Spatial identification by satellite imagery of the crop–fallow rotation cycle in northern Laos

Abstract

In the mountainous regions of northern Laos, shifting cultivation, or slash-andburn agriculture, is widely practiced. However, the crop-fallow rotation cycle is becoming shorter owing to forest conservation policies and population pressure, causing loss of productivity that deleteriously affects farmers' livelihoods in the region. To investigate regional land use conditions, we have developed a method of identifying the crop-fallow rotation cycle from Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper+ (ETM+) data. We assessed the impact of the identified cycle on plant production measured by Normalized Difference Vegetation Index (NDVI). The study site was an area in Luang Prabang Province. Using eight TM and ETM+ images acquired annually from 1995 to 2003, except for 1998, when cloud-free data were not collected, we classified land use in each year as crop or fallow by the presence of vegetation in the late dry season. Conformity with fallow age determined by field investigation was 69.1%. The cultivation frequency from 1995 to 2002 showed that 77,000 ha (17.3% of the study site) had not been used for cropping during the period, but 41,000 ha (9.2%) had been used every year. Of the study site, 129,000 ha (29.1%) was cultivated one or two times, 83,000 ha (18.7%) was three or four times, and 54,000 ha (12.2%) was five or six times. The NDVI of crops in November did not provide sufficient evidence to prove the assumption that a longer fallow period would result in better crop yields. Instead, the regeneration of fallow vegetation was Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. evidenced by the higher NDVI values after longer fallow. More than 8 years would be needed to reach the same NDVI as forest. From the produced maps indicating fallow age and cultivation frequency, we found that areas with high potential for regeneration decreased as cultivation frequency increased. Areas near rivers were intensively used, and fallow length was accordingly short. Low-potential areas were found in the western basin of the Mekong River. This spatial information can be used to detect areas where biomass productivity is at high risk of deteriorating.

Rubber Plantation Expansion Related Land Use Change along the Laos-China Border Region

“…Research performed mainly focused on changes of the structure and type conversion, while we analyzed LUCC from the perspectives of structure, type conversion and spatial pattern [23,33]. We paid more attention to the changes of swidden land and rubber plantation, which were affected significantly by human activities [24,31,32,47,48]. In light of the quality of Landsat images and limited field samples, accuracy assessment of land use and land cover classification maps should be improved further, especially for the grassland and tea garden.…”

A Texture-Based Land Cover Classification for the Delineation of a Shifting Cultivation Landscape in the Lao PDR Using Landscape Metrics

“…Such a delineation or assessments of the crop-fallow rotation cycle are typically either based on an analysis of a time series of satellite imagery or information on the land use [2,3,9,11,12].…”

“…To detect these spatio-temporal patterns of shifting cultivation using remote sensing, most studies have analyzed time series of satellite images [3,[8][9][10][11]. By classifying the cultivated areas and the vegetated areas of each image of the time series and performing a post-classification comparison, the plots under shifting cultivation and their crop-fallow rotation cycles can be assessed [3].…”

Managing water in rainfed agriculture in the Greater Mekong Subregion

“…A shortening of the fallow period and an extension of the cropping period has been observed in shifting cultivation in most areas as population density has increased. This has reduced the capacity of the land to recover during fallow periods, due to a decline in soil fertility, an increase in weed pressure, and, in some cases, very high rates of soil erosion (Yamamoto et al 2009). Traditional swidden systems have low-to-moderate overall soil loss (high in cultivated years, low in fallow years) but decreasing fallow periods, and changing cropping systems can result in very serious erosion.…”