation on the island include global demand for timber, palm oil and rubber, an increase in smallholder agriculture and a series of forest fires.

Oil palm and timber plantations now cover at least 10 percent of the island. From the mid-1970s to the 1990s, more than half of all tropical hardwood exports worldwide came from Borneo. The island’s peat swamp forests have been drained extensively to make way for plantations, which increases their susceptibility to fire.

The researchers found a strong relationship between deforestation and mean monthly temperature increase, as well as more frequent hot temperature extremes. They found that the changes in climate were extremely localized, with clear variation in temperature between forested and deforested parts of the island: on average, in Borneo’s lowlands, deforested areas were warmer by 1.7 degrees Celsius than those with forests still intact.

The study also showed a particularly significant relationship between forest loss and rainfall reduction, with watersheds characterized by more than 15 percent forest loss experiencing rainfall reduction of more than 15 percent.

These trends were consistent across multiple sites around the whole island. While perhaps not surprising at the intuitive level, it’s “quite special” to have the data to demonstrate these relationships regionally, Sheil said.

“I think this is probably about the clearest correlation pattern seen from the tropics anywhere.”

ETHICS OF PRESERVATION

So what might this all mean for Borneo? According to lead author of the study Clive McAlpine of Australia’s University of Queensland, the research “really highlights the critical role of forests in regulating the island’s climate.”

If deforestation on the island continues, greenhouse gas emissions are cause for concern at wider scales. Locally, as the research has shown, climate impact is likely to have “far reaching impacts on the environment, agricultural productivity and human livelihoods in Borneo in coming decades,” McAlpine said. Furthermore, the previously rare combination of conditions that cause tropical rainforests to catch fire may become more common.

“It looks like a pretty grim picture at the moment,” acknowledged Sheil.

There is hope for halting and reversing the trend, he said, although the ethics of doing so need to be carefully considered.

“We tend to oversimplify and say it’s oil palm, or whatever, but if it wasn’t oil palm, the people living there would still want to make money somehow, and they’d still be looking to their land to create those opportunities,” he says.

“So if we want to protect the forest, we need to think about how we’re willing to pay for it.”

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