Hypothesis 1 More recently developed paddy fields have
higher density than older fields.
In order to examine if the density of trees in paddy fields
is related to the history of land development, a set of maps
showing land use, ‘‘INDOCHINA and Thailand 1:250,000
Series L509,’’ was obtained from the University of Texas
Libraries’ website (http://www.lib.utexas.edu/maps/ams/
indochinaandthailand) on 1 April, 2011. These 1:250,000
scale maps were compiled by US Army Map Service based
on 1:50,000 maps showing land uses such as woodland and
rice paddies that had been compiled by the Thai Royal
Survey Department before the 1950s (Table 1)