An interregional trading model for roundwood products was
developed that recognizes the importance of demand centers (centers of forest
products manufacturing activity) and inventory in forecasting future harvests
and trade flows. A gravity model was constructed that considers the relative
position of each region vis-a-vis all others as a producer of stumpage and as a
consumer of roundwood products. The gravity model was incorporated in a
multi-region version of DPSupply (Teeter 1994, Zhou and Teeter 1996, Zhou 1998)
referred to as the Interregional DPSupply System
(IDPS).
Projections for growth, harvest, and trade in forest products were made for the
13 states of the southern region through 2025. Aggregate trends in inventory are
similar to those reported in the Southern Forest Resource Assessment (Wear and
Greis 2002). Inventory trends by product (pulpwood, sawtimber) and type
(hardwood, softwood) differ by state and are used to illustrate the advantages
of explicitly recognizing interregional trade in the projection system.
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The South is the major timber production region in the
United States. In 1997, nearly 58 percent of U.S. industrial roundwood and
three-fourths of total U.S. pulpwood was produced in the region (Smith et al.
2001). A number of projections made in the 1970s and 1980s (Haynes and Adams
1985), as well as the 2000 USDA Forest Service RPA Assessment (Haynes 2003)
predicted an increasing share for the U.S. South both in timber growth and in
removals.
This paper describes an interregional timber inventory
projection model that recognizes the importance of demand centers (centers of
forest products manufacturing activity), inventory dynamics, and trade flows in
forecasting future harvests. The model adapted work by Teeter et al. (1989) who
modeled interindustry trade and highlighted the interdependence of producing
regions. Drawing from that work, a gravity model was constructed that considers
the relative position of each region vis-a-vis all others as a producer of
stumpage and as a consumer of roundwood products. As a result, the model allows
for changes in the harvest levels among regions to accommodate imbalances in
inventory, changes in production capacity, and transportation costs from the
source of the raw material to manufacturing facilities.
An Interregional DPSupply Model
The Interregional DPSupply (IDPS) model utilizes a
combination of normative and positive approaches (Wear and Parks 1994) to
modeling timber supply. It models growth and optimal management decisions on the
level of individual representative stands (FIA sample plots). The optimality
criterion for management decisions is maximization of land expectation value
(LEV). By aggregating representative stands available for harvesting to the
subregional level, supply is modeled for four roundwood products: softwood
pulpwood, softwood sawtimber, hardwood pulpwood, and hardwood sawtimber. IDPS
allocates demands for individual products in the demand subregions among the
supply subregions using a gravity coefficient method.
