REPRODUCTION OF WESTERN YELLOW PIXE. 93 



or pulled. This opinion is based upon the observation that in old 

 cuttings, where reproduction is generally deficient, more seedlings 

 are usually found along logs and tops than in the open. The ex- 

 planation generally accepted is that the projecting branches pro- 

 tect young seedlings against excessive sun and wind, and that the 

 leaf litter and twigs falling on the ground form a mulch which is 

 effective in conserving soil moisture. In order to test this theory, 

 experiments were initiated in 1908 and have been carried on inter- 

 mittently until the present time. 



The earlier investigations were confined to a test of the effects 

 of scattering. Progress of reproduction was compared on plots 

 covered with scattered brush and on plots having no brush cover. 

 Records of seedling establishment were supplemented by studies of 

 physical conditions, particularly the changes in the brush cover 

 from year to year, and the effect upon soil moisture. An experi- 

 ment initiated in 1908 has given negative results with reference to 

 seedling survival, whereas one initiated in 1914 shows a decided 

 advantage in favor of scattered brush. Later investigations have 

 shown that this discrepancy is due to the fact that we are dealing 

 with two sets of conditions. The essential point of difference is 

 that in the 1908 experiment a dense stand of bunch grass was allowed 

 to grow unhampered even by grazing throughout the entire period 

 of 13 years, whereas in the 1914 experiment the herbaceous vegeta- 

 tion was eliminated at the start by plowing. Determinations of 

 soil moisture in 1909. 1912. 1919. and 1920 show a consistently higher 

 moisture content underneath the brush than in open situations. The 

 investigations are presented in chronological order. 



1908 Experiment. 



Seedling survival. — Brush was scattered on an area of 126 acres in 

 the cinder region about 8 miles east of Flagstaff. The branches cut 

 from the felled trees sufficed to cover less than half the total ground 

 surface. Since this area is typical of the most extreme drought con- 

 ditions in the yellow-pine type, it was anticipated that the effects of 

 brush upon reproduction would be decisively demonstrated. After 

 12 years, however, no appreciable difference between brush-covered 

 and open spots could be discerned. In 1909 a considerable number 

 of seedlings started both in the brush and outside, but in 2 years 

 nearly all had disappeared. Very few seedlings have started since 

 1909. Even in 1919, when a bountiful seed supply and ideal condi- 

 tions for germination resulted in abundant reproduction generally 

 on the Colorado Plateau, no seedlings appeared on this area, for the 

 reason that the 1918 seed crop was almost a total failure in this par- 

 ticular locality. Sample plots from time to time have yielded re- 



