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 r 



2700 



2400 



o 2100 



< 



p, 1800 



<u 



^ 1500 



S 1200 



B 



•^ 900 



600 



300 



10 



20 



30 



40 



Age 



50 60 



in Years 



70 



80 



90 



100 



X Curve plotted from data on j). 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 Agriculture, 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. 



