UNITED STATES DEPARTMENT OF AGRICULTURE 



DEPARTMENT BULLETIN No. 1105 



Washington, D. C. 



April 27, 1923 



NATURAL REPRODUCTION OF WESTERN YELLOW PINE 

 IN THE SOUTHWEST. 



By G. A. Pearson. Silviculturist, Fort Valley Forest ■ Experiment Station, 



Forest Service. 



CONTENTS. 



Page. 



Purpose of study 1 



Review of previous investigations _ 2 



Recent developments in the study 4 



Factors influencing reproduction 9 



Seed supply 9 



Climate 22 



Soil 29 



Herbaceous vegetationl 38 



Page. 

 Factors influencing reproduction — 

 Continued. 



Cutting 56 



Brash disposal 92 



Grazing 115 



Miscellaneous enemies 133 



Summary 135 



Literature cited 142 



PURPOSE OF THE STUDY. 



A forest in which cutting is not followed by reproduction is 

 doomed to ultimate extinction. In some regions planting or direct 

 sowing will prove an efficient and economical means of restocking. 

 In the western yellow pine forests of Arizona and New Mexico slow 

 growth and high costs, as a general rule, render artificial reforestation 

 impractical; therefore restocking must be accomplished by natural 

 means. Because of the abundance and great economic importance 

 of western yellow pine, the difficulties attending its natural regenera- 

 tion present the most vital silvicultural problem in the Southwest. 

 Young growth is abundant in many localities of this region ; but in 

 the localities of most extensive lumbering operations it is generally 

 deficient, even where seed trees were left. The purpose of the 

 study on which this report is based is to determine what measures 

 are necessary to secure natural reproduction. Because the problem 

 is particularly acute on the Coconino and Tusayan National Forests 

 in northern Arizona, where several large mills have been in operation 

 for 30 years, investigations have been concentrated there. Although 

 these investigations do not cover every individual case which may be 



904°— 23 1 



