RUBBER TREE EXPANSION IN FOREST RESERVE AND PADDY FIELD ACROSS THE GREATER MEKONG SUB-REGION, NORTHEAST THAILAND BASED ON REMOTELY SENSED IMAGERY

摘要

Agricultural land use of the Greater Mekong Sub-region (GMS) is being rapidly reshaped by expansion of rubber tree plantation. This occurrence, which has been progressed at an increasing rate in the last three decades, has had consequences for surface water hydrology, degraded ecosystems and loss of paddy land, and has accelerated the processes of drought and flooding. The ensuing scarcity of land has led to the plantation encroachment on legal forest reserve and paddy land marginally unsuitable for rubber tree. The study aims to address the encroachment areas of the rubber tree plantation on the forest reserve of government land and on the paddy field. The study area, a portion of northeast Thailand in the GMS, covers an area of approximately 1.7 million ha and is characterized by gently undulating topography .The methodology procedure comprised an analysis of imagery for land cover/land use(LCLU),a comparison of LCLU changes and spatial and quantitative identification of the expansion of the rubber tree plantation. The 2002 aerial orthophotography and 2011 THAICHOTE imagery were used to derive LCLU on which the changes and expansion areas were analyzed. Spatial and quantitative information on the rubber tree expansion areas and its change rate was derived from an overlay of the conservation forest (CF) and paddy field layers on the 2002 and 2011 LCLU maps. The total plantation area increased from 42,411.75 ha in 2002 to 288,550 ha in 2011 with its average expansion rate of 27,348.694 ha/annum (155.08%). Of the total plantation area, the plantation encroachment on the legal forest reserve shared about 2.23 % (947.60 ha) in 2002 and 4.77% (10,835.17 ha) in 2011. Moreover, the expansion in the paddy land, which is marginally suitable for rubber tree, covered 3,424.72 ha in 2002 and 42,231.35 ha in 2011, representing 8.07% and 14.63 % of the plantation areas respectively. Our study provided geo-spatial information on the plantation distribution and the expansion areas in the forest reserve and the paddy land as well.