industries, and universities. There were several meetings of 
technical review groups in which the assumptions on timber 
yields were discussed at length. Numerous revisions in the 
assumptions on timber yields were discussed in an attempt 
to reach a consensus among the technical experts. Much of 
the discussion centered around the assumptions on timber 
yields for pine plantations because of their importance in 
the region. Finally, fairly broad agreement was reached on 
the assumptions on timber yields with some acknowledged 
exceptions. Generally, the empirical yields developed from 
forest survey in the Southeast were used, with some minor 
‘revisions, for the natural stands and the pine plantations on 
farmer and other individual private lands. New, higher 
yields were developed and used for pine plantations on 
industry, other corporate, and public ownerships. It was 
assumed that more-intensive site preparation and manage- 
ment on these ownerships would result in higher yields. 
A 10-percent increase over the base yields was assumed for 
pine plantations established with genetically improved stock 
regardless of ownership. A 15-percent increase over the base 
yields was assumed for the highest management intensity 
on forest industry and corporate ownerships. For manage- 
ment intensities where thinning is practiced, no overall 
increase in cubic-foot yields was assumed. The volume 
removed during thinning was subtracted from the volume at 
final harvest. The same technical groups responsible for 
development of assumptions on timber yields guided the 
assumptions on enrollment rates into the higher manage- 
ment intensities, by ownership. 
The highest timber yields (growth) are 
achieved in pine plantations, particularly 
those planted with genetically improved 
stock and intensively managed. 
Assumptions on timber yields also involve the relationship 
between the initial timber inventories, as compiled into 
basic resource units, and the assumed timber yields. The 
assumed timber yields developed and adopted for this 
assessment of southern timber supplies were intended to 
reflect the prospective yields of fully stocked stands, based 
on forest survey stocking standards. The initial timber 
inventories comprise stands that span the full range of 
stocking conditions. In this study, the compilation of initial 
timber inventories into basic resource units recognized the 
following stocking levels, based on forest survey standards: 
(1) fully stocked (100 percent or more), (2) medium stocked 
(60—99 percent), and (3) poorly stocked (less than 60 per- 
cent). These stocking percents refer to growing stock trees 
only; the stocking of rough and rotten trees was ignored. 
Ideally, the average volumes per acre for fully stocked 
stands should coincide with the base timber yields assumed 
for that particular management type and site, but some 
differences were accepted. Reasons for the differences 
include (1) the wide range of stocking among the stands 
considered fully stocked; (2) stocking of older, residual 
trees in a given age class; (3) stocking of younger trees that 
have filled in holes within a given age class; and (4) varia- 
tions in the species mix within a management type. 
As part of the Timber Resource Inventory Model input, 
average stocking level midpoints were developed to quantify 
the relationship between the average volumes per acre in the 
initial inventories and the assumed timber yields. In the 
projection process, two fundamental options are available 
affecting the application of the assumed timber yields: 
(1) the yield table option, and (2) the approach-to-normality 
option. In the yield table option, volume per acre for a 
given age class is the product of the assumed yield for that 
age class times a constant stocking level midpoint for that 
management intensity and stocking level. In the approach-to- 
normality option, stocking level midpoints approach 1.0 
over time. An equation is used to quantify the rate of 
approach. 
In the early stages of this study, both options were tested. 
Based on the results of these tests, the approach-to- 
normality option was selected with full approach in the 
younger age classes and one-half the full approach in the 
older ages. Selection of this option assumes that the stocking 
in understocked stands will gradually improve over time 
Appendix tables 3.15—3.20 summarize the base timber 
yields used in the Timber Resource Inventory Model in the 
projections of prospective timber supplies in the South. 
These assumed yields are for the minimum management 
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