44 BULLETIN 1200, U. S. DEPARTMENT OF AGRICULTURE. 
the absence of fires and the accompanying increase of soil moisture 
are emphasized in area 4. The effect of two years of freedom from 
fires is shown in the increased humus and moisture in area 5. 
Sprouting from the roots causes a brush cover to form quickly after 
each fire in this region. Better moisture conditions are thus estab- 
lished by the brush cover, and invasion by forest-tree species is 
made possible. 
The first generai fires in this region occurred in 1854, soon after 
the mining rush of 1851. Since that time frequent fires have oc- 
curred, and some of the areas have been reburned a number of times. 
‘The most barren slopes, however, still have traces of a former forest. 
The young Douglas fir is gradually establishing itself under the 
protection of the brush and oak trees. Ninety-five per cent of the 
seedlings occur under single bushes or in areas of shrubby growth. 
The age classes represented in these brush areas indicate that the 
seed is being produced by the adjacent seed trees. The fact that 
practically no reproduction occures on the slopes beyond the in- 
fluence of seed trees shows that all sources of seed within the area 
have been conpletely eliminated by repeated fires. The establish- 
ment of the seedlings in different positions in relation to seed trees 
is brought out in Table 20. ~ 
TABLE 20.—The occurrence of Douglas-fir seedlings in relation to seed trees. 
Number 
of seed- Age 
Distance from seed trees. lings per | classes, 
square | years. 
rod. | 
| 
13 chains ! above seed trees on southwest slope. -........ 22-2 eee eee e cece ence eee ees 20 | 4 to 22 
Leham above seed trees ‘on: southwest slopes a. 224 ice. oo ass ae 16}; 2to018 
Mehanrbelow Seed trees.on souibwest SlOpes:..-. 2353406. om aoe fone ee een ~ SB) eto 8? 
3 chains below. seed trees on Southwest slope... ... 0. .2...cnccccecc enc ecceccccesece--:- | Pay) 6 to 15 
{ 
11 chain equals 66 feet. 
GROWTH.** 
RATE OF GROWTH IN YOUNG STANDS AND EFFECT OF DENSITY 
ON GROWTH. 
The density of the stand of young growth not only affects its de- 
velopment during its early life, but it has an influence throughout 
the life of the trees and even upon their usefulness when cut. 
Rate of growth is often the factor which determines the success of 
a species. The Douglas-fir seedling produces a more rapid Height 
growth during its early life than does any of its associated species. 
The average height growth during the first few years may be small, 
as a result of early or late frosts which often cause a bushy form of 
seedling. When once the leader is formed, however, the height 
growth is very rapid. 
The effect of the density of the stand on the height and diameter 
erowth in young stands of Douglas fir is shown in Table 21. 
14 Growth figures are based on data gathered by E. J. Hanzlik, T. T. Munger, and the 
staff of the Wind River Forest Experiment Station. 
