46 LIGHT IN RELATION TO TREE GROWTH. 
FOREST SERVICE INVESTIGATIONS. 
G. A. Pearson took a number of light readings, by means of Clem- 
ents’ photometer, on several species of forest trees at the Coconino 
Forest Experiment Station near Flagstaff, Ariz., in 1909, and on the 
Wallowa National Forest in northeastern Oregon in 1907. 
At the Coconino Forest Experiment Station, at an elevation of 
7,200 feet, on a limestone formation, he found the following light 
values for western yellow-pine seedlings at five different places: 
Average | 
Average 
Condition of seedlings. light || Condition of seedlings. light 
intensity.|| intensity. 
IRAP SS ese ee Ree Drea tenn a Seeiis cete Ee 0:3851|(GGOOd sr She ieee meee ae ee ees 0.570 
AT oo Chartie I  e a etna eae 309 ORE eS re ae Bonen wee eM Nia eens f . 630 
GOO dees Bee ee eee eee eee as -414 
In a sapling stand of western yellow pine 24 years old, on rocky, 
volcanic soil, elevation 7,300 feet, readings around an old, full- 
crowned tree at the inner limit of thrifty sapling growth gave the 
following hght values: 0.579, 0.547, 0.379, 0.828. Readings in a group 
of suppressed saplings in a near-by stand gave values of 0.088 and 
0.026. 
From these observations it appears that the seedlings of western 
yellow pine grow fairly well in a light intensity of from 0.309 to 
0.414, while the older saplings evidently require a light intensity of 
0.328. 
In a thick stand of white fir (Abzes concolor) saplings from 4 to 12 
feet high under Douglas fir, white fir, and western yellow pine, on a 
steep, very rocky south slope, he obtained the following light values: 
ae Light ane Light 
Condition. intensity. | Condition. intensity 
| 
SUPP TOSS CLE eyo ses ros re eat heen 8 O1020):|| A@oodeyayasccc eee se ace eae eee eee 0. 068 
(OVO US eee Heeger enamel ee MA Ar re . 048 dB Xo eee ty een Sey Seen aes sate ate ait go iat 027 
1D) Oe Ress a ps tae iy Be . 028 
In a stand of Douglas fir (Pseudotsuga taxifolia) saplings from 
4 to 6 feet high under western yellow pine, aspen, and Douglas fir, on 
a gentle, northwesterly slope, at the edge of draw, with rocky but 
fresh soil, he obtained the following values: 
ie | Light | Light 
Condition. | Pitensie| Condition. jngancity: 
POSTS rye Mera ae UN ven. Sie! a, once | 6:049:| (Goodies . ace ae ee es | 0.192 
Faint; Weenie aa ee ee ou | 097 | Dock ee ie eee "133 
