SOME FACTORS AFFECTING REPRODUCTION AFTER 
LOGGING IN NORTHERN IDAHO 1 
By J. A. Larsen 
Forest Examiner , Priest River Forest Experiment Station , Forest Service , United 
States Department of Agriculture 
In the virgin forest of northern Idaho, natural reproduction of desirable forest 
tree species after cutting is often very scant and disappointing. Not only do 
the defective and prolific weed species of western hemlock and grand fir prevent 
good establishment of western white pine, but also good reproduction and 
establishment of the pine on exposed slopes and flats is in most cases very difficult 
to obtain. The latter difficulty comes about either through failure of the seed 
to germinate or because the seedlings, many of which may spring from seed 
already in the forest floor at the time of cutting, do not withstand the hot, dry 
summer weather and the drying out of the soil. 
In order to throw light on this question of germination and survival, certain 
investigations, recorded in this paper, were made by the Priest River Forest 
Experiment Station in northern Idaho. These have to do with the effect of 
large clearings as compared with shelterwood and the uncut forest, germination 
of seed and establishment of seedlings on the various surfaces found after logging, 
and the influence of different aspects. 
INFLUENCE OF LARGE CLEARINGS 
In the first place, the mere opening of the forest by cutting affects the physical 
conditions of the site in a very marked degree, both by increasing air and soil 
temperature, evaporation, and rate of transpiration, and by causing extremes 
or dangerous fluctuations which prove injurious to seedlings. In order to gain 
information on this point, studies were conducted during the dry and warm 
summer of 1919 on sites offering comparisons of three different conditions: (1) 
250 feet within an old and uncut virgin forest of western white pine ( Pinus 
monticola) , western red cedar ( Thuja plicata ), western larch {Larix ocddentalis) , and 
grand fir ( Abies grandis) ; (2) at a point 400 feet east of the first site under about 
one-third overhead cover provided by leaving defective hemlock ( Tsuga hetero - 
phylla) and other species; and (3) on a wide and complete clearing to the south 
of the other two sites where all of the overhead trees were removed and the site 
fully exposed to sun and wind. These three locations were all found on a broad 
river bench at an elevation of 2,300 feet in the Priest River valley. 
Each station was equipped with maximum and minimum air thermometers of 
the United States Weather Bureau pattern, and air thermographs were placed 
in the stations in the open and in the uncut forest. These instruments were 
placed 4 \ feet above the ground within suitable shelter boxes. At each station 
there was one psychrometer and one Livingston cylindrical porous-cup atmometer. 
The latter was placed 6 inches above the ground, the bottle containing the 
water being entirely below the surface. 
Daily soil temperature readings and semiweekly soil-moisture samples were 
obtained at a depth of 6 inches near each station on a bare plot of ground 1 
i Received for publication June 19,1924—issued Nov., 1924. 
Journal of Agricultural Research, 
Washington, D. C. 
( 1149 ) 
Vol. XXVIII, No. 11 
June 14,1924 
Key No F-17 
