FiO; R EO Saf (ROE SO UR GeESS: (O70 bh Eee DeOeUNGyErARS F- she li RR Es Gale @meN 
Forest Growth 
>> 
HEN conclusions had been reached regard- 
ing the extent of the forest capital of the 
Douglas-fir region and the rate at which it 
is being depleted, the next step in the survey was to 
calculate the rates at which this forest capital is 
being and might be replenished by growth. 
In general, the forest stands of the region may be 
divided into two categories—those in which there is 
net volume growth and those in which growth is off- 
set by mortality and decay. It was assumed in the 
survey that net increment in stands between the ages 
of 160 and 300 years is balanced by net loss in older 
stands, and estimates of growth were therefore re- 
stricted to stands not more than 160 years of age (2). 
Because most of the growing stands are even- 
aged, growth in all stands was calculated on the 
basis of growth in even-aged stands and average 
ages were assigned to the small areas of uneven-aged 
stands. 
Briefly, growth was calculated by applying rates 
to areal statistics of type, age, stocking, and site 
obtained in the inventory phase of the survey. 
Classification of forest lands and stands by these 
variables is described in pages 14 to 38. 
Table 21 shows what percent of the 11 million 
acres of growing stands in the region is occupied by 
each of five type groups. The conifer stands total 
10 W. H. Meyer devised the methods used in computing 
growth values and directed the computational work. P. A. 
Briegleb is the author of the text of this section. 
publications presenting results of the growth phase of the 
forest survey are (1) the station’s Forest Research Notes 
No. 17, Pulpwood Resources of Western Oregon and West- 
ern Washington, which includes some growth data for stands 
of pulpwood types, and (2) its Forest Research Notes No. 20, 
Forest Growth in the Douglas-Fir Region, which gives de- 
tailed growth statistics by broad ownership class for each 
unit and county of the region and briefly discusses the growth 
Previous 
study and its results. 
54 
Ke 
TABLE 21.—Composition of growing stands, in terms of total area 
occupied 
Type group Conifer All types 
J mnes All types 
Percent | Percent 
Douglas-firses nen eee eee aa ee es 85. 2 | 76.5 
Spruce:hemlocksss-- seater as ee eee 9.2 8.3 
Ponderosa: pineemensan see tae ome eee enen mee 1.9 GY 
Other! coniferssae ssa er oe na oa eee 3.7 3.4 
Lotaliconifers savrsamesea ees eear ee ane oer 100.0 89.9 
TEL ar W.00G Beran eae ae ee eee tes ee ae ee ee 10.1 
Granditotalieee creamer ann seesin Paes | Mee a eee 100.0 
nearly 9 acres to 1 of hardwoods, and approxi- 
mately 85 percent of them, by area, are of types in 
which Douglas-fir predominates. 
Growth rates derived from standard Douglas-fir 
yield tables (72) were applied to all growing conifer 
stands, in the belief that application of these rates 
to stands of types other than Douglas-fir would lead 
to adequate, conservative estimates. Findings of 
the recently completed study of spruce-hemlock 
yield in the region (73) indicate that spruce-hem- 
lock forests (fig. 16) usually produce materially 
greater volumes than would be estimated by use 
of the Douglas-fir yield tables. Because of the rela- 
tively small extent of growing spruce and hemlock 
stands, however, the procedure employed resulted 
in no serious underestimate of forest growth in the 
region as a whole. Analysis of results of the 
recently completed study of ponderosa pine yield 
(74) indicates that application of the Douglas-fir 
growth rates as modified for survey use to ponderosa 
pine stands has resulted in estimates satisfactory for 
the present purpose. 
For application to actual stands the yield-table 
growth rates were reduced by the ratios of actual 
