June 21, 1924 
A Study of Douglas Fir Reproduction 
1235 
after apparently becoming established, to combat the natural conditions under 
which they must grow. 
It was found that only 32 per cent of the trees on the control plot in the 1923 
count were 3 years and older, while on the selection plot these reached 48 per cent. 
Upon the shelterwood plot 51 per cent were 3-year seedlings, and 64 per cent 
upon the clear-cut plot. 
The different species were represented in the 1923 surviving class by the 
following percentages: 
' 
Clear-cut 
Control 
Shelterwood 
1 : : 
Selection 
Douglas fir__ 
62 
57 
80.3 
85 
Engelmann spruce_ 
20 
36.5 
19.2 
12.7 
Limber pine. _ 
18 
6.5 
0.4 
2.1 
Yellow pine___ 
0 
0 
0.1 
0.2 
One object of the cutting experiment was to secure a young stand of Douglas 
fir to the exclusion of other species and, as will be seen, the shelterwood and 
selection plots have come closest to securing a fulfillment of this object. To a 
large extent, success in securing reproduction is dependent upon the seed supply, 
which has been abundant on all plots but the clear-cut. The high percentage 
of survival that this area shows indicates not so much growing conditions superior 
to the other areas as that little new reproduction is coming in. What does 
appear is mainly confined to the west (windward) and south sides of the plot, 
adjacent to heavy timber. It is evident that 1 acre is too large an area to be 
successfully reseeded from the sides when in the form of a square. 
In general, the humus on the clear-cut plot is too deep to favor new reproduc¬ 
tion, and an accumulation of new humus in the form of aspen leaves is beginning 
to cover the soil with a layer which seedling roots find it difficult to penetrate. 
The entire area is now covered with a heavy stand of aspen, some of which is 
15 feet in height. While this is not so thick as through shade and moisture 
competition to preclude the possibility of fir reproduction, it is gradually building 
up such a barrier upon the ground as to offer serious hindrance to any reproduction 
that might appear despite the lack of seed. 
The selection plot ranks low in percentage of spruce reproduction because it 
is the only treated plot having no spruce seed trees on its windward side. In 
general it has furnished as much fir reproduction as has the shelterwood plot, 
but it docs not stand as high in survival of this species. It is quite possible 
that this is due to more favorable location of the shelterwood plot, as will be 
shown; but natural conditions of growth also favor the shelterwood plan in 
stands like this that are mostly even-aged. 
MOISTURE A DETERMINING FACTOR 
The results of several years’ investigation of climatic factors upon the plots 
lead to the following interesting deduction regarding moisture supply: During 
the early part of the year moisture conditions are most favorable in the old- 
growth stand, where wind movement and insolation, the chief factors in evapora¬ 
tion, are at a minimum. The selection and then the shelterwood areas follow 
in order. Because of its exposure, the clear-cut plot shows the lowest percentage 
of soil moisture for the whole season. Since soil moisture appears to be a con¬ 
trolling factor in Douglas fir reproduction, any considerable amount of early 
germination on the clear-cut area is made difficult. However, there is less sea¬ 
sonal variation in moisture here and a more even supply than under any of the 
