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Major Phases of Survey 
HE major phases of the Douglas-fir survey 
were four—the inventory phase, the study of 
forest depletion, estimates of forest growth, 
and a determination of present and future timber 
requirements. An analysis of this information for 
the purpose of developing principles and policies to 
make the forests contribute most in services region- 
ally and nationally leads inevitably into a consider- 
ation of land use planning, future supplies of timber 
in relation to industrial development and require- 
ments, and forest management. Although the 
requirements phase is discussed here only for the 
region, the subject is much broader than this; it is 
planned to integrate it with similar information 
from other regions for publication later as a report 
on forest-products requirements for the whole 
country. 
The inventory phase of the forest survey was 
undertaken first in the spring of 1930. Its principal 
purposes were to obtain: 
1. Volume of the present timber stands, by species and 
by ownership class. 
2. Areas of the several types, by ownership class. 
3. Areas of the immature-conifer types by age class and 
degree of stocking. 
4. Maps showing location of each of the forest types. 
5. A classification of timber stands according to economic 
availability for logging. 
6. A classification of forest area according to site quality. 
The existence of considerable information, par- 
ticularly on the merchantable timber areas which 
comprise about half of the 29 million acres in the 
Douglas-fir region, made it practicable to rely on 
checking and compiling the information already 
available from public or private cruises, maps, and 
reports. ‘This was supplemented with field exami- 
nations of all remaining areas. 
SSS 
_ The work of the inventory phase was conducted 
in four steps: (1) Collection of all existing informa- 
tion, (2) checking and adjusting to a common 
standard all usable existing timber estimates, (3) 
field examination of areas not covered by usable 
information, (4) compilation of data collected.” 
The immediate object of the depletion phase of 
the forest survey was to determine the quantity and 
kind of timber annually removed by cutting or 
killed by fire, wind throw, insects, disease, and all 
other causes; in short, the extent and character of 
the drain on the forest capital. The ultimate object 
was to obtain data needed for an analysis that would 
determine the trends of depletion and growth, 
present and potential, and the net result of the two 
trends. 
Depletion as considered in this study does not 
include ordinary endemic losses due to such causes 
as diseases, surface fires, wind throw, and insects. 
Such normal losses have been allowed for in the 
construction of the yield tables used in calculating 
growth. Depletion as here considered involves 
only timber killed or removed by logging, by fires 
that kill entire stands, by windstorms of major 
intensity, and by insect epidemics. 
To estimate the rate and quantity of current and 
potential growth in the forests of this region would 
be simple if rates of growth were constant for all 
conditions. Instead, they vary among individual 
trees according to species, age, and dominance; 
among individual forest stands according to type, 
site, average age, and stocking; and among aggre- 
gates of stands according to the growth character- 
2 The organization of the field work and the detailed 
procedure involved in each of these four steps are described 
in the Appendix, p. 146. 
