- A new study finds promising conservation value in forest corridors along rivers in Sumatra's plantation-dominated landscape.
- But government regulations require areas of forest that border rivers -- called "riparian" forests – be left standing to safeguard water quality for downstream communities.
- In the first study of its kind conducted in the tropics, researchers set camera traps in riparian forests through tree plantations near Tesso Nilo National Park. They found a significant mammal presence, including tapirs, tigers, bears, pangolins, and elephants.
- The researchers say their findings indicate Sumatra's forest remnants could help keep wildlife populations afloat in areas with lots of habitat loss. However, they caution that these corridors are threatened by lax regulation enforcement, and can only work in tandem with larger forested areas.
Amidst Sumatra’s vast tracts of pulpwood plantations, thin slivers of remaining native forest can serve as corridors for large mammals, researchers say. The new study, published last month in Tropical Conservation Science, suggests that maintaining a network of riparian forests – habitat that hugs the banks of rivers and streams – can render pulp and paper plantations more wildlife-friendly.
“More and better riparian corridors can definitely improve wildlife use in plantation areas,” William Laurance, a study co-author and Distinguished Research Professor at James Cook University, said in an email to Mongabay. “I was surprised at how common some species, such as tigers and elephants, appeared to be in these corridors, at least based on signs like their footprints and dung.”
Other rare species, including the endangered Malayan tapir (Tapirus indicus) and critically endangered Sunda pangolin (Manis javanica), were also shown to use thin strips of forest embedded in an otherwise inhospitable landscape.
“[This research] shows that, with some provisions, we can maintain connectivity across productive landscapes, which is important for many ecological processes,” Robert Nasi, a Research Program Director at the Center for International Forestry Research (CIFOR), said in an email to Mongabay. Nasi was not affiliated with the study.
Pulpwood plantations are spreading across Indonesia at a remarkable pace, the study states. If national targets are met, land under pulpwood production – now nearly five million hectares – will triple by 2030 and cover an area larger than the state of New York.
According to the study, pulpwood plantations – which are predominantly comprised of acacia and eucalyptus trees – often supplant large swaths of native forest. In Sumatra alone, one of Indonesia’s largest islands, pulp and paper plantations replaced an estimated 1.2 million hectares of forest between 2000 and 2010.
But even in plantation landscapes, some native habitat remains, the researchers say.
That’s largely due to Indonesia’s national policy. By law, pulpwood plantation owners are required to retain native habitat along rivers – called “riparian forests” – when the landscape is converted, the study states. The law was intended to protect downstream communities by shielding waterways from sedimentation and plantation runoff, such as pesticides, the researchers say. But riparian forests may provide other benefits, as well.
In landscapes dominated by industrial plantations – which cover about 13 percent of Indonesia’s land area – research suggests that riparian forests can function as corridors that connect disparate chunks of native habitat. Corridors are especially important for animals that range widely and depend on forest cover to travel, like clouded leopards (Neofelis nebulosa) and other vulnerable species, research shows.
But prior to this study, research on riparian corridors had been restricted to temperate regions. Scientists didn’t know if animals in tropical Asia – especially large mammals – could use riparian forests to traverse through production landscapes, the researchers say.
“There was quite a bit of literature in temperate climates, but in the tropics there just wasn’t much at all,” lead author Betsy Yaap, a doctoral student at James Cook University, told Mongabay.
In the summer of 2011, she and her team set out to change that.
The researchers traveled to an industrial acacia plantation in Riau, Sumatra, where they set up a series of camera traps within remaining native habitat – slivers of riparian forest. Like home security cameras, camera traps are triggered by movement; when an animal walks by, the camera snaps a photo and “traps” the species in a digital catalog. Distributing traps systematically across a landscape for a set period of time provides ecologists with a relatively simple tool to measure the abundance and diversity of mammals.
The team distributed traps within a few different types of riparian corridors. They laid some in corridors surrounded by a barren landscape – where acacia had been recently harvested – and set up others in corridors bordered by fields of mature acacia. The researchers also placed camera traps at varying distances to a large block of native forest: Tesso Nilo National Park.
Then they waited.
Over a period of several months, the traps caught a total of 19 species of large mammals in the riparian corridors – about half of what you might expect in a native Sumatran forest, the researchers write. But according to Yaap, that’s a lot.
“I was impressed and delighted with how many species we detected in the plantation, especially ones of conservation importance,” Yaap said.
The cameras even detected mammals in corridors surrounded by barren land, the study states. These include four species listed as threatened by the International Union for Conservation of Nature (IUCN) – the pig-tailed macaque (Macaca nemestrina), sun bear (Helarctos malayanus), Malay tapir, and Sunda pangolin – and all but one species that tigers pray upon. According to the study, this suggests that vulnerable and important species may be able to travel through an inhospitable landscape using a network of riparian corridors.
As the researchers expected, the greatest number of species, including the charismatic and critically endangered Sumatran tiger (Panther tigris sumatrae), were detected in the riparian forests closest to Tesso Nilo National Park.
The researchers also searched for patterns in their data that might reveal how variables like corridor width and distance to the national park influence where species are most likely to be spotted. This analysis was especially revealing for the Malay tapir, which was shown to favor wider remnants where greater forest cover is available. The results have implications for corridor design, the researchers say.
“Corridor design in landscapes with this species should focus on creating wider corridors and access to additional forest habitat to accommodate their needs,” the study states.
The “ideal width” of a corridor has been a matter of debate for some time, researchers say. In fact, there are large, ongoing projects to study it.
Undoubtedly, how wide a strip of forest must be to serve as a corridor will vary species to species, the researchers say. But for large mammals in Sumatra, Yaap’s team has an answer of sorts: 100 to 200 meters.
“Our corridors of remnant native riparian forest mostly ranged from 100 to 200 meters in width,” the paper states. “We believe this is a reasonable minimum width…to serve as movement corridors for large mammals in Sumatra.”
At face value, this is good news for wildlife in Indonesia, Laurance says. Regulations in Indonesia require that pulpwood plantations maintain riparian forests that spread 50 to 100 meters on either side of the river, which matches up with the range that the researchers deem “reasonable.”
But it’s not that simple, the researchers say. Regulations for riparian forests – while holding great potential for wildlife conservation – may not offer reliable protection.
According to Laurance, “The law is not being consistently applied or enforced and, as a result, the width and continuity of riparian corridors is highly variable among different plantations…”
Laurance also emphasized that even where riparian corridors are intact and well-connected they, alone, are insufficient to support long-term wildlife conservation. Large tracts of forest, absent of hunters, will always be required.
“Having riparian areas is far better than having no native forest at all,” Laurance said. “Though at the end of the day, most of these species are going to need large, intact landscapes with little or no hunting in order to survive in the long term.”
In other words, corridors need to lead somewhere.
In Sumatra, that “somewhere” may already be at risk. Data from the University of Maryland visualized on the forest monitoring platform Global Forest Watch reveals that Tesso Nilo National Park has lost around 65 percent of its tree cover over the last decade – largely due to illegal oil palm development and forest fires.
The destruction of the park, much of which occurred after this study took place, may impact if and how wildlife use riparian forests, the researchers say. And that’s a topic for future research.
“Good follow-up research would be to go back to the same site, now that years have passed, and see if these remnants are still actively being used by these species,” Yaap wrote in an email to Mongabay. “[We don’t know] if they are even present in the landscape anymore.”
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Editors note: William Laurance is a member of Mongabay’s advisory board. In that role he has no influence over content or editorial decisions.