intensity (level 1). In these tables, high sites include those 
acres capable of growing 85 or more cubic feet of wood per 
acre per year, based on fully stocked, natural stands. 
Medium sites are capable of growing 50 to 84 cubic feet per 
year; poor sites, 20 to 49 cubic feet. 
Other Assumptions 
Other key assumptions affecting the projection results 
include (1) enrollment rates into the higher management 
intensities, (2) minimum harvest ages and the allocation of 
harvest among age classes, and (3) the amount and timing 
of thinnings. Although recent Forest Survey findings 
provided some useful information in the development of 
these assumptions, they were primarily based upon the 
consensus of technical review groups composed of members 
from State forestry agencies, forest industries, forestry 
schools, and other consultants. As one would expect, expert 
opinions on these assumptions varied considerably, and 
limitations within the projection models restricted the range 
of options. For example, the Timber Resource Inventory 
Model will accommodate a maximum of five management 
intensities. 
Enrollment Rates—For pine plantations, up to five levels 
of management intensity were recognized: (1) regular 
planting stock without thinning, (2) regular planting stock 
with thinning, (3) genetically improved planting stock 
without thinning, (4) genetically improved planting stock 
with thinning, and (5) genetically improved planting stock 
without thinning but with the most intensive site-preparation 
and management practices. 
Although the proportions varied by ownership, approxi- 
mately 15 percent of the pine plantations already established 
as of the dates of the base data were assumed to have been 
established with genetically improved planting stock and 
were entered in management intensities 3 and 4. Initially, 
no acres were placed in management intensity 5. Rates of 
commercial thinning determined from the most recent forest 
surveys were used to estimate the number of acres in man- 
agement intensities 2 and 4. 
In the first 5-year projection period, 1980-85, 70 to 75 
percent of all new pine plantations were assumed to be 
planted with genetically improved stock. These percents 
were increased until 1995, at which time it was assumed 
all new pine plantations would be established with gen- 
etically improved stock. In the first projection period, 20 
percent of the new pine plantations established on forest 
industry land were enrolled in management intensity 5. This 
percent was increased each period until 1995. Beyond 
130 
1995, 50 percent of all new pine plantations established on 
industry land were enrolled in management intensity 5. 
Slightly lower levels of management intensity were assumed 
on the other corporate land. On the farmer and other 
individual private ownerships, only 5 percent of the planta- 
tion acreage was enrolled in management intensity 5. 
Except for natural pine stands on medium and high sites, 
only one level of management intensity was assumed for 
natural stands. For natural pine stands on medium and high 
sites, a second management intensity with thinning was 
assumed. Rates of commercial thinning, by ownership class, 
were developed from the most recent forest survey data 
available. 
Allocation of Harvest—The Timber Resource Inventory 
Model offers the user several controls over the allocation 
of harvest. One of these controls is the specification of a 
minimum harvest age for each grouped resource unit (owner- 
type-site combination). Volume on acres supporting timber 
stands younger than this minimum harvest age cannot 
contribute to meeting the timber demands through final 
harvest. Another control is the selection between two 
harvest options: (1) harvest oldest stands first, or (2) specify 
the percent of the harvest to come out of each eligible 
age class. In the latter option, if a particular age class is 
exhausted before the demand is satisfied, the remainder of 
the harvest from that resource unit is removed on the oldest- 
first basis. 
Thinning is a widely used management 
practice. It is designed to increase the value 
of the timber at final harvest and does not 
significantly change yields in terms of 
volume of timber growth. 
