REPRODUCTION OF WESTERN YELLOW PINE. 97 



Although the experiment on the cinder area has been disappoint- 

 ing as a decisive demonstration of the effects of brush disposal upon 

 reproduction, it has yielded valuable information of a more general 

 character. First of all, it shows that under protection against fire 

 and unregulated grazing, reproduction, though extremely slow, 

 will eventually succeed even on such adverse sites as this one. Since 

 about three-eighths of the seedlings were on the ground before the 

 cutting, the importance of preserving advance growth on such sites 

 becomes evident. Xotes on the condition of the brush from time to 

 time yield a valuable record of the rate of disintegration and other 

 changes. 



Progressive changes in the character of the cover. — From the time 

 the branches are placed on the ground until they are decomposed, 

 involving a period of from 15 to 20 years, the cover undergoes a series 

 of successive changes which may be assumed to be accompanied 

 by corresponding changes in the effect upon reproduction. These 

 effects may range from beneficial to positively detrimental. Several 

 more or less distant periods or stages of disintegration have been 

 recognized. In green brush-the bowed form of the branches usually 

 prevents them from lying flat, and consequently they form a screen 

 from a few inches to 2 feet or more above the soil surface. This 

 applies particularly to scattering. In pulled tops, the lowermost 

 branches are pressed down, while the others project into the air. 

 The density of the screen depends upon the density of the branches 

 and foliage. Plate XV, Figure 1. and Plate XVIII, Figure 1, give 

 an idea of the character of the cover during first and second sea- 

 sons. Usually the sun's rays are only partially excluded, and the 

 air circulates freely underneath the cover. In this stage falling 

 seeds readily penetrate the cover, excepting where it is unusually 

 dense. Germination is favored by the conservation of surface soil 

 moisture : but where the cover is dense damping off may become 

 serious, and subsequent development is retarded by lack of sunlight. 

 If not more than half the sunlight is cut off, most of the seedlings 

 should survive. Heavy snows tend to flatten out the branches and 

 bring the entire screen closer to the ground. Here again density 

 is important. If the cover is close, the snow tends to pile on top, 

 pressing down the branches and crushing seedlings which may be 

 underneath, whereas if the brush is more open the snow sifts through, 

 settles underneath, and thus helps support the load. During the 

 second season the boughs will be closer to the ground, and some 

 leaf tufts will be matted down ; all the leaves will be brown, although 

 mostly still remaining on the stems. On the whole, the character 

 of the cover is not very different from that of the first season. But 

 a new factor enters in the form of competing vegetation. When 

 904°— 23 7 



