A dot grid, with 100 dots per primary sampling unit, was utilized to 
measure average crown closure of the dominant stand. The grid was randomly 
overlaid on each unit three times, and the mean count was assumed to index 
average crown closure. 
A plastic template with three randomly located dots was placed on each 
primary sampling unit to select trees for height measurement. The height 
of the nearest dominant tree to each dot was estimated twice, using a pocket 
stereoscope and parallax bar (Avery, 1966). Average height of trees in 
the dominant stand was assumed to be the mean of the two height measurements 
for each of the three trees measured. 
Analysis of 1:120000 Imagery 
The primary sampling units selected for measurement on the 1:15840 
imagery were also identified on the 1:120000 imagery. Although care 
was exercised in this transfer, possible errors may have resulted from 
differences in scale, position of units on imagery, and parallax between 
the two types of imagery. 
A dot grid, with approximately 36 dots per primary sampling unit, was 
employed to assess forest density conditions on the 1:120000 imagery. This 
grid was a 35 mm slide that was produced by photographically reducing a 
larger dot grid. Several colors (black, blue, brown, and orange) of 
dots were initially evaluated, but it was decided that black dots were 
best in terms of visibility. 
Crown closure was estimated at four levels of magnification (7X, 10X, 
15X, and 25X) using a variable power microscope. At each level of magnifi 
cation, the dot grid was randomly placed on a delineated primary sampling 
unit, a glass plate was placed over the dot grid and imagery to prevent 
damage, and dots landing on what appeared to be tree crowns were counted. 
The mean of three counts was assumed to index average crown closure. 
Development of Basal Area Estimates 
The development of ground estimates of basal area required the 
translation of high altitude (1:120000) forest density assessments (crown 
closure) to ground estimates of basal area, using 1:15840 imagery as an 
intermediate adjustment basis. To achieve this development, the following 
relationships were sequentially required: 
(1) BA = f (BA ) 
g P 
where BA^ 
estimated ground basal area 
estimated 1:15840 imagery basal area