234 JOURNAL OF FORESTRY 



Stands in which the trees grow, and on this general basis there would 

 be a very wide divergence in tolerance between yellow pine and 

 spruce. That there is not, however, a very wide difference in light 

 requirements of the various species is indicated by the fact that occa- 

 sional yellow pine seedlings appear in the densest stands of Douglas 

 fir; likewise lodgepole reproduction is frequently abundant in spruce 

 stands where deficient soil moisture opens the stand slightly. 



For germination either in the greenhouse, nursery, or field, we 

 may state it as an established fact that light is not required. Light 

 itself cannot affect the seed or seedling which is covered by soil or 

 litter, and can act only through the agency of soil temperatures. With 

 the possible exception of Engelmann spruce and balsam, germination 

 of our trees occurs in the field under the densest shade which is likely 

 to be encountered. That Engelmann spruce germination should be 

 influenced by light is plainly due to the low temperature of the soil. 

 which in the dense spruce forest may be Httle above 32° F. at mid- 

 summer. 



While any of our species will germinate with a very small ration 

 of light, and the seedlings survive for some time on the food furnished 

 by the endosperm, there is always much more germination in shaded 

 places than survival after a year or two. Other factors than shading, 

 of course, tend to destroy the seedlings, but this is one of the most 

 important. 



Pearson,* by measurements with the Clements photometer, has 

 determined that good growth of yellow pine seedlings occurs with a 

 relative light intensity of .414; of Douglas fir with about .125, and 

 white fir about .027. Notestein,^ in a stand mainly of Douglas fir, 

 found seedlings of both Douglas fir and Engelmann spruce most 

 numerous where the light intensity was about .100 and concluded (1) 

 that there was abundant light for these seedlings anywhere in the 

 Douglas fir stand, and (2) that the lack of them in openings was 

 explained by a deficiency of soil moisture. Permanent sample plots 

 in lodgepole pine show that, while lodgepole seedlings start in great 

 numbers where the average light intensity is .350 or less, they only 

 survive in considerable numbers where the intensity is above .400. 

 On the other hand, with an intensity of .750 germination is greatly 

 reduced by drying of the surface soil, but the survival and rate of 



< Pearson, G. A., contributor. See footnote 9, p. 236. 



5 Notestein, Frank B., Forest Examiner. Unpublished report, 1913. 



