Nephila sp. Golden orb weaver and oil palm

New study assesses the impacts of oil palm replanting on arthropod biodiversity

Michael Pashkevich writes:

Palm oil seems to be everywhere:  it’s probably in your shampoo, the instant noodles you ate for lunch and – if you’re wearing it – your lipstick.

Michael Pashkevich

In fact, palm oil is the most traded vegetable oil worldwide, in part because it can be used in so many products.

But the production of palm oil is highly controversial. This is because oil palm – the crop that makes palm oil – is often grown in areas that were once tropical rainforests.

Tropical rainforests have the highest levels of biodiversity worldwide, and therefore turning them to oil palm plantations has resulted in large declines in biodiversity and changes to ecosystem processes, too. For instance, turning rainforest into oil palm plantation lowers the number of ants, birds, and primates, such as orang-utans.

Large areas of rainforest have been turned into oil palm plantations. This is bad for biodiversity, but palm oil itself is not bad.

It is incredibly important to protect rainforests, and we must make sure that production of palm oil does not cause deforestation. But we also need to find out how existing oil palm plantations can be managed in ways that benefit the animals and plants that live within them. This is partly because researchers have shown that mature oil palm plantations (roughly 6 years of age or older) are home to large numbers of generalist species. Generalist species are those that can live in a wide variety of conditions. In oil palm, many generalist species provide important services such as pollination, dung removal, and pest control.

Unfortunately, these generalist species may be threatened by the replanting of oil palm plantations. Oil palms are replanted every 20 – 30 years. Replanting is an incredibly destructive process that involves using large machinery to bulldoze mature palms and other aboveground plants. Many plantations in Indonesia and Malaysia (where the majority of palm oil is produced) have already been, or will soon be, replanted. Despite this, we know very little about how replanting will affect biodiversity within oil palm plantations.

Large diggers, such as this one, are used to replant oil palm plantations.

To better understand how replanting of oil palm will affect biodiversity, we studied a chronosequence of oil palm in Sumatra, Indonesia. A chronosequence is a series of planted lands that are all at different ages. For instance, the chronosequence we studied had areas of 30-year-old oil palms that had never been replanted, and areas of replanted oil palms that were 1, 3, and 8 years old.

Chronosequence showing 30 year old, 1, 3 and 8 year old palms (c) Helen Waters

We collected arthropods, such as insects and spiders, in each area of our chronosequence. Insects and spiders are my favourite types of animals, as they can be found nearly everywhere and also are incredibly diverse. For instance, did you know that there is a species of spider in the UK that lives the majority of its life underwater?! After collecting more than 15,000 arthropods, we looked at how their abundance (i.e., the total number of arthropods) and community composition (i.e., the relative number of arthropods within specific groups) changed. We also specifically looked at changes in spider communities, because spiders eat pests in oil palm plantations.

Spiders, such as these mating Nephila sp., eat pests in oil palm plantations.

Our research had a surprising finding:  despite the devastation caused by replanting, we found no differences in the total abundance of arthropods across the chronosequence. This indicated that replanting may have no short- or long-term effects on arthropods. But we also found that replanting changed the composition of arthropods, as the abundance of arthropods in specific groups changed after replanting.

Species of beetle, grasshopper, spider and assassin bug found in a plantation (c) S Steele

For instance, in the first 3 years after replanting, we found that the abundance of beetles (Coleoptera) on the ground and earwigs (Demaptera) and butterflies and moths (Lepidoptera) in the oil palm canopy decreased. We also found that the number of individual spiders and spider species declined in some microhabitats, such as within vegetation that grows up to waist-height.

Nephila sp. (c) S Steele

We think it’s encouraging that replanting did not affect the total abundance of arthropods within plantations. However, we think it’s concerning that specific arthropod groups, such as spiders, were negatively affected by replanting. This is because these groups provide important services, for instance, spiders eat insect pests. 

Ultimately, our research provides vital information on how replanting of oil palm plantations could affect the animals that live there, and the services they provide. If you’re interested in learning more about our research, check out the full article here or our Insect Ecology Group website.

Discover more of the research projects that are based on oil palm plantations in our #BiodiversityWeek: Our Solutions are in Nature resource

Learn more about British spider species from Michael here: Your Friendly Neighbourhood British Spiders

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