- Shifting cultivation is expanding into intact forest frontiers in Laos, triggering a spike in associated carbon emissions, according to a new study based on satellite data.
- As the dominant land use type in Laos, shifting cultivation has affected roughly one-third of the country’s total land area over the past three decades, the study says.
- The study also highlights how fallow land, a vital carbon store in Laos, is increasingly undermined by farming practices characterized by shorter fallow periods.
- The authors say their data can be used by policymakers to design programs that support more sustainable forms of shifting cultivation. Experts urge that such interventions sensitively consider why remote communities might be forced to transition away from traditional, subsistence-based farming toward intensified systems.
As the government of Laos continues to prioritize a hydropower-heavy agenda to generate export revenues while striving toward greenhouse gas emissions reduction targets, it may be overlooking soaring carbon emissions from intact forest loss right under its nose.
A new study published in Environmental Research Letters indicates a recent expansion and intensification of shifting cultivation in Laos, resulting in direct loss of forests, degradation of important carbon sink ecosystems, and substantial increases in carbon emissions.
The findings build on research published earlier this year that used satellite data to map the extent of shifting cultivation in Laos between 1991 and 2020, revealing that it affected roughly one-third of the total land area of Laos over the past three decades.
Shifting cultivation is a type of rotational farming typically practiced by small-scale subsistence farmers. Also known as swidden agriculture, it involves clearing and burning a plot of land to fertilize the soil for growing crops. After a short period of cultivation, the land is left fallow and the farmer moves on to a new patch, affording the vegetation time to regenerate.
“Shifting cultivation is an important land use in the tropics, but it has a number of negative consequences like carbon emissions, biodiversity loss and it can even spread wildfire if it’s not controlled very well,” Shijuan Chen, a postdoctoral associate at Yale University and lead author of both studies, told Mongabay.
Laos is home to some of mainland Southeast Asia’s last remaining expanses of intact tropical forest, including important montane forests in the Annamite mountain range where scientists have described species such as the Annamite striped rabbit (Nesolagus timminsi), the saola ox (Pseudoryx nghetinhensis) and the large-antlered muntjac (Muntiacus vuquangensis) that occur nowhere else on the planet. The latest forestry strategy of Laos estimated that forest covered 62% of the country in 2005, with aims to achieve 70% forest cover by 2025.
To calculate the area of land under shifting cultivation and its associated carbon emissions, Chen and her colleagues used satellite imagery with a resolution of 30 meters (100 feet) from the Landsat platform to map land uses across Laos each year between 1991 and 2020. Next, they layered lidar imaging data from the Global Ecosystem Dynamics Investigation (GEDI) program over the shifting cultivation distribution maps to estimate aboveground biomass, which enabled them to calculate net carbon emissions.
Chen said calculating the fine-scale balance between carbon emissions and carbon sequestration was a particular challenge. On the one hand, clearance of land releases carbon as trees and other biomass are razed to the ground and burnt; however, during the fallow period, carbon is sequestered back into the site as vegetation regenerates.
While shifting cultivation has a poor reputation for being a source of forest degradation and deforestation in many tropical countries, including Laos, studies show that in some cases, it can enhance species richness in tropical forests. A 2023 study in Belize, for instance, found that Indigenous practices of shifting agriculture created patchworks of habitats leading to localized increases in rainforest plant diversity.
In Laos, however, it seems the expansion and intensity of shifting agriculture “is becoming less sustainable,” according to Chen. The team found that the area of new land being cleared each year to make way for shifting cultivation declined between 2001 and 2015, with an accompanying downward trend in associated carbon emissions. But since 2016, new areas of shifting cultivation have expanded significantly into intact forests, with accompanying elevated levels of carbon emissions.
Given the extent of shifting agriculture in Laos, fallow land is an important carbon sink, the study says. But the team found that land that was once typically left fallow for an average of 6.5 years between cultivations is now being resown as frequently as every two years — an intensity that doesn’t afford vegetation sufficient time to recover in terms of biomass, ecosystem services and species diversity.
Alan Ziegler, a professor working on human-environment systems at Maejo University in Thailand, who was not involved in the study, said the results are broadly consistent with what other researchers have observed in montane forest frontiers in the wider region. He told Mongabay that although remote-sensing data is very useful and increasingly accurate, it’s difficult to assess the full implications of satellite-based data without information from the field. “One really needs to be on the ground to understand the form of agriculture that is taking place,” Ziegler told Mongabay in an email.
Without field observations, Ziegler cautioned against attributing forest loss detected anywhere in the region solely to “traditional” shifting cultivation, such as swidden agriculture practiced by subsistence farmers, when it could include more intensive smallholder agricultural practices that he said should be distinguished.
Distinguishing between various agricultural practices is vital because “many objective observers think that traditional forms of shifting agriculture (swidden agriculture) are not destructive when sufficient fallow periods are maintained, and particularly when full recovery of secondary forests is achieved,” Zielger said. “However, when these fire-assisted systems become more permanent and involve the cultivation of cash crops, negative impacts increase.”
Ziegler cited the example of Thailand’s northern Nan province, where vast tracts of upland forest have been converted to agriculture in recent decades. Researchers found that what initially looked like expansion of shifting cultivation from satellite data were, in fact, “boom crops” including rubber and corn, largely driven by regional and international markets. “It’s really easy to imagine how forest loss and prices of lucrative cash crops might correlate in some areas,” Ziegler said, adding that oil palm is another such driver of forest loss in lowland parts of Southeast Asia.
Regardless of whether similar patterns are behind the land-use shifts recorded in Laos, Ziegler said it’s important to acknowledge why remote communities might be forced to transition away from traditional, subsistence-based farming toward intensified systems growing cash crops.
“Things were tough in the region following COVID-19,” Ziegler said. “The price of many necessities has increased greatly, and many rural people have little access to cash at a time when money is increasingly needed, but wages and profits from farming have not kept pace.” Some of the patterns of agricultural expansion and intensification detected in Laos could be people returning to farming to tide them through the harsh economic period, he said. “These days it is hard to only practice subsistence living, even in remote areas.”
Chen said she would next like to incorporate measures of belowground biomass into the analyses and work with social scientists to understand what’s causing the recent expansion of shifting agriculture in Laos. For now, though, she said the new data on landscape pressures and associated carbon emissions can help policymakers to support remote communities who depend on shifting cultivation to live as sustainably as possible.
Carolyn Cowan is a staff writer for Mongabay. Follow her on 𝕏, @CarolynCowan11.
Banner image: Small-scale shifting agriculture creates a patchwork of crops and vegetation regrowth among mature tropical forest. Image by Rhett A. Butler for Mongabay.
See related story:
Forest loss in mountains of Southeast Asia accelerates at ‘shocking’ pace
Citations:
Chen, S., Woodcock, C. E., Saphangthong, T., & Olofsson, P. (2023). Satellite data reveals a recent increase in shifting cultivation and associated carbon emissions in Laos. Environmental Research Letters, 18(11), 114012. doi:10.1088/1748-9326/acffdd
Chen, S., Olofsson, P., Saphangthong, T., & Woodcock, C. E. (2023). Monitoring shifting cultivation in Laos with Landsat time series. Remote Sensing of Environment, 288, 113507. doi:10.1016/j.rse.2023.113507
Feng, Y., Ziegler, A. D., Elsen, P. R., Liu, Y., He, X., Spracklen, D. V., … Zeng, Z. (2021). Upward expansion and acceleration of forest clearance in the mountains of Southeast Asia. Nature Sustainability, 4(10), 892-899. doi:10.1038/s41893-021-00738-y
Downey, S. S., Walker, M., Moschler, J., Penados, F., Peterman, W., Pop, J., … Song, S. (2023). An intermediate level of disturbance with customary agricultural practices increases species diversity in Maya community forests in Belize. Communications Earth & Environment, 4(1). doi:10.1038/s43247-023-01089-6
Ziegler, A. D., Phelps, J., Yuen, J. Q., Webb, E. L., Lawrence, D., Fox, J. M., … Koh, L. P. (2012). Carbon outcomes of major land‐cover transitions in SE Asia: Great uncertainties and REDD+ policy implications. Global Change Biology, 18(10), 3087-3099. doi:10.1111/j.1365-2486.2012.02747.x
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