Results and Discussion
Spatial Variations in the Density of Trees in Paddy
Fields in the Northeastern Region
Although the paddy fields in almost all of the grid cells in
the sample contained at least some trees, there are major
variations in the density of trees per hectare in paddy fields
among the sample grid cells with a range from 0.8 to
44.6 trees/ha (Table 3). The bottom quartile (25 %) has
6.6 trees/ha, the median (50 %) is 11.6 trees/ha, and the top
quartile (75 %) has 16.7 trees/ha. The density of trees found
in this survey is considerably lower than was reported in
earlier surveys (Watcharakitti 1979; Watanabe et al. 1990;
Prachaiyo 1993, 2000). Although this difference may be
partly accounted for by use of different methods in our
survey and earlier studies (e.g., the total number of trees in
our survey may be somewhat undercounted because clumps
or clusters that may include several trees were counted as
single trees), the differences are so great as to suggest that
there has been a real decline in tree densities over time. The
fact that a recent survey in two villages in nearby central
Laos found densities similar to ours, with an average just
under 20 trees/ha in a newly established village with an
abundance of adjacent forest and 15 trees/ha in an old village without any adjacent forest (Kosaka et al. 2006) offers
support for this conclusion