EEPKODUCTIOX OF WESTERN YELLOW PINE. 



61 



content than those taken on site 2, in the area near the felled trees. 

 The fact that this relation obtained on May 1 and on August 1, 

 when the soil in both situations was thoroughly saturated, suggests 

 that the soil in site 2 has a higher capacity for water than that of 

 site 1. However this may be, it is significant that this lead was 

 maintained through the most active growing period, and that it in- 

 creased during the periods of least rainfall, in June and September. 

 Table 16. — Effect of cutting upon soil moisture, 1919. 









Available soil moisture in percentage of dry weight. 







Wilt- 

 ing 

 coeffi- 

 cient. 





















Depth and location. 



Apr. 



June 



June 



July 



July 



Aug. 



Aug. 



Sept. 



Oct. 





2S. 



3. 



17. 



1. 



16. 



2. 



30. 



15. 



6. 



Depth 2 inches: 























Area of root action, near 























live trees — 























Northeast 



8.3 

 8.6 



7.8 



14.3 

 32.9 

 15.5 



19.2 

 38.9 

 26.6 



7.4 

 16.6 

 2.7 



1.9 

 5.1 

 5.6 



31.2 

 30.6 

 21.1 



24.3 

 32.2 

 22.5 



10.4 

 19.8 

 9.6 



7.9 



14.7 



XJnder crowns - . 





No active roots, trees feUed. 



"ii's' 



'"'22.'5 



Depth 6 inches: 























Near live trees — 























Northeast '. 



13.5 

 12.0 

 11.3 



11.9 

 12.3 

 17.1 



12.8 

 16.0 

 13.5 



6.5 



■"8.'2" 



2.2 

 4,3 

 5.6 



17.0 

 17.8 

 17.0 



15.3 



20.8 

 19.8 



5.4 

 7.4 

 7.7 



4.3 



4.4 



Under crowns 





No active roots, trees felled. 



"""6.T 



""is.'i 



Depth 12 inches: 























Area of root action, near 























live trees, northeast 



17.1 



9.7 



16.5 



7.9 



1.1 



13.4 



14.1 



5.0 



3.8 



48 



No active roots, treesfelled. 



14.8 



11.4 



10.7 



5.0 



5.4 



13.5 



12.9 



8.5 



6.4 



9.3 



Depth 24 inches: 























Area of root action, near 























live trees, northeast 



16.3 



15.3 



16.2 



20.4 





20.7 



20.3 



12.4 



11.4 



12.0 



No active roots, treesfelled. 



13.6 



10.3 



16.1 



IG. 1 



'"is.'e' 



17.2 



16.4 



19.0 



14.5 



16.7 



In the 12-inch series, site 1 certainly is not handicapped at the 

 beginning of the season. On June 1 and June 15 (heavy rains fell 

 through May) it was 6 per cent and 3 per cent, respectively, above 

 site 2 ; but by the end of the month, after active growth had been in 

 progress for nearly a month with no rainfall, it had fallen to 4 per 

 cent below site 2. On August 1, after prolonged heavy rainfall, site 

 1 again takes the lead, but loses it with the decline in precipitation 

 during the latter part of August and September. These graphs fur- 

 nish a striking illustration of the power of tree roots to reduce soil 

 moisture. Although the areas occupied by living tree roots had a 

 considerable margin at the beginning of the season, it became drier 

 by the end of June and in September than the other area, in which 

 there were no active tree roots. The 12-inch samples probably show 

 the effect of tree roots better than any other depth, since they repre- 

 sent the level of maximum root activity, and also are below the in- 

 fluence of direct surface evaporation. According to the investiga- 

 tions of Rotmistrov (22), the effect of direct evaporation is practi- 

 cally limited to the surface 12 inches of soil. Buckingham {3) finds 

 that under arid conditions, such as prevail in the Southwest, the soil 

 automatically protects itself against extreme drying by forming a 

 natural mulch on the surface. 



