One of the primary objectives of this study is to project 
prospective changes in the South’s timber resource. Projec- 
tions of changes in timber supplies, removals, growth, and 
inventories, along with projections of timber demands, pro- 
vide a means of identifying future or developing timber 
problems. These projections also guide many decisions on 
long-range commitments such as investments in plant and 
facilities, and timber management practices whose effects are 
realized over an extended period of time. Finally, projec- 
tions also provide the data base needed for analyzing the 
economic, social, and environmental implications of a 
range of policy and program options. The options currently 
being considered and appropriate to the South are analyzed 
in the following chapter. 
The projections reflect the quantified results of assumptions 
on the major determinants of changes in the timber re- 
source. There is no intent to predict that these projected 
trends in the timber resource will actually occur, nor that 
they should. In fact, it is expected that because of economic, 
social, and environmental implications associated with these 
trends, actions will be taken to change them in ways consid- 
ered more desirable. 
84 
Timber Resource Projection Methods 
The dynamic southern forests present complex problems in 
preparing resource projections. To deal with this effectively, 
a large data base and intricate and detailed analytical sys- 
tems to simulate resource changes have been developed. 
Projection Models 
Three distinct but closely related analytical systems were 
utilized. An updated version of the Timber Assessment Mar- 
ket Model (TAMM) was used to simulate roundwood har- 
vest (Adams and Haynes 1980). The Timber Resource 
Inventory Model (TRIM) was used to simulate changes in 
timber inventory, growth, and removals (Tedder and oth- 
ers 1987). Changes in timberland area and ownership were 
simulated with the Southern Area Model (SAM) (Alig 
1985). 
The Timber Assessment Market Model is a market equilib- 
rium system that projects long-range estimates of price, 
consumption, and production of timber products and stump- 
age for various regions in the United States. The system 
uses variables such as stumpage prices and growing stock 
inventory to develop roundwood supply equations for soft- 
woods and hardwoods. Timber removals for each owner- 
ship group are calculated by equilibrium modeling of 
timber supply and demand by the Timber Assessment 
Market Model. The Timber Resource Inventory Model uses 
timber removal calculations in projecting inventory 
volumes and growth. This information is fed back to the 
Timber Assessment Market Model, which then recalculates 
the equilibrium level of timber removals. This process is 
repeated iteratively until a tolerable convergence is attained. 
The Timber Assessment Market Model was extensively 
revised for use in this study. Major changes included 
reestimated equations based on data through 1985 for most 
relationships, a 15 percent tariff on Canadian exports to the 
United States, revised capacity series, and a switch from 
nominal to real Canada/U.S. exchange rates. The demand 
model was revised for changes in various end-use factors 
and for changes in panel product classifications into struc- 
tural and nonstructural groupings. It was calibrated by 
comparing its projections for 1977—84 with the actual data. 
In general, the demand projections used in this report start 
in 1990. 
The Timber Resource Inventory Model replaces the Timber 
Resource Analysis System (TRAS) used in previous For- 
est Service assessments of this type (Larson and Goforth 
1974). The Timber Resource Analysis System is a stand- 
table projection model in which the timber resource is aggre- 
gated by ownership, by softwood and hardwood, and by 
