- Unique primate habitats on the Indonesian island of Sulawesi are under threat from rising deforestation, according to a new study.
- The island’s isolation has allowed macaques and tarsiers there to evolve in unique ways, leading to an “explosion” of biodiversity found nowhere else across Southeast Asia.
- But logging, expansion of farmland, and infrastructure projects are driving a growing rate of forest loss, including in the “hybridization zones” that are a key factor in the island’s rich variety of primate life.
- While protected areas exist on Sulawesi, they’re concentrated located at higher elevations, while most of the primates occur in lowland forests that can be more easily cleared and farmed.
JAKARTA — An evolutionary crucible in Indonesia that’s given rise to a unique array of primates found nowhere else on Earth is at risk of disappearing due to rapid deforestation, a new study warns.
The island of Sulawesi lies in the Wallacea biogeographical region, where the native fauna are distinct from the better-known wildlife — such as orangutans, rhinos and tigers — found in the western half of Indonesia. While the latter region was once part of the Southeast Asian landmass when sea levels were lower, thus sharing much of the same biodiversity, Sulawesi has always been isolated from the mainland, which has allowed the wildlife there to evolve in unique and striking ways.
It’s a haven in particular for primates: all 17 species of macaques (Macaca spp.) and tarsiers (Tarsius spp.) found there are endemic to the island. But these evolutionary marvels are under threat from the accelerating loss of their pristine habitat.
Sulawesi for a long time managed to avoid the industrial-scale deforestation that ravaged the islands of Sumatra and Borneo for oil palm plantations and coal mines. But as land and resources are depleted in western Indonesia, developers are turning increasingly to the relatively untouched islands of the country’s east, including Sulawesi and Papua.
“Although not yet as severe or dramatic as deforestation rates in Sumatra, drivers of deforestation in Sulawesi are increasing in intensity,” a group of researchers from Indonesia and Australia write in a recent paper.
Published in the journal Global Ecology and Conservation, the study notes that clearing of Sulawesi’s lowland forests for farmland began in the 1990s, continuing on into the 2000s and 2010s and eating away at crucial habitats of endemic and endangered primates. Using forest loss data from Global Forest Change, backed up by three visits to the island in 2019, the researchers found that deforestation rates had increased in the habitats of all of the primates of Sulawesi.
They calculated that Sulawesi had lost 11% of its forest cover from 2000 to 2017 — an area of more than 2 million hectares (5 million acres), or twice the size of Jamaica.
Among the primates hit hard by the deforestation are the booted macaque (Macaca ochreata) and the Peleng tarsier (Tarsius pelengensis), both of which are threatened species that have lost 14% of their habitat. Other species have lost a smaller percentage of their habitat, but some had a restricted range to begin with, making any loss of forest significant.
The most threatened of Sulawesi’s macaques is the Celebes crested macaque (M. nigra), which shot to pop culture prominence in 2011 when one of the monkeys shot a series of “selfies” that would go on to be the subject of a protracted copyright wrangle. The crested macaque is classified as critically endangered on the IUCN Red List. It has a population of 4,000 to 6,000 individuals throughout the Sulawesi mainland and 100,000 on nearby Bacan Island.
Despite much of the monkey’s range being protected area, its habitat is still shrinking rapidly due to large-scale deforestation for logging and agriculture, some of which is subsidized by the government. The Celebes crested macaques lost 7% of its habitat between 2000 and 2017, the study says.
For study lead author Jatna Supriatna, a conservation biologist from the University of Indonesia, what makes the forest loss in Sulawesi particularly invidious is that it affects areas known as hybridization zones — regions where closely related primate species interbreed and fuel the explosion of biodiversity seen in few places on Earth.
“Hybrid zones are very important for science [because] there’s a lot of genetic differentiation there,” Jatna tells Mongabay.
“For example, there are one to two macaque species in Java and Borneo. But in Sulawesi, the number is seven. That means there’s an explosion,” he says. “The same goes with tarsiers. There’s one in Borneo, one in the Philippines, but there are more than 10 in Sulawesi.”
Yet all six of these crucial hybridization zones that the researchers looked at are experiencing a “very high” rate of deforestation, Jatna says. Within a 10-kilometer (6-mile) radius of the hybridization zones, a combined area of more than 80,000 hectares (200,000 acres) of forest were lost. Within a 50-km (30-mi) radius, the deforested area was nearly 540,000 hectares (1.3 million acres).
The highest forest loss occurred in the hybrid zone between the western populations of the booted macaque and Tonkean macaque (Macaca tonkeana): nearly 26,000 hectares (64,000 acres) within a 10-km radius, and 152,000 hectares (376,000 acres) within 50 km.
What makes this deforestation more distressing is that none of the hybridization zones is protected, the researchers say, which makes it almost certain that forest loss will continue in these areas.
The study identified some ongoing threats to the hybridization zones, including a project to widen a road through the very narrow zone between the ranges of the Tonkean macaque and Heck’s macaque (Macaca hecki) in Central Sulawesi. More than 48,000 hectares (119,000 acres) of forest cover has already been lost within 50 km of this zone, and the road project could lead to greater human occupancy of the zone, accelerating the pace of deforestation.
The researchers also found increased clearing of forest for farmland in South Sulawesi, in the hybrid zone between the Tonkean macaque and the moor macaque (Macaca maura). They warn the expansion of corn, cocoa and coffee plantations is likely to continue here.
Lack of protection
One factor that explains why these hybridization zones are being deforested is that they don’t fall within protected or conservation areas.
“Hybrid zones have existed for hundreds of years but it wasn’t until 1984 that they were recognized” as being important, Jatna says. “I have proposed [protecting these zones], but maybe because there are already many people and settlements in these areas and forests, there’s been no [follow-up] yet. So there needs to be initiatives from the government on how to protect [these zones].”
The researchers note that substantial portions of the hybridization zones identified in the study have been proposed for protection. But Indonesia’s conservation laws don’t recognize the biological importance of such areas, much less the need to protect them, Jatna says.
“We can’t let these hybrid species disappear just like that because they lose their habitats,” he says. “That’s why these zones need to be protected.”
Also falling outside the scope of protected areas are the entire ranges of species like the Lariang tarsier (Tarsius lariang), spectral tarsier ( Tarsius tarsier) and Siau Island tarsier (Tarsius tumpara). The latter is considered critically endangered.
“The remaining habitat of these three species, covering only a few thousand hectares, is not enough for them to survive unless the forest remnants in which they occur become protected and carefully managed,” the researchers write in their paper.
While large protected areas do exist, notably Lore Lindu National Park and Morowali Nature Reserve, they’re concentrated in Central Sulawesi, leaving other regions with little or no protection. They’re also located at higher elevations that are unsuitable for agriculture — and thus less likely to be targeted for deforested — while most of Sulawesi’s primates occur in lowland forests that can be more easily cleared and farmed.
Farming and infrastructure
Establishing more protected areas is crucial to saving Sulawesi’s unique primates, Jatna says. But it’s just as important to address the drivers of deforestation. These include extensive logging and wood harvesting, agricultural expansion, and infrastructure development, according to the study.
While the scale of logging in Sulawesi pales in comparison to Sumatra and Borneo due to the island’s lack of accessible lowland forest and fewer commercially valuable tree species, it’s still a major driver of deforestation. Logging, even selectively, also provides room for people to move in and start clearing land for farming, accelerating the spread of deforestation.
In some cases, the expansion of farmland is encouraged by government policies. The government of Gorontalo province, at the northern edge of Sulawesi, has since 2008 pushed for the establishment of corn farms there, including offering incentives such as minimum price guarantees.
The proliferation of corn farms poses a threat specifically to Jatna’s tarsier (Tarsius supriatnai), a species named after the primate researcher. It was only described in 2017, but has already lost an eighth of its native habitat.
“In Gorontalo, the former governor, Fadel Muhammad, pushed for all [land] to become corn plantations,” Jatna says. “That’s a really bad policy … The result is the degradation of the forests.”
Another crop threatening Sulawesi’s primate habitat is oil palm, already closely associated with the wholesale destruction of forests in Sumatra and Borneo. The study notes that since a new road was recently built close to Nantu Wildlife Reserve in Gorontalo, oil palm farms have grown significantly. They attribute this to the presence of the road improving accessibility to new land.
The study identifies several other infrastructure projects that could lead to increased deforestation, such as the construction of a railway line from Makassar in southwestern Sulawesi to Parepare 150 km (93 mi) north. The line is part of the 1,513-km (940-mi) Trans Sulawesi network, the largest infrastructure development in Sulawesi, that’s expected to link the island’s south to the north.
The Trans Sulawesi project is in turn being developed as part of China’s Belt and Road Initiative (BRI). As such, the Indonesian government plans a slew of other associated projects in the region, including toll roads, tourism sites, special economic zones, and an upgrade of existing airports.
“This may lead to increased road development, which increases access and provides opportunities for encroachment into the forests that remain,” the study says.
Supriatna, J., Shekelle, M., Fuad, H. A., Winarni, N. L., Dwiyahreni, A. A., Farid, M., … Zakaria, Z. (2020). Deforestation on the Indonesian island of Sulawesi and the loss of primate habitat. Global Ecology and Conservation, 24, e01205. doi:10.1016/j.gecco.2020.e01205
Banner image: A Sulawesi black macaque in the Tangkoko Batuangus Nature Reserve. Photo by Rhett A. Butler/Mongabay.
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