2 BULLETIN 1105, U. S. DEPARTMENT OF AGRICULTURE. 



encountered in the yellow pine type of the Southwest, they have 

 sought to evolve broad principles which will serve as a basis for the 

 solution of reproduction problems under a wide range of conditions. 



REVIEW OF PREVIOUS INVESTIGATIONS. 



In 1904 Leiberg (14) 1 wrote regarding western yellow pine on 

 the San Francisco Mountains Forest Reserve, now the Coconino and 

 Tusayan National Forests: 



Apparently there has been an almost complete cessation of reproduction over 

 very rarge areas during the past 20 or 25 years, and there is no evidence that 

 previous to that time it was at any period very exuberant. The low repro- 

 ductive ratio is due to various causes, some depending on the operation of 

 natural agencies, other on human intervention. Those originating in natural 

 agencies manifest themselves chiefly in deficient seed production, a factor 

 which strikes at the very root of existence of the species ; those due to the acts 

 of man depend on the destruction of the individual trees. 



Natural reproduction of western yellow pine has been the foremost 

 subject of investigation at the Fort Valley Experiment Station since 

 the establishment of the station in 1908. 2 The initial results of 

 this study were presented by the writer in 1909 {15). In the same 

 year a series of sample plots was established on the Coconino and 

 Tusayan National Forests for the purpose of maintaining continuous 

 records of the progress of reproduction as well as of growth on areas 

 cut according to the silvicultural practice then prevailing. In 1910 

 and 1911 additional plots were established on the Datil, Santa Fe, 

 and Gila National Forests in New Mexico. In 1913 another series 

 of plots, involving three methods of cutting, was established on the 

 Coconino. The method of establishing the plots has been described 

 in detail by Woolsey (27). A discussion of results obtained from 

 records of the first five-year period on the Coconino and Tusayan 

 plots was published by the present writer in 1918 (18). 



The conclusions drawn from all of the studies by the Fort Valley 

 Experiment Station up to 1918 are summarized in the following 

 paragraphs. It should be noted that some of these conclusions, par- 

 ticularly with reference to forest cover, brush disposal, and grazing, 

 have been modified and developed as a result of more recent investi- 

 gations. 



1 The italic figures in parenthesis refer to the bibliography in the back of the bulletin. 



2 Grateful acknowledgment is due to members of the staff of the Fort Valley Experi- 

 ment Station. Among those who at different times have been identified with this study 

 are H. D. Burrall, H. H. Greenamyre, J. S. Boyce, C. F. Korstian, E. W. Nelson, Hermann 

 Krauch, and F. W. Haasis. Especially valuable assistance has been rendered by Mr. 

 Haasis, who during the last two years has made most of the seedling counts, and has 

 taken an active part in the soil studies and in the compilation of data. J. O. Veatch, 

 of the Bureau of Soils, has made a most valuable contribution to this investigation 

 through his soil surveys and other soil studies, all of which have aided materially in 

 handling this phase of the reproduction problem. 



