foot volume of saw timber in the State is -£1.7 
percent; a corresponding error for the total volume 
in cords was not computed, but it should be smaller. 
Growth Estimates 
Net growth was computed only on live saw-timber 
and pole-timber trees. Cull trees and hardwood limbs 
were not included in growth calculations. 
Measurements for growth calculations were 
obtained from increment borings taken from me- 
chanically selected trees on the sample plots measured 
for volume estimates. A total of 5,242 sample trees 
3.0 inches and larger in diameter were bored. In 
general, computational procedures consisted of add- 
ing the volume of small trees that grew to mer- 
chantable size or grew into a higher diameter-class 
group during the preceding 10-year period to the 
growth of the trees that remained in a particular 
diameter class. 
Sample tree diameters were increased by using 
the measured diameter growth of trees of the same 
diameter class. For instance, the average diameter 
growth of 8-inch trees was based on the growth of 
trees that were 8 inches in diameter at the start of 
‘the growth period, not on the last 10 years’ growth 
of an 8-inch tree. Also, an allowance was made for 
bark growth during this period. The projected vol- 
ume of the sample tree was then expressed as an 
annual percentage increase through the use of com- 
pound interest tables, and these percentages were 
applied directly to the growing-stock 
Mortality was obtained by special studies on the 
ground plots, and the total annual loss was deducted 
from total growth. 
volume. 
_ Growth of turpentined trees was determined by a 
special field study involving ring counts and radial 
growth measurements on stump and_ stem cross- 
sections of worked-out trees cut on logging and pulp- 
wood operations. 
Drain Estimates 
Following the completion of the forest inventory 
of Florida in 1949, the Southeastern Forest Experi- 
ment Station and the Florida Forest Service co- 
operated in a field survey to determine the volume 
of raw forest products used in Florida or shipped 
to out-of-State users in 1948. A complete canvass 
of sawmills and primary nonlumber plants in Florida 
and adjoining areas was made to obtain 1948 pro- 
duction of logs, bolts, and stumps. Contacts with 
The Timber Supply Situation in Florida 
treating plants, railroads, large utilities, and exporters 
were made for data on hewn cross ties, poles, and 
piling. 
The 1948 production of fuel wood, fence posts, 
and farm timbers was estimated through an area 
sample. Small areas totaling approximately one per- 
cent of the area of the State were selected mechan- 
ically from the Master Sample of Agriculture, a 
sampling system used by the Bureau of Agricultural 
Economics in agricultural sampling work. A complete 
canvass of each area was made to determine the 
amount of the items produced during 1948. The data 
were then expanded to give county and State totals 
(4). 
Additional information was needed to convert the 
1948 production data to commodity drain. To obtain 
this, a separate study was made on a random selection 
of the woods operations for each of the 10 leading 
products. The study was made on active operations 
in order to determine: (1) the extent of over- 
utilization or waste, compared to Forest Survey 
standards, in trees cut for the various products; (2) 
the species, tree sizes, log diameters, and quality 
of material used; (3) the species, size, and quality 
of trees ruined in cutting and logging operations; 
and (4) other information, such as bark thicknesses 
and length of bolts, for use in converting the in- 
formation to the different units of measure. 
Reliability of the Data.—Four general sources 
of error could affect the accuracy of the data used 
in the production and commodity drain estimates. 
These are reporting errors, canvassing errors, errors 
in compiling data, and sampling errors. 
Most producers of fuel wood, fence posts, and 
farm timbers, as well as some small sawmills and 
other manufacturers, furnished estimates of produc- 
tion rather than actual bookkeeping records. In- 
dividual errors caused by this are not likely to be 
large and may tend to be compensating; but it is not 
possible to measure them. Enumerating work was 
done by men familiar with the locality who had 
been especially trained to do accurate canvassing 
work. All records and computations were carefully 
checked to eliminate possible error. 
Sampling errors (standard errors of estimates) are 
the only errors that can be evaluated. They are 
measures of the reliability of the estimates based 
on the size of the sample and individual variations 
within it. 
53 
