- Oil palms growing in rewetted peatlands show no decline in palm fruit yields compared to those in drained peatlands, a new study shows.
- This debunks the long-held thinking in the palm oil industry that draining the carbon-rich peat soil is necessary to maintain yields on peatlands.
- Instead, rewetting peatlands should have net positive effects for smallholders by reducing the risk of fires that can damage property, plantations and human health.
- The study also finds that conserving peatland forests supports bird biodiversity, as a richer variety of bird life is found in peat forests than in adjacent oil palm plantations.
JAKARTA — For decades, oil palm farmers in Indonesia have drained — and destroyed — tropical peatlands on the basis that the crop doesn’t grow well in the boggy soil. But now, a new study shows that oil palms grown in rewetted peatlands show no drop in productivity.
The findings shore up environmental activists’ case that oil palms can be farmed more sustainably on peatlands by rewetting the land, thereby conserving biodiversity and reducing the risk of fires.
“What this new study shows is that retaining more water in oil palm farms to reduce fire risk seems to have no effect on yields, which is good news for farmers,” said study lead author Eleanor Warren-Thomas, a conservation scientist at Bangor University in the U.K. “In contrast to the concerns of some plantations, retaining water levels close to the surface” — within 40 centimeters, or 16 inches — “still enables oil palm cultivation.”
Udin, a farmer who collaborated on the study, said that “Even if the farm flooded for a few days, the yield is not decreased.”
These findings indicate that it’s possible to shift away from an agricultural system that depends on draining peatland into one that’s more sustainable and peat-friendly, which reduces the risk of fires and land subsidence.
“In the long term, withdrawal of drainage-dependent agriculture from peatland is necessary to avoid carbon emissions and land loss to subsidence, with forest restoration or flood-tolerant agriculture the sustainable alternatives,” the study says.
It also suggests the results are scalable to much larger plantations: “[O]ur overall conclusion would qualitatively be the same: that water tables had minimal influence on oil palm yields … on oil palm farms in our study system,” the study says.
History of peat draining
Indonesia is the world’s biggest producer of palm oil, much of which is planted on drained peatlands on the islands of Sumatra and Borneo. The conventional wisdom in the industry is that drainage is necessary because water-logged soil reduces palm fruit production.
But when peatlands are drained for cultivation, the perennially moist and carbon-rich peat layer dries out, becoming highly prone to fires, especially during the dry season. Peat draining has turned some regions in Indonesia, especially in Sumatra, into hotspots for peat fires, which release huge amounts of carbon dioxide into the atmosphere and generate a health-threatening toxic haze.
To tackle the recurring fires, the Indonesian government has implemented a number of policies, such as restoring degraded peatlands across the country by rewetting them. This process involves blocking drainage canals, but has also raised concerns over the livelihood impact to smallholder farmers, Warren-Thomas said.
“Indonesia has been very successful in reducing deforestation and considerable effort has gone into peat restoration to avoid fires,” she said. “But one of the big challenges is the trade-off between livelihoods of owners of small farms and ensuring biodiversity in these areas.”
The study thus sought to confirm whether the farmers’ concerns — that their palm fruit yields would decline if their drained-peat plots were rewetted — were warranted. It looked at how variations in water table depth — essentially, the difference between drained and undrained peatlands — affect oil palm yields on smallholder farms in Sumatra’s Jambi province.
Warren-Thomas and her colleagues also compared bird diversity in oil palm farms with a nearby protected peat forest fragment to understand changes in diversity and ecological function following the conversion of peat swamp forest to plantation, and to assess the importance of conserving forest fragments for future restoration initiatives.
They established 62 sampling plots: 41 of them in oil palm plantations and 21 in an adjacent area of protected forest to use as a reference site to indicate water table variation in the landscape under minimal drainage.
While they found that oil palm yields varied considerably among the farms, from 4.5 to 19.2 tons per hectare per year (or an average of 11 tons per hectare per year), the water table wasn’t the determining factor.
“[Y]ields were not detectably related to drainage within the measured range of drainage depths, nor to any other measured variables representing management strategies, oil palm age, tree health chemical applications or by site,” the study says.
The researchers therefore concluded that the variation in yields was driven by factors not examined in the study, and that rewetting peatland doesn’t necessarily reduce yields.
On the contrary, the study found that rewetting should have net positive effects for smallholders by reducing the risk of fires that can damage property, plantations and human health.
Bird and plant diversity
Another bonus was that wetter farms had more complex ground vegetation. But this didn’t translate into an increase in the bird diversity, the researchers said.
Overall, bird species diversity and abundance were 50% lower on oil palm farms than in the neighboring peat swamp forest, with only 48 species found on the farms compared to 90 recorded in the forest. The latter birds also tended to be larger, indicating they play different ecological roles in the forest ecosystem.
“These unique birds can also act as seed dispersers — crucial if in the longer term forest restoration becomes an option,” Warren-Thomas said.
The study found 35 conservation-priority bird species in the forest, and only three on the oil palm farms. No forest-dependent bird species were found on the farms.
These findings emphasize the importance of not just rewetting converted peatland, but also conserving peat forests to support biodiversity, the researchers said.
“The forest fragment retained large-bodied frugivorous bird species that are important for future peatland restoration potential, and for retaining genetic diversity and gene flow among isolated forest fragments,” the study says. “However, the forest fragment is vulnerable to drainage and fires in surrounding cultivated land.”
The researchers noted that their findings of no correlation between vegetation complexity and bird richness on oil palm farms were at odds with other research emphasizing the importance of understory vegetation for greater bird diversity in plantations. They attributed this lack of consensus to differences in oil palm management across farms in different studies.
“For example, in Peninsular Malaysia, a positive effect of understorey vegetation on bird richness was seen only in polyculture oil palm farms, not in monocultures,” the study says. “In our study landscape, the predominance of monocultural oil palm may result in fewer bird species capable of responding to local variation in understorey vegetation.”
Scaling up the study
The researchers noted that on the point of biodiversity, they only looked at birds, and not insects or mammals or reptiles. These other species might be influenced by variation in local vegetation, with understory vegetation, or lack thereof, known to affect mammal occurrence on oil palm farms in Colombia.
“Therefore, the impact of peatland re-wetting on other taxa will differ from the responses of birds, and our results cannot be generalised to all biodiversity,” the study says.
Another caveat is that all the sites surveyed by the researchers were relatively shallowly drained in the year of the study. As a result, the researchers couldn’t draw conclusions about the effect of deeper drainage on yields or biodiversity.
The researchers also noted that they were unable to account for the potential time lag, of 20 to 30 months, between management or weather effects on oil palms and changes in yield. This is because the researchers analyzed self-reported yields and data from questionnaires in the study; logistical constraints meant they couldn’t take measurements over time.
The study also only focused on oil palm yields and bird diversity on smallholder plantations, but not industrial plantations. Since management, oil palm age, water tables and yields are likely to be more closely controlled on industrial plantations, studies of the latter would be able to better examine potential trade-offs, the researchers said.
“Comparisons of yield-drainage relationships between smallholders and industrial scale oil palm would be very informative, especially in the context of sustainability initiatives such as guidance from the Roundtable on Sustainable Oil Palm,” the study says.
To make studies of industrial plantations possible, it’s important for companies to be more transparent, Warren-Thomas added.
“One of the conclusions of the study is that larger-scale industrial farming organizations would be able to help further studies in this area, if they are able to publish their data and share their knowledge to inform sustainable oil palm production strategies,” she said.
The study also calls for continued monitoring of yield outcomes on the studied farms in the coming months as part of wider restoration planning.
“This information will be vital for helping to close yield gaps, produce oil palm to meet growing demands and improve smallholder livelihoods, without increasing plantation area,” the study says. “However, increased yields on farms may not result in avoided deforestation unless there is accompanying forest governance and enforcement of protection, but higher yields are required if production is to match increasing demand without further deforestation.”
Warren‐Thomas, E., Agus, F., Akbar, P. G., Crowson, M., Hamer, K. C., Hariyadi, B., … Hill, J. K. (2022). No evidence for trade‐offs between bird diversity, yield and water table depth on oil palm smallholdings: Implications for tropical peatland landscape restoration. Journal of Applied Ecology, 59(5), 1231-1247. doi:10.1111/1365-2664.14135
Banner image: Cleared peatland for agriculture in Central Kalimantan. Image by Anna Finke/CIFOR via Flickr (CC BY-NC-ND 2.0).
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