SAMPLING VEGETATION ATTRIBUTES - New Mexico NRCS - US ...

10
STUDY DESIGN AND ANALYSIS
Macroplot size also depends on the size and shape of the quadrats that will be
used to sample it. The sides of the macroplot should be of dimensions that are
multiples of the sides of the quadrats.
(1) Macroplot layout Pick one corner of the macroplot to serve as the beginning
for sampling purposes. Drive an angle iron location stake into the ground
at this corner. Determine the bearing of the macroplot side that will serve
as the x-axis, run a tape in that direction and put an angle iron stake at the
selected distance. This serves as another corner of the macroplot. Leave
the x-axis tape in place for sampling purposes. Return to the origin and
determine the bearing of the y-axis, which will be perpendicular to the xaxis.
Run a second tape along the y-axis and put an angle iron stake in the
ground at the selected distance. This serves as the third corner of the
macroplot. If desired, a fourth stake may be placed at the remaining
corner, but this is not necessary for sampling since sampling will be done
using the two tapes serving as the x- and y-axes. See Figure 2 for an example.
Leave the tapes in place until the first year’s sampling is completed.
50 m
angle iron
0 m
0 m 100 m
Figure 2. The two sides of a 50 m x 100 m macroplot, delineated by two tape measures. Both tapes begin
with their 0 point at the beginning. Note placement of angle irons at three of the corners.
Be sure to document the directions of the x- and y-axes so that the
macroplot can be reconstructed if one of the angle iron stakes is missing.
(2) Quadrat locations Quadrats are located in the macroplot using a coordinate
system to identify the lower left-hand corner of each quadrat.
(a) For example it has been determined from the pilot study that 40
samples are needed using a 1 m by 16 m quadrat. The quadrats are to
be positioned so that the long side is parallel to the x-axis. On a 40 m
x 80 m study site (see Figure 3), the x-axis would be the 80 m side.
The total number of quadrats (N) that could be placed in that 40 m x
80 m rectangle without overlap comprises the sampled population. In
this case, N is equal to 200 quadrats.
(b) Along the x-axis there are 5 possible starting points (which always occur
at the lower left-hand corner of each quadrat) for each 1 m x 16 m
quadrat (at points 0 m, 16 m, 32 m, 48 m, and 64 m). Number these
points 0 to 4 (in whole numbers) accordingly. Along the y-axis there are
40 possible starting points for each quadrat (at points 0 m, 1 m, 2 m, 3 m,
4 m, and so on until point 39 m). Number these points 0 to 39 accordingly
(again in whole numbers)