Conservation news

Plantations can produce more palm oil if they keep riverbanks forested

Oil palm plantations are the biggest source of agriculture-related deforestation in Southeast Asia. Researchers estimate that at least 95,000 square kilometers of land have been converted to oil palm plantations in Malaysia and Indonesia since 1990, with Indonesia incentivized to double its palm oil production capacity by 2030.

While many plantations are developed on land that has already been logged or degraded, over 50 percent have been developed at the expense of tropical forests. Conversion of tropical forests to oil palm plantations negatively impacts both the global climate and local wildlife by destroying natural carbon stores and leaving rainforest habitat increasingly fragmented.

Areas of protected forest remain, but these smaller patches cannot support the full diversity of the region’s wildlife in isolation. Some conservationists say one possible solution to this problem would be to preserve intact forest corridors connecting protected areas, allowing a higher percentage of the region’s biodiversity to stay intact.

Endangered Bornean orangutans (Pongo pygmaeus) are suffering from the effects of deforestation and consequential habitat fragmentation throughout their native range.

The riparian forests that hug the banks of meandering tropical rivers are perfect natural candidates for these pathways. They play a crucial role in the migration of species like the endangered Bornean pygmy elephant (Elephas maximus boreensis) and provide nesting grounds for primates like the endangered proboscis monkey (Nasalis larvatus). Currently, however, a large percent of floodplain forests in Southeast Asia are unprotected and open to development.

While the conservation benefits of preserving riparian forest corridors are clear, conventional wisdom holds that there is little economic incentive for plantation developers to leave intact forest on fertile — and potentially profitable — river floodplains. However, a new paper released in the journal Earth’s Future argues that economic and conservation objectives might be more closely aligned than previously thought.

Endangered proboscis monkeys (Nasalis larvatus) are endemic to Borneo and use riparian forests to nest by the river at night.

A team of researchers from Cardiff University and Danau Girang Field Centre have found that keeping a buffer of trees along meandering tropical riverbanks doesn’t just help out local wildlife — it ensures that plantations do not lose valuable crops to riverbank erosion.

“Preserving tropical forest buffers along the margins of large meandering rivers can enhance the profitability of floodplain plantations while maintaining conservation benefits by reducing the area of land lost to the river through bank erosion,” said lead author Alexander Horton of Cardiff University.

Horton and his colleagues found that rather than hurting profits, leaving at least 10 meters of riparian forest between the riverbank and oil palm crop can actually maximize yield and prove more profitable than planting oil palm right up to the riverbank.

To model the erosion prevention benefits of a riparian forest buffer, the team looked at a 210-kilometer stretch of the Lower Kinabatangan River, located in Sabah, a major oil palm-growing state in Malaysian Borneo. Since 1990, the majority of the floodplain forests along the Kinabatangan have been converted to oil palm plantations, and 36 percent of the riparian forests in the study area are currently unprotected.

Traditionally, floodplain oil palm plantations (like the one pictured above) remove riparian forest during conversion. This can have detrimental effects on local wildlife and the health of rivers, and leaves plantations vulnerable to erosion and flooding. Photo courtesy of HUTAN

The researchers modeled bank erosion rates at 25-year intervals — the length of an average oil palm crop growing cycle — for up to 100 years. They also compared potential palm oil yields given ten different forest buffer widths between 10 and 100 meters.

The team found that a larger buffer has a bigger payoff in the long term, but a forest buffer of 10 to 20 meters could maximize yields even within a ten-year period. Already within that time, a narrow forest buffer’s protective benefits offset the loss of cultivated land by ensuring young palms near the river are not lost to erosion before they begin generating revenue. Meanwhile, buffers of 30 meters or more could maximize yields in the long term.

“We find that riparian buffers of an order of tens of meters may enhance the long-term viability of floodplain plantations. Which means that accounting for geomorphic contributions to ecosystem services may help align palm oil industry goals with environmental conservation,” said study coauthor Benoit Goossens, director of Cardiff University’s Danau Girang Field Institute.

The authors also note that the erosion prevention they projected for riparian forests are based on conservative calculations, meaning that preserving a riparian forest buffer could be even more economically beneficial than their estimates indicate.

“We were very conservative with our assumptions, always erring on the side of caution, so we were surprised that the timeframes until the economic return were still so short,” Horton said. “If we could properly account for all of the ways in which leaving riparian buffers benefit the local population, then we might see a real shift in attitude.”

Riparian buffers like this one can protect oil palm plantations from losing land to riverbank erosion, increasing yield even in the short term. Photo courtesy of HUTAN

For instance, forest buffers can decrease the buildup of sediment in the river over time, which could increase the river’s migration rates. Riparian forests also mitigate the impacts of flooding, which the researchers say could have an even greater effect on short-term profits.

They also note that while their research focused on the erosion prevention benefits to oil palm plantations on the Kinabatangan River, their approach is generalized enough that their findings likely extend to other regions, as well as other forms of agriculture adjacent to forested tropical floodplains.

“We hope that this work will highlight the benefit tropical forests can offer to floodplain plantations, and encourage the preservation and even restoration of these sensitive forests,” Horton said.

 

 

Citation: Horton, A. J., Lazarus, E. D., Hales, T. C., Constantine, J. A., Bruford, M. W., & Goossens, B. (2018). Can riparian forest buffers increase yields from oil palm plantations? Earth’s Future, 6. https://doi.org/10.1029/2018EF000874

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