June 14, 1924 
Factors Affecting Reproduction after Logging 
1157 
very hot days the relative humidity of the air reaches the extremely low points 
of 10 to 20 per cent. From the many sowing tests installed in 1913 on the 
northeast slope, the southeast slope, and the flat with sandy soil, in the course 
of which 84 different samples of seed were used, germination of western white 
pine, cedar, hemlock, larch, and grand fir was proved to be as good on exposed 
sites as on the most favored aspects; but only western yellow pine and Douglas 
fir seedlings survived the peak of the hot weather on the southwest aspect. 2 
The greater death rate occurred when soil became very warm and dry. Often 
sites such as result from unrestricted clearings on south and west aspects, there¬ 
fore, become too dry and too hot for seedling survival of western white pine 
and other moisture-loving species. 
Table VI .—Extremes of surface soil temperature and moisture on different aspects 
in August 
(Records of 1913,1915, and 1916, northern Idaho) 
Location 
Surface temper¬ 
ature 
Surface soil 
moisture 
Soil moisture at 
6-12 inches depth 
Average 
Maxi¬ 
mum 
Average 
Mini¬ 
mum 
Average 
Mini¬ 
mum 
Northeast slope.. 
°F. 
60.2 
>76.9 
75.3 
75.9 
°F . 
85.0 
125.0 
115.0 
118.0 
Per cent 
43.6 
7.7 
7.0 
19.1 
Per cent 
10.7 
0.5 
2.1 
3.4 
Per cent 
42.9 
14.6 
13.4 
38.3 
Per cent 
11.9 
2.6 
5.0 
11.0 
Southwest slope -... 
Larch fir flat ®* .... 
White pine flat 3 * * & __ 
a Soil of sandy loam. b Clay loam soil. 
SUMMARY 
Large openings made in the forest cover by clear-cutting cause increase in 
air and soil temperature, evaporation and moisture deficit, which present un¬ 
favorable conditions for reestablishment of moisture-loving species. Further¬ 
more, changed surface conditions resulting from large openings and vegetation 
on areas completely cleared may defeat natural regeneration altogether. 
Surfaces of ash and bare mineral soil when loose offer the most favorable 
conditions for rapid germination and establishment of seedlings provided seed 
is immediately available, but where overhead or adjacent trees must supply the 
seed for natural restocking over a period of years, a loose and protected surface 
such as is provided by needle duff and light vegetation is more favorable. The 
tests show that Engelmann spruce and western larch, and in this class may be 
placed western red cedar and western hemlock, germinate well on duff surfaces, 
but have very poor survival on account of their short roots. The extremely 
high surface soil temperatures which occur on cleared and exposed flats and 
south slopes are injurious to establishment of seedlings of western white pine, 
cedar, and hemlock, and this explains the general scarcity of these species on 
sites exposed to sun and wind and the difficulty of restocking these after clear- 
cutting on a large scale. 
A method of cutting which would provide smaller openings and partial shade 
or shelter would produce better silvicultural results. 
3 While no experimental data are available bearing on the effect of direct heat on unlignifled seedlings, 
Dr. Paul Sorauer (Manual of plant diseases, tr. by F. Dorrance. Ed. 3, v. 1, illus. [Wilkes-Barre, Pa. 
1914-1922]) states that a temperature of 104 to 122° F. causes death of plant leaves by burning. Prof. J. W. 
Tourney and E. J. Neethling (Some effects of cover over coniferous seed beds in southern New England, 
Yale Univ., School Forestry Bui. 9, 39 p., illus., 1923) record having obtained surface temperatures up 
to 130° F. which caused death-foraging lesions on the unlignifled seedling stems. The author has observed 
similar results with Engelmann spruce in the greenhouse at temperatures between 110° and 120° F. 
96462—24t-8 
