1150 
Journal of Agricultural Research 
Vol. XXVIII, No. 11 
meter square, away from all roots. The records, except those of soil moisture, 
were taken at 5 p. m. each day from July 12 to August 31. A summary of the 
data obtained is given in Tables I and II. 
Table I.— Physical conditions within the forest and on large clearings 
(Summaries of measurements July 12 to August 31, 1919) 
Air temperature 
Relative 
humidity 
5 p. m. 
Daily 
evapora¬ 
tion 
Soil tem¬ 
perature 
at depth 
of 6 
inches 
Soil 
moisture 
at depth 
of 6 
inches 
Stand conditions 
Average 
maxi¬ 
mum 
Average 
mini¬ 
mum 
o 
°F. 
Per cent 
Cc. 
°F. 
Per cent 
Open. 
87.7 
39.5 
30.7 
35.3 
63.2 
•31.6 
^36.7 
One-third cover____ 
85.3 
44.3 
33.0 
26.9 
59.9 
°23.J> 
6 28.1 
Uncut.. 
80.3 
46.2 
35.0 
16.0 
54.7 
® 28.0 
6 32.6 
« July measurements. 
h August measurements. 
Table II.— Daily march of air temperature in the forest and on large clearings 
(Thermograph records for August in degrees Fahrenheit) 
Location 
A. M. 
P. M. 
2 
4 
6 
8 
10 
12 
2 
4 
6 
8 
10 
12 
In open.... 
In forest. 
42.7 
50.7 
40.4 
47.9 
39.5 
46.0 
50.4 
47.6 
64.5 
57.7 
76.7 
67.4 
82.4 
74.1 
83.3 
76.1 
78.5 
73.6 
61.2 
65.9 
51.0 
56.6 
46.1 
53.9 
The records in Table I show that the high points of air and soil temperatures 
in the open average from 7 to 8 degrees higher than within the uncut forest, 
and that the range in air temperature in the open is 48.2 degrees but only 34.1 
degrees in the forest. These differences, accentuated by a lower humidity and 
greater evaporation, which naturally intensify the effect of drought on exposed 
surfaces, are factors which must be carefully weighed in providing suitable 
environments for seedling establishment of western white pine or other moisture- 
loving species. It should be stated that the slightly lesser soil moisture observed 
under the forest than on the open plot is considered due to root activity under 
the forest, for every part of the soil under the mature forest comes within reach 
of certain roots, whereas on the open plot where no trees exist, root competition 
is eliminated. In neither case, forest or open, did soil moisture conditions show 
any material difference or appear critical. The injurious effects of the exposure 
are expressed rather by greater evaporation and presumably much higher rates 
of transpiration, higher soil temperatures, or greater weed and grass competition 
on the open area than elsewhere. 
There is other evidence that complete openings one-quarter mile or more in 
extent render the site very unfavorable to natural establishment of hemlock and 
cedar and Engelmann spruce ( Picea engelmanni ), and somewhat precarious for 
white pine seedlings. This is expressed by the disappearance in such locations 
of many of the typical moisture-loving plants which usually grow underneath 
and among the white pine stands, such as Coptis trifolia y Cornus canadensis , 
Aralia nudicaulis, Asarum caudatum , Circaea pacifica, Claytonia perfoliata , 
and Galium horeale; and the appearance of species less dependent upon soil 
