154 



INTERMEDIATE CUTTINGS THINNINGS 



technically known as a differentiation into crown classes and 

 standard crown classes are recognized. (See Figs. 58 and 59.) 

 Classification into Crown Classes. The classification here- 

 with given is that favored by the Society of American For- 

 esters. See Appendix. 



3000 



2700 



2400 



I 2100 



PH 1800 



1500 



8 



| 1200 

 fe; 900 



300 



20 



30 



70 



100 



40 50 60 

 Age in Years 



x Curve plotted from data on p. 21, Bulletin 13, United States Department 

 of Agriculture, entitled " White Pine under Forest Management". 



Curve plotted from data on p. 41, Bulletin 244, United States Department 

 of Agriculture, entitled " Life History of Shortleaf Pine". 



Curve plotted from data on p. 24, Bulletin 24, United States Department 

 of Agnculture, entitled " Cottonwood in the Mississippi Valley". 



FIG. 57. 



Curves showing the reduction in number of trees per acre due to natural 

 causes with increase of age for stands of cottonwood, shortleaf pine and white 

 pine on Quality I soils. 



