Keith Anthony Fabro – Off the western coast of Sumatra, the Mentawai Islands rise from the Indian Ocean in a patchwork of emerald forests and winding rivers. The canopy shelters endemic macaques and gibbons, hornbills and orchids, while coastal villages still echo with rituals that tie people to the land and sea.
Among the younger generation of Indigenous Mentawai, an ancestral belief system known as Arat Sabulungan continues to influence how forests are understood and used. The cosmology teaches that every tree, river and animal is alive with spirits whose balance must be honored. Although the influence of world religions is eroding these beliefs, researchers have found that Indigenous youths are balancing the two. Young islanders who grow up attending church services or mosque prayers still join their elders in ritual clearings, offering chants and tokens before cutting trees or casting fishing nets.
"Mentawai youth today reinterpret their ancestral heritage in diverse ways," researcher Dwi Wahyuni from Imam Bonjol State Islamic University in Padang, on the Sumatran mainland, told Mongabay.
This practice remains central to their identity – but it is also under strain. Logging, modernization and shifting values test how faithfully this balance and the traditional beliefs are carried forward.
In a recently published study, Dwi and colleagues from Imam Bonjol set out to understand this tension. Conducted in five villages on the Mentawai islands of Siberut and Sipora, the ethnographic work examined how Mentawai youth are blending Arat Sabulungan with Christianity and Islam, and what this means for both culture and conservation.
But some researchers have been quick to caution against drawing quick conclusions from the findings. The study, they said, leans on brief fieldwork, overlooks cases where rituals coexists with logging operations, and can lead some to romanticize Indigenous spirituality for modern conservation goals.
Not forgotten
According to Mentawai belief, the world is split into two realms: the visible, where forests, rivers, seas and people exist, and the invisible, home to guardian spirits. Every being is said to carry both a simagere (life force) and a ketsat (soul), which return to the spirit world after death. Watching over both realms is Ulaumanua, a "supreme light" believed to sustain all life.
Islam arrived in the Mentawai Islands in the 18th century, followed by Protestant missionaries in 1901 and Catholic ones in 1953, but these didn't erase the Indigenous cosmology. Instead, the islanders took elements of the new religions and mixed them with the old. Many Mentawai today equate Ulaumanua with the biblical God or Allah, and view long-held forest taboos as not only ancestral rules but also acts of divine stewardship.
The study records 11 rituals that link spirituality to environmental management, many of them still central to daily life for Mentawai elders and youths alike. One example: before felling a tree, families perform buluat, an offering to honor the tree's spirit. They also commit to replanting fruit trees like durian or rambutan on the cleared spot. "Any trees we clear are replaced... If we do not replant, the land will not thrive," the study quotes one elder as saying.
A sikerei, or shaman, in Siberut described how restraint guides forest use. Wood is taken only for essentials such as building houses or canoes, and these customs are carefully passed down. These traditions act as safeguards against unsustainable logging, ensuring balance between people and nature, the researchers write.
For younger generations, these traditions are far from forgotten.
In Matotonan village on Siberut, young Muslims, many of them university graduates now serving as village officials, have revived Liat Pulaggajat, the village's anniversary celebration. "[Liat Pulaggajat] is understood both as a tribute to ancestral teachings and as a means of fostering solidarity and community development," Dwi said.
Meanwhile, Catholic youths from Siberut now living in Tuapejat, the Mentawai administrative seat on the island of Sipora, continue to follow ancestral taboos in their daily lives, the researchers documented. "Even while living in the regency's administrative center, they still practice elements of Arat Sabulungan as part of their identity," he added.
Local cultural NGO Yayasan Pendidikan Budaya Mentawai (YPBM) said these findings match what it sees through its own cultural and ecological education program, which teaches young people about Mentawai traditions and their ties to the natural world.
"Young people involved in our cultural programs demonstrate an appreciation for both religious and cultural/traditional identities," YPBM told Mongabay. "There's an ongoing negotiation around adapting, syncretizing, or reinterpreting traditional practices that may conflict with formal religious teachings so they remain relevant and (relatively) accepted in both religious and Indigenous communities."
According to YPBM, many young people, though raised in faiths like Islam or Christianity, still respect traditional institutions such as Arat Sabulungan, the sikerei and nature-related taboos. Practices like eeruk uma (clan house cleansing) or restrictions on cutting certain trees without customary permission remain part of community life.
"Arat Sabulungan functions as a value system, a set of social norms, and conservation principles," YPBM said. "It is not merely a set of rituals, but a guide for how the community understands relationships between humans, spirits, forests and the wider environment."
Pressures on forests, pressures on beliefs
Despite its persistence, Arat Sabulungan faces mounting threats. The forests themselves form part of the Sundaland biodiversity hotspot, sheltering endemic species such as the Siberut macaque (Macaca siberu) and Kloss's gibbon (Hylobates klossii). Beyond their rich biodiversity, these forests regulate climate, store carbon and sustain local livelihoods.
Yet decades of logging have stripped bare large tracts of Siberut, the study noted. Exploitation dates back to the 18th century. A logging moratorium in 1993 was lifted in 2001, opening 100,000 hectares (about 250,000 acres) to new concessions. Around the same time, decentralization of political power from Jakarta to the provinces and districts saw local officials issue a flurry of new permits. By 2006, about 3 million cubic meters (106 million cubic feet) of timber had been removed from the Mentawais, showing how market demand trumped the customary bans.
"Forest exploitation by large companies and local actors has caused massive deforestation, resulting in disrupted ecosystems including the erosion of biodiversity and natural resources that support the lives of Indigenous peoples," the new study said.
While the Indigenous Mentawai uphold strong conservation values through their rituals and customary rules, the researchers noted that external economic and political forces often override them.
"Indigenous communities lack sufficient power and receive inadequate support from authorities to resist exploitation," the study said. "This highlights the need for more responsive policies that respect local wisdom and protect ecosystems in areas vulnerable to commercial exploitation."
For the Mentawai, deforestation represents not just ecological loss but also a spiritual one. The study noted that "the loss of forest areas does not only cause ecological damage but also undermines the socio-cultural systems... including the role of sikerei and traditional rituals that depend on forest resources" – practices shared by both elders and youths that have weakened as landscapes shrink.
Critiques, policy action call
But not all scholars are persuaded by the study's optimistic framing.
Darmanto Darmanto, an anthropologist at the Czech Academy of Sciences' Oriental Institute, told Mongabay the paper barely explains what Arat Sabulungan is at its core and doesn't engage much with classical scholarship on the topic.
He also noted that it doesn't discuss buluat (offerings) and buluakenen (acts of giving), which he calls "the primary methods of understanding others and transcending the human and non-human perspectives."
Darmanto said Arat Sabulungan neither automatically prevents the Mentawai from exploiting the forest nor provides an ethical foundation to support modern conservation, pointing to cases where shamans have conducted offerings before logging operations.
He also critiqued the methodology – one month of fieldwork in five villages – as insufficient for such a complex subject, and questioned the quick turnaround from fieldwork to publication. The study's framing, Darmanto said, is "a classic trope of the good kind of primitive spiritualist that an urban audience wants to hear about."
Dwi acknowledged these critiques but said the study's aim was to explore "the broader cosmological structures of Arat Sabulungan and how they shape people's relationship with nature," rather than serve as a full ethnography. He noted that future work could look more closely at rituals of offering and exchange.
He agreed that rituals can work in different ways – sometimes limiting resource use through taboos, but also allowing extraction before tree felling.
"Rather than depicting them as purely green traditions, I suggest they form a cultural framework for negotiating human-nature relations," he said, adding that he sought to avoid romanticizing Indigenous spirituality as always conservationist.
Dwi also acknowledged that one month was a short period in which to carry out the fieldwork, but said he used focused techniques, including interviews and observations. He also said his analysis considered broader forces such as logging, modernization and state religious policies.
"My argument is precisely that Mentawai cosmology cannot be understood in isolation from these political-economic dynamics, " he said. "I aim to show how religiosity interacts with broader structural challenges in a way that is complex and sometimes contradictory."
Ultimately, the fate of these traditions is tied to the fate of the forest, the authors say. Lacking political power and state backing, communities are exposed, and the authors urge policies that respect local wisdom and secure Indigenous rights.
"Ongoing forest destruction threatens the continuity of this cosmological space," Dwi said. "When sacred trees and ritual plants disappear, young people lose direct opportunities to learn and experience these practices. This makes the role of youth both fragile and vital – fragile because of ecological disruption, but vital because they serve as bridges between ancestral traditions, world religions, and modern community building."
Citations
Wahyuni, D., Octavia, I. A., Karista, K., Sabna, A., & Martalia, M. (2025). The religious cosmology of Indigenous communities for maintaining ecological balance in the Mentawai Islands, Indonesia. Millah: Journal of Religious Studies, 137-172. doi:10.20885/millah.vol24.iss1.art5
Persoon, G. A. (1997). Defining wildness and wilderness: Minangkabau images and actions on Siberut (West Sumatra). In G. Benjamin & C. Chou (Eds.), Tribal Communities in the Malay World: Historical, Cultural, and Social Perspectives (pp. 439-456). doi:10.1355/9789812306104-021