Extensive deforestation in Sumatra has corralled the island’s native tigers into fragmented habitats, only two of which contain a sufficiently robust population of the nearly extinct big cat, a recent study suggests.

• Twelve years of deforestation in Sumatra have broken the habitats of its native big cat into smaller fragments, a new study says.
• Only two of the remaining tiger forest landscapes in Sumatra are believed to have populations that are viable for the long term, both of which are under threat from planned road projects.
• The researchers are calling for a complete halt to the destruction of tiger-occupied forests in Sumatra and the poaching of the nearly extinct predator.

The Sumatran tiger (Panthera tigris sumatrae) has since the 1980s been driven to the brink of extinction by a combination of severe loss of habitat — to logging and oil palm plantations — and poaching for its body parts.

The animal’s dwindling population of less than 600 individuals in the wild rates it “Critically Endangered” status, or a step away from extinction, under the IUCN. None of the few scattered tiger subpopulations that remain holds more than 50 individuals.

“I think our report provides the most comprehensive and robust evidence to date that habitat loss [is] pushing Sumatran tigers dangerously toward extinction in the wild,” Matthew Luskin, a researcher with the Asian School of the Environment at Singapore’s Nanyang Technological University, the lead author of the report published Dec. 5 in the journal Nature Communications, said in an email.

Mount Leuser, Kerinci Seblat and Bukit Barisan Selatan National Parks extend from north to south along the western coast of Sumatra. Red and yellow shading shows areas that lost tree cover between 2000 and 2014, according to data from the Global Land Analysis & Discovery lab.

Luskin’s team studied 15 Sumatran tiger forest landscapes, including the national parks listed as UNESCO World Heritage Sites, namely Mount Leuser, Kerinci Seblat and Bukit Barisan Selatan, which run from north to south along the mountainous western coast of Sumatra.

The total population of Indonesia’s last tiger subspecies dropped by 16.7 percent to an estimated 618 individuals in 2012, from 742 in 2000, due to forest loss and habitat degradation, the study said. It also found that the tiger-occupied forests at large declined by 16.5 percent in the same 12-year period.

The total extent of lowland and hill forest, which have higher concentration of tigers, declined by 21 percent, due largely to the expansion of oil palm plantations, according to the study. It also noted that 80 percent of the remaining hill and lowland forest was degraded in quality as of 2012.

“Conservationists want to evaluate the importance of different threats to tigers,” Luskin said. “We found that the primary threat to tiger populations has switched from poaching to habitat loss over the last two decades.”

The habitats have also become significantly more fragmented, leaving the smaller populations at an increased risk of inbreeding, thereby posing yet another threat to their long-term survival, the study said. Only Mount Leuser and Kerinci Seblat national parks have sufficiently large Sumatran tiger populations, with more than 30 breeding-age females each, that can be sustained over the long term.

“Conservationists must know population sizes of endangered species in order to estimate their chance of survival, since small populations often go extinct,” Luskin said. “The Mount Leuser and Kerinci Seblat populations are crucial to the long-term persistence of Sumatran tigers in the wild.”

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• A Sumatran tiger in Gunung Leuser National Park. Photo courtesy Matthew Luskin

The Sumatran tiger is a key conservation focus for the Indonesian government and wildlife activists; two other tiger subspecies native to Indonesia, the Javan tiger (Panthera tigris sondaica) and the Bali tiger (Panthera tigris balica), were officially declared extinct in 2003 due to poaching and habitat loss — the same threats stalking the Sumatran tiger today.

Luskin said clamping down on deforestation and poaching in Sumatran tiger habitats would stave off the march to extinction, to the extent that the habitats could hold over 40 breeding females each and likely sustain the population without supplemental breeding programs for more than 200 years.

“The threats to tigers’ survival in Sumatra are critical,” Luskin said. “We would like a complete stop to all future deforestation and zero tiger poaching in all remaining tiger landscapes.”

But Sumatra’s forests continue to come under threat, most recently in the form of multiple road development plans backed by the government. The planned projects are expected to cut through Mount Leuser, Kerinci Seblat and Bukit Barisan Selatan national parks.

The illegal wildlife trade, meanwhile, continues to flourish. Law enforcement against poaching in Indonesia has been widely criticized as ineffective; perpetrators are rarely prosecuted, and when they are, they receive token sentences that are far lower than the maximum prescribed punishment. Conservationists have also pointed out the seeming impunity in the case of influential figures and officials involved in the illegal wildlife trade.

“We hope [our report] serves as a wake-up call,” Luskin said.

Illegal deforestation for oil palm cultivation in Sumatra in 2015. Photo by Rhett A. Butler

Banner image: A Sumatran tiger at Dublin Zoo in Ireland. Photo courtesy of Neil Turner/Flickr.