Growing rubber drives more deforestation than previously thought, study finds

Rubber cultivation in Southeast Asia is responsible for double or even triple the deforestation previously attributed to it, according to a recently published study.

Antje Ahrends, one of the study’s authors, said she wasn’t surprised by the findings. Over the years, Ahrends, head of genetics and conservation at the Royal Botanic Garden Edinburgh, had observed first-hand how rapidly rubber plantations were spreading in Southeast Asia. This, she said, made her think that previous estimates linking rubber cultivation to around 1 million hectares (2.5 million acres) of forest loss since 2000 had underestimated the scale of the issue, leading to oversights in policy setting and implementation.

Now, thanks to remote-sensing technology paired with on-the-ground verification, she and her team have data to back up their observations from field trips over the years. Using remote-sensing technology, the team mapped 14.2 million hectares (35.1 million acres) of rubber plantations across Southeast Asia. Their study, published in the journal Nature, found that 4 million hectares (about 10 million acres) of forest have been cut down for rubber plantations since 1993, with at least half of that area chopped down since the turn of the millennium.

Of the 14.2 million hectares mapped in the study, more than 1 million hectares were found to be in areas that are vital for the survival and protection of biodiversity.

“This shows that rubber deforestation has been underestimated and has essentially not received the attention it deserves in policies,” Ahrends told Mongabay in a video interview.

While the methodology used in the study has been deployed to map crops before, it hasn’t been done for “such an extensive region,” Jefferson Fox, senior fellow at the East-West Center who has studied land use and land cover change in Southeast Asia, told Mongabay in an email interview. Fox said the actual area of deforested land might even be much higher, because the study doesn’t account for forests that were cut down for other purposes and later converted to rubber plantations. “In Northeast Thailand, for example, large areas currently in rubber, were deforested for cassava for European livestock feed,” said Fox, who wasn’t involved in Ahrends’s study.

Cultivation of crops such as oil palm, soy, cacao and rubber, among others, is the major cause of deforestation around the world. According to a report published by the U.N.’s Food and Agriculture Organization in 2021, agricultural expansion drives 90% of global deforestation, with a vast majority of it occurring in tropical forests.

Demand for rubber, as with these other commodity crops, is driven by the vagaries of the market. Growing consumer demand for vehicles, including electric ones, means growing demand for rubber to make more tires. And while the majority of the rubber produced today is synthetic — a petroleum byproduct — natural rubber still accounts for 30% of global production. A study, led by Eleanor Warren-Thomas of Bangor University and co-authored by Ahrends which was published earlier this year in the journal Conservation Letters, documents how rubber plantation areas expanded by 3.3 million hectares (8.2 million acres) between 2010 and 2020.

However, despite the alarming findings, tracking and monitoring forest loss related to rubber is often difficult. For one, Ahrends said, when it comes to mapping land conversion for agriculture, the lion’s share of the attention goes to commodities such as palm oil and soy, often leaving rubber overlooked. While there have been some attempts to map rubber cultivation in individual countries, there’s no comprehensive map for the whole of Southeast Asia, where almost 90% of the world’s natural rubber is produced.

Mapping rubber cultivation is tricky for other reasons too. Rubber plantations are often managed by smallholders on lands that can be hard to track and identify. Moreover, with their row after row of trees yielding a near-uniform canopy, rubber plantations can often look like natural forests on satellite images. “It might surprise people, but it is still quite hard to map cash crops because it is not easy to differentiate between the different species of vegetation from space,” Ahrends said.

To get around this hurdle, Ahrends and her team used a combination of remote-sensing technology and fieldwork to understand the extent of deforestation caused by rubber plantations in Southeast Asia.

They used data from Sentinel-2, an Earth-observation mission from the European Space Agency, to map the rubber plantations. The mission’s twin satellites pass over a given area relatively frequently, allowing the team to differentiate rubber plantations from other trees. “Rubber has a characteristic leaf drop and regain pattern which occurs over a relatively short time window of just four months,” Ahrends said. “We used the satellite imagery to identify all tree cover that drops the leaves and then regained them relatively rapidly.”

Once they’d mapped the rubber plantations, the team overlaid maps with deforestation imagery from NASA’s Landsat program. This allowed them to pinpoint areas where healthy vegetation was burned to the ground and where new regrowth — indicating plantations as shown in the rubber maps — takes place. Thanks to collaborations with partners, the team got access to a lot of ground data for verification.

The work wasn’t without its challenges.

Cloud cover can run interference, obscuring satellite images and making it hard for scientists to get a clear understanding of the situation on the ground. Additionally, Ahrends said, gathering the data using remote sensing was the easy part; the subsequent ground truthing and corroboration was more challenging and time-consuming.

“There is only so much tech can do,” she said. “It’s having the contextual ground data that allows you to identify the spectral characteristics of the crop in the first place and then to ground truth what you’ve done to see whether the maps are any good or not — that’s the time-consuming element.”

Ahrends called for more efforts to get citizen scientists involved to fill this knowledge gap. “At the end of the day, a pixel looks green from space when there are trees in it, and what species they exactly are is still very hard to say from remote sensing,” she said.

Ahrends said she hoped the study would serve as a wake-up call and prompt action to regulate a universal certification process to ensure that rubber is procured sustainably.

“We’re not advocating to demonize rubber, because small-scale farmer livelihoods depend on the crop and synthetic alternatives produced from fossil fuels are more environmentally harmful,” she said. “It is actually a good crop that can provide a sustainable income to farmers if it’s planted and managed sustainably.”

Banner image: Rubber latex collecting into a container in a rubber plantation in Thailand. Image by Eleanor Warren-Thomas via Flickr (CC BY-NC-ND 2.0).

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Citations:

Wang, Y., Hollingsworth, P. M., Zhai, D., West, C. D., Green, J. M., Chen, H., … Ahrends, A. (2023). High-resolution maps show that rubber causes substantial deforestation. Nature, 623(7986), 340-346. doi:10.1038/s41586-023-06642-z

Warren‐Thomas, E., Ahrends, A., Wang, Y., Wang, M. M., & Jones, J. P. (2023). Rubber’s inclusion in zero‐deforestation legislation is necessary but not sufficient to reduce impacts on biodiversity. Conservation Letters, 16(5).