Changing land use patterns in northern Thailand: Effects of agricultural practices in Mae Chaem

This dissertation presents the impacts of historical land use on landscape patterns and dynamics in three ethnic Karen villages in the district of Mae Chaem, Chiang Mai province, Northern Thailand. In Khun Mae Yot, farmers have retained a traditional long-fallow shifting cultivation system with a 10–12 year fallow period. In Mae Hae Tai, the length of fallow has been shortened to 5–6 years. In Yang Sarn, shifting cultivation was replaced with permanent agriculture in the mid-1980s. Vegetation surveys were carried out to examine variation in floristic and structural components of secondary vegetation and forest land cover types contained within each landscape. In general, number of trees and basal area increase with fallow age, with a slight drop of the number of trees in residual original forest plots. Tree species diversity is lowest in the younger fallow stands and increases as the stands get older, with a slight decrease in mature forest stands. An exception is Yang Sarn's disturbed forest, which contained only a few large trees. Overall, plots in Khun Mae Yot have the highest species diversity, while plots in Yang Sarn have the lowest diversity and those in Mae Hae Tai contain intermediate values. Even though fallow plots had attained similar levels of basal area and species richness at some ages, their species composition remained distinct from that of the representative stands of residual original forest. Landscape analysis of time-series aerial photographs taken at intervals between 1954 and 1996 allows investigation of effects of different histories of agriculture on landscape dynamics. The landscape of Khun Mae Yot showed the least changes in landscape proportions and patterns. Land cover classes appeared to be almost constant throughout the 1954–1996 period, but land cover patches show dynamic interchanges. The reduction of fallow length in Mae Hae Tai resulted in increasing dominance of secondary vegetation as well as the disappearance of forest by 1996. The landscape thus became more homogeneous. The landscape of Yang Sarn showed a substantial increase in agricultural area at the expense of secondary vegetation and forest.