Abstract:
This experiment was designed to investigate the use of volume
estimations from aerial photography and probability proportional to
size (PPS) sample selection in the development of a practical sampling
design for timber volume estimation on small land areas of
Pacific Northwest Douglas -fir (Pseudotsuga menziesii, Franco).
The major problem of measuring exact stand height to predict stand
volume from aerial photos was overcome by the development of two
new volume equations which use percent crown closure, visible
crown diameter and height classes as the independent variables. By
the use of height classes, the photo interpreter is required to separate
stand heights as to tall, medium or short. Equations are
presented for both board- and cubic-foot volumes. Two computer programs were developed which reduce office
calculations to a minimum. The programs compute photo volumes
per plot, total gross and net volume estimations per area, standard
errors and select the field plots to be sampled.
The sampling design was tested on four test areas, using both
quarter- and one-acre photo plots, and quarter-acre fixed-area and
variable-area field plots at four photo scales. Based on these results
a sample of about 20 field measured quarter-acre field plots combined
with a 100 percent photo cruise on 1:7,000 aerial photos would
be expected to produce gross volume estimations for a forty-acre
tract of + 10 percent. at a 68 percent confidence level.
