Eighteen
sheets covering Northeast Thailand were utilized in this
survey of which five sheets were compiled in 1954, three in
1955, nine in 1958, and one in 1962. Because we cannot
assign precise dates to the land use data, we can only be
certain that it represents land use sometime before the
1950s. Using GIS, the map of tree densities compiled from
the IKONOs images was overlaid on these maps of past
land use. Based on the land use categories displayed on the
maps, grid cells were classified into the newer paddy field
group, for which all cell areas were categorized as woodland (69 grid cells), and the older paddy field group, for
which parts of cell areas were categorized as rice paddy
(116 grid cells). Eighteen grid cells including non-classified land were excluded from the analysis. Any paddy
fields now found in cells in the newer paddy field group
would have been developed after the maps were made so
can be considered as new fields. Since cells in the older
paddy field group already contained paddy fields by the
early 1950s, any fields we found inside these cells can be
considered as old paddies. The statistical significance of
differences among the groups was tested with the two-sided
Mann–Whitney U test.