REPRODUCTION OF WESTERN YELLOW PINE. 



63 



sharp drop on site 1. while site 2 continued to rise until a month later. 

 The rise in both graphs in October is attributed to a slowing-up of 

 plant activity because of cool weather. Nearly all herbaceous vege- 

 tation was either mature or was killed by frost early in October. 



The above experiment was repeated in 1920 on a similar site about 

 one-fourth mile distant from the first, but in a denser stand. The 1919 

 experiment was in a lightly cut stand bordered on the south, about 

 100 yards distant, by a heavier cutting. In 1920 a site was selected 

 in the midst of a virgin stand. A group of five yellow pines 20 to 30 

 inches in diameter was uprooted the preceding fall by a wet snow, 

 the weight of which caused the trees to fall in different direction-. 

 as shown in Figure 10. This created an opening 160 feet wide by 

 400 feet long, the bases of the fallen trees being a few feet north and 

 east of the center. The herbaceous vegetation was similar to that 

 of the 1919 site, excepting that only a small amount of lupine ap- 

 peared during the summer. As in 1919. the soil samples were taken 

 well outside the heavily littered and shaded areas. No samples were 

 taken within 10 feet of the branches or trunks of the fallen trees. 

 All things considered, this experiment would be expected to show a 

 sharper contrast between the areas of live tree roots and those of 

 dead tree roots than did the 1919 experiment. Because of greater 

 density of the stand surrounding the opening, the contrast in root 

 activity was probably greater in this experiment than in that of 1919. 

 Subnormal rainfall in 1920 served to accentuate this contrast. Close 

 grazing eliminated to a large extent the effect of herbaceous vegeta- 

 tion, and therefore it is believed that any differences in soil moisture 

 may be attributed mainly to differences in the activity of tree roots. 

 In the 6-inch samples, however, direct evaporation also plays an im- 

 portant part. Since this is least near the standing trees, on account 

 of the partial shade, it tends to minimize the effect due to differences 

 in root activity. 



Table 17. — Effect of cutting upon soil moisture. 1920. 



Depth and location. 



Wilt- 

 ing 

 coeffi- 

 cient. 



Available soil moisture in percentage of dry weight. 



May 



17. 



June 



June 



July 



4. 



19. 



5. 



5. 7 



3.2 



1.3 



9.0 



2.9 



-0.7 



10.2 



4.5 



5.3 



9.2 



6.7 



7.4 



5.3 



1.9 



4.1 



5.9 



2.1 



-0.1 



11.0 



8.3 



9.6 



9.9 



8.7 



8.7 



July 



14. 



Aug. 



Sept. 



9. 



1. 



6.8 



2.4 



6.7 



3.2 



11.4 



3.7 



11.6 



5.0 



6.2 



2.1 



1.8 



-0.2 



10.5 



6.5 



^.9 



6.0 



Oct. 



Depth 6 inches: 



A. West of experiment station — 

 Area of root action (near group 

 of living trees) — 



We^t 



North 



No active roots (near group 

 of fallen trees,) — 



South 



West 



Depth 12 inches: 



Near group of living trees- 

 West 



North 



Near group of fallen trees- 

 South 



West 



11.6 

 11.6 



11.5 

 10.3 



14.0 

 14.0 



11.6 

 11.9 



8.9 



8.6 



10.7 



9.9 



7.0 



10.8 

 11.2 



0.0 

 -0.5 



0.4 

 2.8 



2.3 

 0.3 



4.8 

 6.2 



-0.5 

 1.9 



4.0 

 4.5 



1.6 



6.9 

 5.1 



