Lizkimbrough – When a young boy went missing near his mother's rice field in Indonesian Borneo, the entire village searched for him. After nearly a day, he was found near a large strangler fig tree. The boy insisted he hadn't been hiding. Spirits living in the fig tree had called his name and lured him away, he said, then prevented his mother from seeing him even as she walked around the tree looking for him. The family took him to a shaman, who confirmed the boy had been targeted by spirits dwelling in the strangler fig. To protect him from future encounters, they changed his name entirely.
This story, shared with researcher Ditro Wibisono Wardi Parikesit during interviews with an Iban Indigenous community in Sungai Utik, West Kalimantan, illustrates a powerful belief among the community. Almost all (30 out of 32) community members considered large strangler figs to host supernatural entities that may be dangerous if disturbed.
New research published in the journal Biotropica reveals that this belief system has measurable ecological benefits.
Strangler figs grow by depositing their seeds in the canopy of another tree. Their aerial roots grow downward, surrounding and squeezing the host tree until eventually dies. Once the host dies and decays, a hollow root structure supports the fig tree above.
When farmers in the Iban community clear land for farming and encounter a large strangler fig, they protect not only the tree itself but also a buffer zone of vegetation around it. The community calls this practice dipulau, with pulau meaning "island," a reference to the patches of dense vegetation, or tree islands, that remain standing within the cleared agricultural landscape.
This protective area extends approximately 10 meters (30 feet) beyond the edge of the fig's canopy in all directions. Since the fig canopies can range from fewer than 5 m (15 ft) to more than 40 m (120 ft) in diameter, the total protected islands of vegetation vary considerably in size.
Together, these protected zones account for between 1% and 2% of the community's total farmland. While small, these forest islands serve as crucial refuges and stepping stones for wildlife moving through the agricultural landscape.
There are many different species of strangler figs which fruit at different times throughout the year. This cascade of fruiting fogs provides food for wildlife even when other fruit sources are scarce.
The Iban have long understood this. For generations, hunters would wait beneath fruiting figs to catch the primates, hornbills, bearded pigs and other animals that came to feed.
Strangler figs are "ecological keystones," Mike Shanahan, a fig expert who was not involved in the research, wrote in a post about the study in Planet Ficus.
"These trees are disproportionately important in sustaining birds and mammals that disperse the seeds of hundreds of rainforest species," he told Mongabay.
The research team measured and identified strangler fig species across more than 16 kilometers (10 miles) of old-growth forest and 16 km of farmland. They found 25 species in total, with similar densities in farmland compared with forest (1.2 versus 0.9 individuals per hectare).
The fact that strangler figs are just as abundant in the farmland as in the forest is significant, Douglas Sheil, a professor at Wageningen University, Netherlands, and senior author of the study, told Mongabay.
The figs in the farmland also grew to impressive sizes, with canopy diameters averaging more than 16 m (52.5 ft), significantly larger than those in the forest, where other trees compete for the light.
Spirits in the trees
Parikesit recounted another story from his interviews: A grandmother accidentally burned a large fig tree while clearing farmland. She fell ill with symptoms doctors couldn't diagnose. The family brought her to a shaman, who said it was too late, that the spirits had already taken most of her soul. She died shortly after.
The Iban recognize various types of supernatural entities associated with large strangler figs. The most feared is the antu grasi, or hunter ghost, which is depicted in traditional woven mats. One artisan who spoke with Parikesit, said she was obligated to finish the woven mat "by the ghost itself, as she was constantly disturbed during her sleep."
"The bigger the tree, the more spirits that it has inside," Parikesit, who conducted the research during his graduate studies at Wageningen University, told Mongabay. People believe these spirits are connected to their own well-being, and harming the tree can bring illness or death.
Such consequences are known as menawa, a concept that represents the supernatural threat or curse resulting from disrespecting the figs and their resident spirits.
Most Sungai Utik community members identify as Roman Catholics, but many maintain traditional beliefs alongside their Christian faith. However, the study documented early signs of cultural erosion. Two respondents, one a devout Catholic elder dismissive of what he called superstitions, the other who married into the community, reported cutting down large strangler figs without suffering any misfortune.
Douglas Shiel, a co-author of the paper and Parikesit's advisor at Wageningen University the said that some may view research on supernatural beliefs as challenging to the scientific system, "but these are the success stories we need to hear and consider."
"Taboos against harming strangler figs are common to diverse cultures across Africa, South and Southeast Asia, the Pacific and parts of South America, but few studies have considered the ecological impacts of such beliefs, many of which are dying out," Shanahan said.
A replicable model?
The study was carried out in the Sungai Utik Indigenous forest where the Sungai Utik community manages nearly 9,500 hectares (23,475 acres) of land.
According to the study, the community maintains strict protection over old-growth forests while practicing swidden agriculture in riverside plains: Small areas are cleared for crops with fallow areas left to regenerate.
The protected fig tree "islands" represent just one detail within a broader landscape management system, Sheil said, but it's a detail with an "outsized ecological importance."
"The Sungai Utik community's practice of retaining strangler figs and surrounding 'islands' of vegetation when clearing forest to grow crops could be replicated in many other places to make agriculture more biodiversity-friendly and encourage rainforest regeneration when fields are abandoned," Shanahan said.
In fact, planting "tree islands" whether as stepping stones for wilderness corridors or as part of a forest restoration technique (sometimes called applied nucleation) has been studied and seen success, as has the practice of rotating crops.
The Iban's protection of strangler figs illustrates what researchers call "autonomous conservation", or locally developed practices that achieve conservation outcomes without outside intervention. A 2024 literature review of such practices across the tropics found that spiritual beliefs and taboos commonly influence conservation. This occurs through social norms and community respect rather than formal regulations.
"It may be useful to consider framing [the strangler fig study in the Sungai Utik] in the context of local practices that promote and support conservation more generally," said Sheil. "This to me is a vast untapped opportunity."
For Parikesit, what stands out about his research is "the clear bridge between belief and ecology." This study helps to put numbers to the benefits of protecting figs.
However, Parikesi said, it is important to remember that this knowledge belongs to the community. "This knowledge is never ours," he said. "I only borrowed this knowledge to get my degree and also to unravel the secrets behind this ecological process. The first author is the Indigenous people. They are the ones who own this knowledge, not me."
Whether one believes in the antu grasi or recognizes the ecological importance of keystone species, or both, Parikesi said, the outcome remains the same: Protecting strangler figs protects the forest itself.
Banner image: The villagers of Sungai Utik Community prepare for ngerunsur aik ritual, which is believed to clean the river water from any bad presence and bless the river flow to replenish the farmland, in hope to gain abundant yield in the harvest season. Photo by Ditro Wibisono Wardi Parikesit.
Citations
Parikesit, D.W.W., Hardiyanti, Kurniawan, F.H. & Sheil, D. (2025). Strangler Figs and Their Spirits: How Indigenous Beliefs and Practices Influence an Iban Landscape, West Kalimantan, Indonesia. Biotropica, 57, e70089. https://doi.org/10.1111/btp.70089
Bong, I. W., Boissiere, M., Hizbaron, D. R., Setiawan, M. A., & Sheil, D. (2024). Autonomous conservation: A literature review of concepts, local practices, and their relevance in the tropics. Global Ecology and Conservation, 54, e03141.