Where are wild pigs making palm oil farms more destructive than they already are? In Malaysia, whenever look deep enough in the rainforest, there once was an old mystery that needed solving. Even since the late 1980s, scientists who had been working deep inside the Pasoh Research Forest, which is a 1,500 acre piece of forest that is linked to a huge protected reserve, had taken note that this understory was gradually disappearing. And over time, these researchers discovered that all of a sudden could move with ease throughout this jungle. And they could do so without any bushwhacking through the normal tangle of sapling and seedlings. Needless to say, this was a worrisome trend, as the young trees ensure the future life of the forest canopy.
What was Killing the Jungle?
Wild boars were the obvious culprit. These wild pigs tend to snap off saplings and use them use for their nests. Not only that, they trample upon new seedlings, and they continually dig up the soil. But why, all of a sudden, was the rain forest overflowing with these pigs? Immediately, it was suspected that their natural predators – such as tigers – were perhaps in decline.
A scientist named Matthew Luskin was skeptical about this theory. He had devoted many months studying the forests in nearby Sumatra. Specifically, he studied tigers to earn his PhD. He was well aware that if a shortage of predators was causing the problem, then there should an abundance of other prey animals as well – like tapir and deer – but there wasn’t.
In a recent study that post in Nature Communication, Luskin and his associates offer another reason and that is palm oil.
An ingredient that is quite ubiquitous in a whole panoply of grocery store products, ranging from cosmetics to cookies, palm oil has become a very lucrative business—but has also been a disaster environmentally. The specific reason is attributed to the land clearing that is required for the creation of palm oil plantations. This has caused an incredible loss of forest across Malaysia and Indonesia.
Luskin’s research team discovered that these plantations are damaging the forest all around them. And the plethora of palms is why the out-of-control wild boars have been destroying the understory along the Pasoh Forest – not a shortage of tigers.
A Natural Experiment
Typically in forests of southeastern Asia, trees create fruit once every couple of years; and the animal populations will rise and fall with that fruit supply. During most years, there is not much fruit to eat, and this keeps animal populations relatively low.
The Pasoh Forest happens to be surrounded on three of its sides by palm oil plantations. And oil palm trees are by far the most productive fruit trees on the planet—this is why they are so vital commercially—and they will produce fruit nonstop for about 25 years. Luskin believed that the wild boars of Pasoh have been coming to the plantations in order to consume the fallen fruit there. Afterwards, they return to the forest to wreak it ecologically.
When researchers examined that oil palm crop cycle—along with huge amounts of data on tree growth, surrounding boar nests, and oil palm production that had been collected by scientists who worked at Pasoh—this offered an ideal natural experiment to test their hypothesis. So after 25 years when the oil palm trees started to decline, all the growers had to rip up their plantations and begin again fresh. Therefore during the early 2000s, all these growers from around Pasoh cleared out all their old trees and replaced them with new ones.
Suddenly, there was no oil palm fruit at all—and even though environmental conditions had not changed at all in the Pasoh forest itself, the wild boar population crashed dramatically. Within a 125-acre region of the forest, the quantity of boar nests rapidly declined. There were over 300 nests observed before the palms had been cleared to one nest just a couple of years later. And then when the new palms began fruiting, the wild boars returned at the same speed, and there were hundreds of boar nests in just a few years.
Wild boar are extremely destructive when they exist in big numbers. Part of the reason is because they tear up thousands of young trees and then dig up the soil, but another reason is that they like to eat virtually anything they find on the floor of the forest—seeds, eggs, lizards, you name it. And if this wasn’t bad enough, they are capable of reproducing faster than any other large animal on Earth. Each female can have two litters of 9 to 12 piglets annually. And research has indicated that during their peak population periods, wild boars can damage more than half of all saplings in an area.
But Luskin, who is also a research fellow from Nanyang Technological University located in Singapore and the Smithsonian Tropical Research Institute, thinks that macaques could be just as problematic. Their quantities are also rapidly increasing near these palm plantations, and just like the wild pigs they will also eat pretty much anything, from frogs to fruit to chicks. “No one has studied those effects yet,” Luskin points out.
Need Bigger Patches
Actually, ecologists have crafted a name for this sort of phenomenon, as he and his associates have written: When animals that are benefitting from agriculture “extend the ecological impacts of cultivation into food webs far away, in seemingly unaltered areas,” it’s called a “subsidy cascade.”
What was a surprise to the scientists, was the amount to which this subsidy cascaded. After all, these study sites at Pasoh were located fairly deep within the forest, they were at least .8 mile from the edge of the forest and the palms.
Oil palm plantations will often times designate patches of forest that are set aside so that they can be certified as “sustainable” from the Roundtable on Sustainable Palm Oil. These regions of “high-conservation value” forest usually are just very small patches located in a vast area of palm. Luskin, who visited several of these forest patches while in Sumatra, call them “pig and macaque zoos.” He believes these patches are inadequate.
“A solution has been to keep these patches of forest as oases for nature,” he notes. “But that strategy might not work over the long term because of these invisible processes that are happening and are slowly eroding the forest.”
In order to keep rain forest ecosystems from being destroyed palm-fed monkeys and pigs, he continues, we are going to need swaths of forest that are “much larger than we thought before. This paper indicates that we really need to up the size of our forest reserves if we want to have them long-term.”