Palm oil, a leading driver of tropical deforestation, may be also wreaking enormous damage on forests well outside established plantation areas, a new study has found.
The study, published Dec. 20 in Nature Communications, focuses on two decades’ worth of ecological data from Malaysia’s Pasoh Research Forest, a 6-square-kilometer (2.3-square-mile) patch of protected primary rainforest surrounded by oil palm plantations. It found that the forest had been heavily degraded, with the number of understory vegetation — small trees and shrubs that grow between the forest canopy and forest floor — declining by more than 50 percent over the period studied.
“We knew that forest understory was dying, but we didn’t understand why,” said Matthew Luskin, a researcher with the Asian School of the Environment at Singapore’s Nanyang Technological University and the lead author of the study. “Once we started looking outside the forest to the surrounding oil palm, the story became clear.”
The culprits, it turned out, were wild boars, drawn in such great numbers to the oil palm fruit in the adjacent plantations that their nest density within a 50-hectare (124-acre) plot of the research forest swelled a hundredfold.
This “hyper-abundance” of wild boar nests, made using understory vegetation such as tree saplings, coincided with periods when the oil palms were mature and therefore bearing fruit. The nest density dropped just as dramatically during periods of replanting, when no palm fruit was present.
Forest animals such as wild boars and monkeys often raid plantations for palm fruit, whose oil is used in everything from toothpaste and shampoo, to processed foods and biodiesel. In the case of wild boars, this encroachment has an impact well beyond the plantation and deep into adjacent forests, where the animals tear up saplings to build nests for their young.
“Oil palm is also consumed by a number of other native species, including rats, civets and macaque monkeys,” Luskin told Mongabay in an email. “However, the most obvious knock-on effects come from wild boar due to their destructive behaviors in the forest. These include eating tree seeds, rooting up soil, and pregnant mothers building nests which clears the forest understory.”
Compared with areas of the forest that were fenced off to keep out wild boars, the areas where they could roam freely saw the number of their small trees and saplings cut by more than half.
While other studies have investigated the cascading impact on natural food web ecosystems from palm fruit and other human-grown crops, known as food subsidies, the impact highlighted in the new study is more extreme than previously reported, Luskin said.
“This is probably because oil palm produces more fruit than other crops and wild boars are particularly well-equipped to turn food subsidies into new offspring,” he said.
The study found “strong indirect edge effects over decades” in forests more than a kilometer (0.6 miles) from oil palm plantations, “suggesting the true global ecological footprint of human food production has been substantially underestimated.”
The implications of this on the future health of forests anywhere in the vicinity of oil palm plantations are severe, said Matthew D. Potts, a study coauthor and associate professor of forest economics at the University of California, Berkeley.
“What is most concerning about these findings is that the negative impacts of palm oil plantations are occurring deep within what otherwise looks like pristine forest — miles from the nearest plantation,” he said.
Much of the plantations in Indonesia and Malaysia, which supply 80 percent of the world’s palm oil, are carved out of lowland forests and continue to encroach into them. That makes it likely that the same scenario revealed in the study is playing out on a much larger scale.
“I’ve personally observed these same effects occurring across Sumatra as part of another study,” Luskin said. “I’ve also observed these same negative impacts being caused by bearded pigs on Borneo.”
The researchers called on oil palm growers and the governments of the countries in which they operate to take steps to address the issue, emphasizing that “understanding how to mitigate subsidy cascades will be integral to reconcile food production and nature conservation.”
“To limit negative impacts, forest reserves may need to be larger and surrounded by ‘buffer’ areas to limit wildlife access to oil palm fruits,” Luskin said. “A less desirable alternative is the culling [of] wild boars, but this is labor intensive and undesirable for the majority of the local population [whose] religion discourages interaction with pigs.”