Amid the tropical rainforest in the Hadabuan Hills Ecosystem, where Siamang and Agile gibbons cry out and where Rhinoceros hornbills and Black hornbills growl and cackle above the forest canopy, survey work by a Korean hydroelectric company has just wrapped up, and construction is slated to begin in 2020 on a dam called Siborpa Hydroelectric Power Plant.

The Hadabuan Hills isn’t a national park or a wildlife sanctuary; about half of it is considered a hutan desa, or village forest. It is essentially a cluster of steep mountains that were too difficult to cultivate quickly and easily, and were thus spared wholesale conversion to oil palm plantations due to the challenging topography.

So far we have confirmed the presence of tigers, clouded leopards, marbled cats, golden cats, Malayan tapirs, sun bears, leaf monkeys, the fast-disappearing Sumatran Laughingthrush, and a plethora of other wildlife. If this place isn’t a national treasure, we don’t know what is. To see it badly scarred by a hydroelectric dam of questionable use and value would be deeply disturbing.

This post is a commentary. The views expressed are those of the author, not necessarily Mongabay.

The general public knows about the precarious situation of the world’s mostly recently identified great ape — the Tapanuli orangutan — within the Batang Toru Ecosystem. There, the construction of a Chinese-backed dam is underway, a questionable development scheme that is already sending orangutans fleeing out of the forest and into nearby farmlands. This is a highly distressing situation, made all the more so because this forest is also home to other species listed by the IUCN as Critically Endangered, such as the Sumatran tiger.

But not many people know about another brand new dam going up in a relatively unknown forest ecosystem not far from Batang Toru — the Hadabuan Hills Ecosystem. There, amid the jungle walls of tropical rainforest, where Siamang and Agile gibbons cry out and where Rhinoceros hornbills and Black hornbills growl and cackle above the forest canopy, survey work by a Korean hydroelectric company has just wrapped up, and construction is slated to begin in 2020 on a dam called Siborpa Hydroelectric Power Plant. The dam is named after a beautiful waterfall by the same name — Siborpa — that it will destroy, as it will be built on the Bila River close to the waterfall. This seems like a particularly cruel twist, naming a killer after its victim.

To the best of our knowledge, not a single Western scientist or tourist has ever glimpsed this waterfall, which roars off a narrow and jagged escarpment into the deep and swift Bila River, which flows southeast to the city of Rantau Prabat in North Sumatra province, where it then glides through palm oil plantations before emptying into the Strait of Malacca.

The Hadabuan Hills isn’t a national park or a wildlife sanctuary; about half of it is considered a hutan desa, or village forest. It is essentially a cluster of steep mountains that were too difficult to cultivate quickly and easily, and were thus spared wholesale conversion to oil palm plantations due to the challenging topography. The PRCF Foundation, Habitat ID (headed by Gregory McCann), and the local grassroots organization Sumatran Tiger Rangers (headed by Haray Sampurna Munthe), have been carrying out camera trap reconnaissance surveys in the area, as well as occasional forest patrols, for the past three years. So far we have confirmed the presence of tigers, clouded leopards, marbled cats, golden cats, Malayan tapirs, sun bears, leaf monkeys, the fast-disappearing Sumatran Laughingthrush, and a plethora of other wildlife. If this place isn’t a national treasure, we don’t know what is.

It may be a forgotten, leftover land of rare species, but that doesn’t mean that the Hadabuan Hills has fallen off the radar of local and international developers. Construction of the 114-megawatt Siborpa Dam will not only plug up this section of the Bila River and doom the gorgeous Siborpa waterfall, but a series of access roads will likely need to be punched through healthy forests, scattering tigers, tapirs, and hornbills just as the Batang Toru dam is sending the Tapanuli orangutans packing. In fact, a villager told us that a tiger recently strolled right into the tent camp of the Korean survey engineers, who ran for their lives. It’s a picturesque tale, but it is unlikely to repeat — or at least, to result in a similarly benign outcome — when the heavy construction equipment rolls in and sturdy workers’ barracks go up.

Thirty or forty years ago, Batang Toru and Hadabuan Hills, which are about 70 kilometers apart, were connected by lowland forest, which is one of the reasons why we thought there might be some credence to villager reports that orangutans had been sighted in Hadabuan Hills in recent years. For our 2017 expedition, we brought in primatologist Julia Mӧrchen, a PhD candidate from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, to assess the possibility of an orangutan presence. She found that the high fruit abundance and diversity found in all elevations (more than 93 fruits and flowers documented, from a range of 300 to 2,000 meters above sea level), as well as the abundant presence of at least five different primates species, distinguish the area and fulfill the criteria of being a good habitat for orangutans.

Although we gathered several independent reports of local villagers sighting orangutans and their nests or hearing the “longcalls” of males in different locations around Hadabuan Hills, the short time period of the expedition didn’t allow us to gather direct evidence of the great ape’s presence. Therefore it becomes clear that we need an orangutan-specific second expedition with a different strategic approach of spending more time in the area with a much smaller number of people, which would allow us to survey the area specifically and in more detail.

Most likely orangutans were present in Hadabuan Hills decades ago — the question is whether or not a relic population persists or even just some individuals remain. According to Julia Mörchen, these individuals will most likely belong to the newly recognized species of the Tapanuli orangutan, Pongo tapanuliensis. However, due to the high elevation, the population density would probably be very low. But, orangutans or not, the Hadabuan Hills is a biological gem that deserves full protection from the dams, palm oil plantations, and poachers that now threaten it.

This is a place where magic-eyed tigers entice monkeys and gibbons to fall from trees through hypnotism, and so well-known is this “magic” to the primate community that gibbons and monkeys have reportedly taken to sleeping on branches that overhang rivers so that if they fall during the night — nudged off a branch from down below by the tiger’s powerful pupils — they’ll have at least a fighting chance at survival in the swift-moving rivers. Anecdotal reports also describe tigers stealing recently gutted fish from evening campsites where fishermen were just an arm’s length away, with the big cats either partially submerged in the river or crouching low in the gloom of the nearby foliage; some tigers, so the stories go, unwilling to creep too close to camp, will swat the ground several times in succession with their mighty paws, demanding a tasty river fish from the human intruders, until those intruders toss a few to harimau, King of the jungle.

And it is not just wildlife, rivers, and jungles that are of interest in this little-known ecosystem. Rock carvings, of possibly ancient, pre-Islamic origin, have been found chiseled into a limestone cliff beside the Bila River. Rock carvings are pretty much impossible to date, so the images have to be compared stylistically to other similar carvings from the region. Rock carvings of insects and hornbills(?) are somewhat unusual, and probably better pondered by professional archaeologists. It is possible that more carvings will be found, while a couple thousand feet above the river, in the village of Lobu Tayas, large stone carvings of what are apparently ancient kings or gods have been found and are looked after by villagers. The Hadabuan Hills is therefore a natural and cultural treasure for Indonesia.

We called it a “leftover land,” but the Hadabuan Hills has got to be one of the prettiest places in Sumatra, and that’s saying something. To see it badly scarred by a hydroelectric dam of questionable use and value would be deeply disturbing. We have seen what dams do in the tropics: it is like some kind of famine has ravaged the biodiversity, leaving behind a dead, broken, and drowned ecosystem. This cannot be allowed to happen to yet another biodiversity hotspot in Indonesia.

Is there any hope? Any plan? We would like to install several camera traps in and around the dam construction site to show the government that nationally protected species such as tigers and tapirs reside in this area, in order to get them to reconsider this project. We have started a crowdfunding campaign to help pay for it.

Big business almost always wins in situations like this; maybe the tigers can work some of their magic for us and stop the Siborpa Dam.

Gregory McCann is the Project Coordinator for the NGO Habitat ID and the author of Called Away by a Mountain Spirit: Journeys to the Green Corridor.

Haray Sampurna Munthe is the founder of Sumatran Tiger Rangers.

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