FOREST SERVICE. 391 



of seedlings in different light intensities varying from deep shade to 

 almost full sunlight. Light readings were taken at each station 

 hourly through the day on several clear daj's in July and October. 

 The readings at all the stations were as nearly simultaneous as pos- 

 sible. Seedling counts are made at each station yearly in order to 

 determine the rate of loss. Each count is accompanied by careful 

 notes in regard to the condition of the seedlings and any possible 

 disturbing factors. Periodic measurements of temperature, evapo- 

 ration, and soil moisture are made at each station to ascertain any 

 inlluence which might be due to these factors. It is known that 

 yellow-pine seedlings in certain situations do not usually survive 

 more than a few years, but it is not known whether their death is 

 due to lack of light or to other causes, and it is just such problems 

 which will be solved by the actual light-measurement experiments. 



A detailed study of conditions under which reproduction of yellow 

 pine takes place in the Southwest was completed on the Coconino 

 Forest. The problem of securing natural reproduction of this species 

 is the most important silvicultural problem of the region. The con- 

 clusions drawn from this study are as follows : 



The climatic conditions in this region during the average year are 

 extremely unfavorable to the establishment of seedlings. The 

 greatest mortality results from drought and frost during the first 

 season's growth. The effects of drought are more serious during 

 and immediately before germination. Of the artificial factors afl'ect- 

 ing reproduction the most important are cutting, disposal of brush, 

 grazing, and fire. Of these the most important factor is cutting. 

 As a rule no reproduction can be expected after a heavy cutting. 

 The cause of this is to be found not so much in the reduction of the 

 seed supply as in the removal of the influence exercised by the forest 

 upon pnysical conditions, especially temperature and evaporation. 

 Tlie first consideration in marking timber for cutting where repro- 

 duction is unsatisfactory should be to leave sufficient stand to secure 

 the best possible forest conditions. Usually this provision will also 

 insure a sufficient seed supply. Defective trees, whether "black 

 jack" or old yellow pine, standing in a large opening should be left 

 unless infested by insects or fungous diseases which would endanger 

 the remaining stand. The number of yellow pine to be left must 

 naturally vary with the character of the stantl, exposure, and soil. 

 In areas where there is a sufficient amount of immature growth to 

 afford good wind protection only a sufficient number of yellow pine 

 need be left to insure an adequate seed suppl3^ From four to five 

 seed trees per acre are sufficient. Sound, fidl-crowned trees standing 

 in the more open situations make the best seed trees. Areas in 

 which practically the whole stand is mature should be cut as lightly 

 as possible, with the object of returning for a second cut as soon as 

 reproduction has taken place. When natural conditions for repro- 

 duction are exceptionally unfavorable, as on deep cintler soils, exposed 

 situations, and regions of low precipitation, it is necessary to leave 

 a denser stand than where conditions arc more favorable. When- 

 ever possible, advantage siiould be taken of tiie fact that the greatest 

 amount of reproduction usually starts under the immediate influence 

 of the mother tree, where the light intensity is frequently too low 

 for seedlings to develop noimally in later life. An area on which a 

 good crop of seedlings has sprung up beneath the trees should be 



