Monitoring shifting cultivation in Laos with Landsat time series

Shifting cultivation is an agricultural practice in which plots of land are cultivated temporarily, then abandoned, and vegetation is allowed to regenerate during fallow periods. Shifting cultivation is usually associated with cutting and burning forests and thus it is an important driver of forest disturbance in the tropics. However, studies of shifting cultivation are limited, and current area estimates of shifting cultivation are highly uncertain. Although Southeast Asia is a hotspot of shifting cultivation, there are no national maps of shifting cultivation in Southeast Asia at moderate or high resolution (less than or equal to 30 m). Monitoring shifting cultivation is challenging because it is highly dynamic, small-scale and results in complex post-disturbance landscapes. In this study, we monitored shifting cultivation using Landsat time series on Google Earth Engine for the entire country of Laos from 1991 to 2020. First, CCDC-SMA (Continuous Change Detection and Classification - Spectral Mixture Analysis) was used to detect forest disturbances. Then, these disturbances were attributed by combining time series analysis, object-based image analysis (OBIA), and post-disturbance land cover classification. Forest disturbances were assigned to Shifting cultivation, New plantation, Deforestation, Severe Drought, and Subtle Disturbance annually from 1991 to 2020 at a 30-m resolution. The major forest disturbances in 1991–2020 were mapped with an overall accuracy of 85%. Shifting cultivation is mapped with a producer's accuracy of 88% and a user's accuracy of 80%. The margin of error of the sampling-based area estimates of Shifting cultivation is 5.9%. Shifting cultivation is the main land use in Laos, accounting for 32.9% ± 1.9% of Laos over the past 30 years. To study changes in shifting cultivation over time, the area of shifting cultivation was estimated at 5-year intervals between 1991 and 2020 with all margins of error <17%. Results show that the area of slash-and-burn activities in Laos increased in 2015–2020. Our study provides an effective approach for monitoring shifting cultivation, which can be potentially applied into other regions. Our results not only provide valuable information for land management in Laos, but also can support analysis of spatial-temporal patterns of shifting cultivation and estimation of carbon emissions associated with shifting cultivation for REDD+ reporting.