16 



BULLETIN 244, U. S. DEPARTMENT OP AGRICULTURE. 



Age 20 Years 

 (800 Trees Per Acre) 



Age33Years 

 (580 Trees Per Acre) 



Valley region the first general period ends somewhere between the 

 ages of 40 and 50 years, depending upon the local situation; in the 

 central Atlantic coast belt apparently between 55 and 70 years. 

 Figure 6, showing progressive stages of natural thinning and crown, 



classed according to 

 age, represents actual 

 numbers of trees and 

 outlines of crowns as 

 the}' existed in four 

 fully stocked stands 

 in Arkansas measured 

 for growth and yield. 

 The 20-year-old stand 

 contained 800 trees per 

 acre; the 33-year-old 

 stand, 580 trees; the 

 42-year-old stand, 400 

 trees; and the 52-year- 

 old stand, 320 trees 

 per acre. 



Shortleaf pine shows 

 progressive changes in 

 the character of the 

 forest canopy other 

 than the mere reduc- 

 tion in number of trees. 

 These changes are well 

 illustrated in figure 6 

 for stands from 20 to 

 50 3 r ears old. In early 

 life the tree crowns are 

 approximately circular 

 in outline and closely 

 approach each other, 

 leaving very little un- 

 occupied space. At 

 the age of 50 years, 

 however, the tree has 

 become less tolerant, 

 the crowns are quite 

 irregular in outline, and crown isolation leaves relatively large light 

 spaces in the canopy. The slow rate of natural thinning after about 

 50 years undoubtedly is accompanied by relatively small changes in 

 the tolerance of the tree. The climax of lateral growth or spread 

 of the branches characteristic of the species seems to be closely ap- 



Age4-2 Years 

 (400TreesPerAcre) 



Age52Years 

 (320Trees Per Acre) 



Fig. 6.— Progressive change in tree density by natural thinning 

 in pure even-aged stands of shortleaf in Arkansas: T>, Dominant 

 classes; I, intermediate; S, suppressed classes. Areas. 33 by 66 

 feet. (Drawn from actual stands.) 



