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The impacts of haze on Southeast Asia’s wildlife

  • Authorities and researchers are still shockingly ignorant of the ecological impacts of the smoke from Indonesia’s annual fires.
  • Some creatures are likely finding it harder to sing, which is often crucial for attracting mates, defending territory and more.
  • An orangutan disease called airsacculitis might be more prevalent during the smoky season.

For several months until very recently, a gray pall of haze hung over Singapore, a result of uncontrolled wildfires and peatland hotspots in neighboring Indonesia. And as Anuj Jain from the National University of Singapore (NUS) conducted his research on tropical butterfly conservation in the city state’s forests and parks, he noticed something wrong: less of the insects were fluttering around. In addition, animal activity as a whole had dropped markedly.

Jain was not alone in his observations. Singapore’s captive birds were singing less, and researchers in a rooftop garden study observed lower bird activity on smoky days. But besides these superficial observations nobody could be truly sure how living organisms and the larger ecosystem were being affected by the toxic haze.

Smog from Indonesian wildfires has regularly blanketed Southeast Asia for decades, with particularly bad recent episodes in 1997, 2006 and 2013. This year’s event seems to have finally concluded with the recent rains, but it could be the worst in history, with Indonesia alone reporting a death toll of 19 and 500,000 citizens suffering from respiratory ailments. However, despite this (largely manmade) disaster’s long history and consistency, authorities and researchers are still shockingly ignorant of the ecological costs to one of the world’s richest regions of biodiversity.

The impacts of the fires that cause the haze are much clearer in comparison. Raging flames destroy vast tracts of rainforest, incinerating seedlings and saplings and wiping out seed viability in the soil seed bank. Living organisms unfortunate enough to be caught in the blaze are asphyxiated or burned to death. Many of those that survive die from starvation, habitat destruction or are killed when they flee into human settlements. But deeper ecological insights hardly extend to the toxic haze that is born from the flames.

Fires at the peatland in the district of Kapuas in the Central Kalimantan province on Borneo island, Indonesia. Peatland soils store a massive amount of carbon. When peatlands are cleared and drained for plantations, they degrade and the carbon they store starts to release into the atmosphere as CO2 emissions. If peat soils catch fire, they can smoulder away below the soil surface, which is exceedingly difficult to extinguish.
A peatland fires rages in Central Kalimantan, Indonesia.

Take animal reproduction. During the 2006 haze, researchers in Indonesian Borneo, or Kalimantan, recorded a marked decrease in frequency and duration of Bornean white-bearded gibbon (Hylobates albibarbis) song. The researchers suggested respiratory problems as the likely cause. Knowing how fundamental singing is to territorial defense, communication and pair bonding, they postulated that reduced singing for extended periods could affect reproduction.

That was similar to the lower levels of birdsong noticed in Singapore this year, with Natalia Huang writing in national broadsheet The Straits Times that the smoky air would affect birds’ abilities to attract and find mates. Huang, an ecologist at environmental consultancy Ecology Matters, added that amphibians, with their permeable skins and need for moisture, could be likewise less able to locate mates in hazy conditions.

However, it isn’t known for certain. And nobody seems to have yet conducted research on the links between the haze and animal reproduction.

Frogs mate in the Malaysian state of Sabah. Photo by Rhett A. Butler
Frogs mate in the Malaysian state of Sabah. Photo by Rhett A. Butler

When it comes to plants, researchers are slightly more knowledgeable. By settling on leaves and reducing the strength of the sun’s rays, the particulates and chemicals in the haze affect plants’ reproductive and photosynthesis capabilities. Smoky conditions also reduce the ability of insects to pollinate flowers.

Huang writes that the carbon-based particles in the haze could dissolve into rainwater and lead to acid rain, which could fatally affect plant functions and damage entire ecosystems. But how exactly haze affects a habitat becomes less clear the larger the scope, and normal ecological studies on ecosystem-wide scales are notoriously complex enough.

If it is hard to understand the impact of the haze on terrestrial habitats, try adding the ocean into the picture. An archipelagic region profoundly linked to its seas, Southeast Asia is recognized as a center of global marine biodiversity. Last year, Zeehan Jaafar from NUS and Tse-Lynn Loh from the John G. Shedd Aquarium in the U.S. wrote that the haze affects marine environments more critically than many understood.

Their paper, published last year in Global Change Biology, hypothesizes that photosynthesis levels in coral reefs, seagrass meadows and mangroves are affected by the same mechanisms that reduce photosynthesis in land plants. Insidiously, thick haze acutely reduces visibility at sea and has been linked with vessel collisions. The region is one of the world’s busiest shipping lanes, where gigantic tankers constantly ply the waters. One hardly wants to think about the ecological disaster a tanker collision would entail.

Indonesia's haze is shown via NASA satellite imagery.
Indonesia’s haze is shown via NASA satellite imagery.

Furthermore, the fires behind the haze create ash and significantly increase topsoil erosion, which the rain eventually washes much of into coastal waters. This sedimentation could further reduce the amount of light available for underwater photosynthesis and also change the chemical composition of the seas, leading to eutrophication, a form of water pollution.

Ultimately, these explanations are hypotheses, and Jaafar and Loh write that there is “an urgent need to fill these gaps in knowledge.” Indeed, it is critical to know if and to what extent this is happening now.

There is an added urgency, for the haze’s impacts could interact with the coral bleaching that might arise from this year’s prolonged El Niño weather phenomenon. Although Southeast Asia is spared for the moment, many reefs elsewhere in the Pacific have already turned an ominous white.

However, when contacted by Mongabay to clarify if any of the unknowns in the paper have been answered one year on, Jaafar’s response was as brief as it was final: “Not that I know of.”

This might be understandable, given the short period between the paper’s publication and the this year’s haze event. But through speaking with other scientists, it became clear that many knowledge gaps had remained unfilled for years.

Botanist Lahiru Wijedasa from NUS said, “We have had haze in 1983, 1997-98, 2006, 2013 and now today, but there have been no studies on its effects on biodiversity and ecosystems. The current fires are pumping more emissions than the U.S., yet we have absolutely no clue about its wider effects.”

Huang was similarly concerned. “If a large mammal like me is getting asthmatic,” she said, “then what about all the other wildlife and plants which are definitely more delicate?” In a separate interview Jain developed the sentiment, and his main worry was that Southeast Asian wildlife lacked the immunity to resist the haze. While most animals’ populations fluctuated naturally in response to weather patterns, he said “haze may mess up with environmental cues that animals rely upon and send wrong triggers. This would have unknown ecological implications.”

A pair of orphaned orangutans in Sabah, Malaysia. Photo by Rhett A. Butler
A pair of orphaned orangutans in Sabah, Malaysia. Photo by Rhett A. Butler

The charity International Animal Rescue (IAR) has worked with orangutans in the West Kalimantan rainforests for years. Ever since the fires started their staff have risked their lives to save the primates from the flames. Yet despite close contact with the orangutans, they do not know how the animals are being affected by the haze.

Karmele Sánchez, IAR Indonesia’s program director, drew parallels between the primates and humans. She said that although only people with weaker immune systems develop respiratory illnesses, all exposed are surely affected. Likewise, in orangutans it should be “pretty much exactly the same.”

She continued, “We do however, know of the existence of an orangutan disease called airsacculitis which is an infection of the air sac. It seems that this disease might be more prevalent during the smoky season. but as far as we know this is not been proven scientifically.”

Finding the silver lining in the smoke, Huang noted that it is now a great opportunity to study the haze’s impact on wildlife. Wijedasa was less sanguine. “I am quite worried at the lack of proper science behind the haze,” he said, “This is not a time to do science after Rome has burned. We need it now.”


Harrison, M.E., Cheyne, S.M., Sulistiyanto, Y., O. Rieley, J. (2007) Biological Effects Of Smoke From Dry-Season Fires In Non-Burnt Areas Of The Sabangau Peat Swamp Forest, Central Kalimantan.

Huang, N. (2015) Maybe monkeys too need N95 masks. The Straits Times, 3 Oct 2015.

Limin, Suwido H., O. Rieley, J., Jaya, S. and Gumiri, S. (2006) The impact of forest fires and resultant haze on terrestrial ecosystems and human health in central Kalimantan, Indonesia. Tropics; Vol. 15, pp. 321-326

Zeehan J., Loh, T-L. (2014) Linking land, air and sea: potential impacts of biomass burning and the resultant haze on marine ecosystems of Southeast Asia. Global Change Biology, 2014; DOI: 10.1111/gcb.12539

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