- 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.
- Among the threats to Sulawesi’s primate habitat is the growing deforestation for oil palm. The top importers of palm oil as of 2019 were India and China.
The island of Sulawesi in Indonesia that’s home to a unique array of primates found nowhere else on Earth is at the risk of disappearing due to rapid deforestation, a new study warns.
Sulawesi, for a long time, managed to avoid the industrial-scale deforestation that was seen on 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.
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.
“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 wrote 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 about half the size of Kerala.
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 hybridisation 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 hybridisation zones that the researchers looked at are experiencing a “very high” rate of deforestation, Jatna says.
What makes this deforestation more distressing is that none of the hybridisation zones is protected, the researchers say, which makes it almost certain that forest loss will continue in these areas.
Lack of protection
One factor that explains why these hybridisation 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 recognised” 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 need to be initiatives from the government on how to protect [these zones].”
The researchers note that substantial portions of the hybridisation 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.
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.
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.
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 lines and other associated projects in the region, including toll roads, tourism sites, special economic zones, and an upgrade of existing airports.
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
This article was first published on Mongabay.com.
Banner image: Crested black macaque. Photo by Rhett A. Butler/Mongabay.