Some of the projected increase in plantation pine area is from 
the planting of pine after mixed pine—hardwood stands are 
harvested. The area in mixed pine—hardwood is projected to 
drop by 6 million acres, or 22 percent, over the projection 
period. Much of this reduction occurs on forest industry 
lands. 
The total hardwood area in the South is projected to de- 
crease by approximately 12 million acres, or 13 percent, by 
2030. Much of this reduction is in the upland hardwood 
type, which currently occupies over one-third of the south- 
ern timberland base. 
The projected drop in upland hardwood area results from 
several factors. First, some of the upland hardwood area is 
expected to be converted to planted pine, especially on in- 
dustry lands. Second, some of the timberland on farms that 
is converted to cropland is currently in upland hardwoods. 
The last major reason is conversion of upland hardwood 
acreage to other land uses such as urban and built-up uses. 
Bottomland hardwood area is also projected to decrease, by 
4 million acres. However, the rate of clearing of bottomland 
hardwood forest for cropland is expected to slow down. 
Some bottomland hardwood area is projected to be with- 
drawn from the timberland base in States such as Louisi- 
ana for management by State agencies to protect wildlife 
habitat and other nonmarket resources. 
The projected changes by State are in general consistent 
with the Southwide changes. 
Projected Changes by Site Class—Site, a measure of the 
inherent capacity of land to grow trees, is one of the im- 
portant determinants of changes in the timber resource. 
However, analysis of data first assembled around the mid- 
1960's indicates there have been no major net changes in the 
regional distribution of timberland by site class. The last 
two surveys in the Southeast indicate that overall there have 
been only relatively minor shifts in the site-class distribu- 
tions toward the higher classes. 
Net changes in the distribution of site classes by forest type 
have also been relatively small except for the bottomland 
hardwood class. A large drop in the bottomland hardwood 
area in the upper site-class was due largely to the conver- 
sion of such high-quality timberland to cropland, including 
many acres of soybeans in bottomlands. 
Based on the analysis of historical site data, it was assumed 
in this study that the distribution of timberland among the 
site classes would not change significantly over the projec- 
128 
tion period. However, the conversion of many forest acres 
to pine plantations implies a shift toward higher site land. 
This reflects the upgrading of substantial acreages of low- 
productivity land in the Coastal Plain that are being drained, 
site prepared, bedded, and planted to pine. 
Assumptions on Timber Yields 
The above projections of area change provide part of the 
data needed for projecting changes in net annual timber 
growth and inventories. 
Since volume and growth estimates are derived from acre- 
age movements through assumed yield tables, assumptions 
on timber yields are also crucial in using the Timber Re- 
source Inventory Model to project timber resource changes. 
Empirical yields developed for major forest types in the 
Southeast from forest survey data provided measures of the 
proven performance of fully stocked stands in the region 
(McClure and Knight 1984). Assumptions on yields were 
derived from data collected on some 24,775 forest survey 
plots established randomly throughout the Southeast. These 
data were screened to identify those plots in fully stocked 
stands based on forest survey standards. The plots in fully 
stocked stands were further divided into three broad site 
classes within each of the five broad management types. 
Average volumes per acre were calculated for the fully 
stocked stands by 5-year age classes. 
Compilation of the average volumes per acre by 5-year age 
classes was possible in the Southeast because forest survey 
crews there record the actual age of each timber stand 
sampled. Even-aged stands are assumed, and no mixed-aged 
classifications are permitted. In the compilations, the age 
class represents the midpoint of the class. For example, the 
15-year age class includes stands 13 to 17 years old. 
In the South Central region, forest survey crews record 
10-year age classes and recognize mixed-aged stands. The 
empirical yields developed by 5-year age classes in the 
Southeast were used to help refine the broader age classes 
in the South Central region and enabled the development 
of consistent basic resource units for the Timber Resource 
Inventory Model input for the entire region. Forest survey 
data in the South Central region generally supported the 
empirical yields developed in the Southeast, with the 
exception of yields in the upland hardwood management 
type. Yields for this type were reduced by 15 percent for 
the South Central region. 
These empirical yields were subjected to widespread tech- 
nical review by representatives of the States, forest 
