Abstract:
This study was a test of eight basal area factors and five point
sampling cluster patterns in a computer oriented sampling study of
coastal Alaska old-growth spruce-hemlock stands. It was an attempt
to learn which basal area factor and which type of point sample cluster
pattern should be used in such stands. A. test of the effect of stand
density on point sampling was also made.
All trees 3. 0 inches d. b. h. and larger on ten 3. 5 acre areas
were measured and mapped in the field. Five of the areas had crown
densities of from 40 to 69%, and the other five had crown densities of
70% or more, as determined from aerial photographs.
The computer measured basal areas per acre for all forty of
the basal area factor/sample cluster combinations on each of the
stem mapped areas. These average basal areas were summarized
for the five sampled areas in each density and analyzed in two ways.
Analysis of variance was used to test for significant difference of
precision and accuracy among the eight basal area factors, among
the five sample cluster patterns, and between the two density classes.
A chi-square analysis was used to determine the relative accuracy of
the designs under test.
Results of the analysis of variance indicated that there were
highly significant differences among the variances of the basal area
factors tested and a significant difference among the variances of the
sample cluster patterns tested. There was no significant difference
between the variances of the two stand density classes tested. No
significant interaction was observed among the sample variances for
the sets of variables tested.
There were highly significant differences among the accuracies
obtained with each of the basal area factors and with each of the sample
cluster patterns tested. There was no significant difference between
accuracies of the density classes tested. A significant interaction
was observed between the accuracies of the basal area factors
tested and the accuracies of the cluster patterns tested.
The data of this study indicated that samples from full density
stands measured with large basal area factors tended to overestimate
the true basal area of the stand. This overestimate increased as
size of basal area factor increased. For that reason, and until further
study denies that this bias exists, maximum basal area factors of 30 and 40 are recommended for sampling in medium and full density
stands respectively. The data also indicate that, of the five
cluster patterns tested, a 15 point cluster pattern provided the most
accurate and most precise measure of basal area per acre.
