关键词: 刀耕火种农业, 时空变化, 轮歇周期, 利用频率, 植被恢复, 老挝北部

Abstract:

Swidden agriculture is an age-old, prevailing but controversial farming practice in Montane Mainland Southeast Asia (MMSEA). In the uplands of northern Laos, swidden agriculture has become the predominant land use type for centuries. The swidden system has undergone dramatic transformations since the mid-1990s. The debate on the change of swidden cultivation is linked to global critical issues of land use/cover change, biodiversity and climate change. Since the implementation of Reducing Emissions from Deforestation and forest Degradation (REDD) by the United Nations, an increasing attention has been given to swidden agriculture in the humid tropics nationally and internationally. However, very little is known or reported about the explicit spatial information of swidden agriculture and the consequences of the transitions at macroscopic scale. For the purpose of understanding the spatial and temporal dynamics of swidden system, the intensity of swidden use and fallow forest recovery in northern Laos, in this study, the swidden agriculture in 1990, 2002, and 2011 were mapped and delineated with Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper plus (ETM+) imagery (30 m) with a decision tree classification method, followed by the analysis of spatio-temporal changes of swidden agriculture. Then, annual successive TM/ETM+ images during the period 2000-2010 were used to delineate the dynamics of burning phase and cropping phase. Subsequently, the burned pixels derived in 2000 were compared with those in the following years (2001-2011) under ArcGIS 10.0 to investigate the temporal development, land use frequency and swidden cycle with time-series Landsat-based NDVI data. Finally, as the swidden cycle changed from 1 to 11 years, the fallow vegetation recovery process was studied. The results showed that: (1) From 1990-2011, the area of swidden agriculture increased by 54.98%, from 153,800 to 238,400 ha. The increased swidden cultivation were mainly found in Luang Prabang and southern Bokeo; while the decreased parts were mainly in Phongsali. (2) The swidden agriculture mainly increased at the elevations of 500-800 m, 300-500 m and 800-1000 m and on the slopes of 10°-20° and 20°-30°. More than 80% of swidden farming land was transformed from forests. (3) During the period 2000-2011, the frequency of swidden use in northern Laos was about 2 or 3 times. The intervals of any two swidden use phases ranged from 1 to 7 years. In comparison with swidden cycles and the related proportion of swidden farming in the years of 2000, 2003 and 2007, swidden cycles in most parts were shortened. (4) There was a significant correlation between fallow vegetation recovery and swidden cycle, with a correlation coefficient of 0.9698. The NDVI of regenerated vegetation could be equal to the average NDVI value of forest when the swidden cycle reaches 10 years.

Key words: swidden agriculture, spatio-temporal changes, swidden cycle, frequency of swidden use, fallow vegetation recovery, Landsat, Laos