Reduction in woody plant diversity in paddy field landscapes during agricultural intensification in northeast Thailand

Trees in paddy fields characterize the landscape of plain areas in mainland Southeast Asia. Although they play an important role in providing subsistence materials to local communities and in maintaining biodiversity, their distribution patterns are affected during agricultural intensification. In this study, we compared the density and species diversity of trees in two types of paddy fields (i.e., with and without land consolidation) to examine the effects of agricultural intensification on the woody plant community. Aerial photographs and satellite images were used to record changes in land use and tree-unit density from 1975 to 2014 at 18 target sites in three different rural landscapes. Field surveys were conducted in 2015 to investigate the total individual trees, species richness, and individual tree density. Tree species diversity was low at the local scale and varied greatly among sites, resulting in greater diversity at the landscape level. Tree species composition changed, with an increase in the number of ruderal and planted trees. During 1975-2014, the paddy plot size expanded three times due to land consolidation. As plot sizes increased, the density and species richness of remnant trees in the fields decreased, whereas planted trees on the levees were unaffected. Our results suggest that to enhance biodiversity in paddy fields, there should be a focus on improving the quality of trees planted on the levees. Smartly incorporation of various tree species onto paddy levees, together with appropriate guidelines for management of a paddy field-based agroforestry would be effective for preserving landscape sustainability.