WESTERN YELLOW PINE IN OREGON. 
27 
Table 11.— Average merchantable volume in board feet of yellow-pine trees at various 
ages for 10 typical localities in Oregon. 
Age, 
years. 
20 
40 
60 
80 
100 
120 
140 
160 
180 
200 
220 
240 
260 
280 
300 
320 
340 
360 
380 
400 
420 
440 
460 
480 
500 
Whit- 
ney and 
Austin. 
Look- 
ing- 
glass 
Creek. 
Win- 
lock's 
Mill. 
Ochoco 
Creek. 
Sisters 
(1). 
Lapine 
(1). 
Fort 
Kla- 
math. 
Odessa. 
Mead- 
ow 
Lake. 
Em- 
body. 
Aver- 
age, i 
Volume of tree, in board feet. 

20 
50 
95 
160 
250 
360 
490 
630 
780 
920 
1,050 
1,170 
1,290 
1,400 
1,510 
1,610 
1,700 
1,790 
1,870 
2,010 
2, 150 
10 
115 
180 
250 
320 
400 
480 
570 
670 
770 
880 
990 
1,110 
1,230 
1,340 
1,440 
1,640 
1,820 
55 
92 
140 
172 
279 
407 
544 
688 
835 
982 
1,130 
1,279 
1,430 
1,431 
1,564 
1,702 
1.S38 
1,955 
2,017 
2,155 
2,322 
80 
230 
400 
600 
800 
1,000 
1, 190 
1,370 
1,550 
1,730 
1,910 
2,090 
2,260 
2,430 
2,600 
2,770 
2,940 
20 
90 
180 
300 
440 
580 
710 
830 
950 
1,060 
1,170 
1,280 
1,380 
1,480 
1,580 
1,680 
1,770 
50 
150 
205 
275 
350 
430 
510 
590 
670 
750 
835 
925 
1,020 
1,110 
1,210 
1,300 
1,390 
1,480 
1,570 
1,660 
1,750 
150 
260 
380 
500 
605 
705 
810 
935 
1,070 
1,230 
1,430 
20 
105 
195 
290 
390 
500 
610 
730 
860 
980 
1. 110 
1,240 
1,370 
1,500 
1,600 
1,790 
1,930 
2,210 
2,490 
80 
210 
370 
540 
730 
920 
1,110 
1,300 
. 1,480 
1,660 
1,820 
1,980 
2,120 
2,260 
2,400 
2,680 
2,960 
20 
75 
140 
205 
280 
365 
470 
590 
740 
900 
1,090 
1,270 
70 
165 
265 
375 
480 
600 
720 
840 
960 
1,070 
1,170 
1,260 
1,320 
1,370 
1,420 
1,450 
1,490 
1,510 
1 The average of 20 separate stands in Oregon, the data for only 10 of which are given in the above table. 
FACTORS AFFECTING GROWTH. 
The most important single factor that affects growth is the amount 
of available soil moisture. Provided that climate and drainage are 
satisfactory, the most rapid growth is found in well-watered situa- 
tions — in coves, on moist north and south slopes, and on benches. 
Heat also tends to promote the vigor of growth, provided soil and 
moisture conditions are satisfactory; hence at the higher, colder ele- 
vations and in cold situations growth is slower. 
Another factor which materially affects the rate of growth of indi- 
vidual trees is the density of the stand. In the study of the crown 
space needed by trees of various sizes (see Table 6) it was found that 
trees make their maximum growth when they have more space than 
they do in the average virgin forest, open as it is. Beyond a certain 
point increase in available crown space apparently does not cause an 
increase in the growth rate. In some situations an excess of room 
seems to inhibit growth, perhaps because it subjects the tree to 
excessive exposure to wind and evaporation. It is natural, to expect 
that selection cuttings such as are practiced on the National Forests 
(described in the chapter on " Management ") will stimulate the 
reserved trees to more rapid growth, and such is found to be the case. 
In a detailed study 1 of several areas in the Blue Mountains, partially 
logged over several years ago, the increase in the basal area growth of 
1 Manuscript report by R. H. Weitknecht, assistant forest ranger. 
