LIFE HISTORY OF SHORTLEAF PINE. 



17 



proached at about the age of 50 or 60 years on the best sites and 

 70 to 90 years on the poorer sites. In respect to the number of 

 trees per acre at these ages, shortleaf somewhat exceeds longleaf 

 and notably surpasses loblolly on similar qualities of site. At ages, 

 ranging mostly from 175 to 225 years, natural thinning of stands, 

 due to old age and overmaturity, goes on at a more rapid rate. This 

 is closely associated with the incoming of the new generation and the 

 sudden and rapid increase in numbers per acre. 



The number of trees per acre in well-stocked stands decreases as 

 the quality of the site improves. At 20 years, well-stocked stands 

 in the Arkansas region have usually from 1,000 to 1,300 trees per acre; 

 in North Carolina, 1,400 to 1,800; and in central New Jersey, 1,800 

 to 2,400. In general, this regional difference holds good for several 

 decades; so that at 50 years well-stocked unthinned stands have 

 approximately 300, 355, and 500 trees per acre, respectively, in the 

 above three regions. The relation of the density to the quality of 

 situation, both in one locality and in widely separated regions, 

 appears to be constant and regular. The difference in densities in 

 normal or well stocked stands in North Carolina and Arkansas is well 

 shown by the contrast between Table 5 and Table 6. 



Table 5. — Number of shortleaf trees per acre in stands of different densities in Arkansas. l 



Age (years). 



Under- 

 stocked. 



Well 

 stocked. 



Over- 

 stocked. 



Age (years). 



Under- 

 stocked. 



Well 

 stocked. 



Over- 

 stocked. 



20 



840 



475 



290 



210 



170 



140 



100 



80 



80 



75 



1.130 



600 

 400 

 300 

 250 

 215 

 185 

 145 

 128 

 118 



1,540 

 1,000 

 550 

 400 

 325 

 280 

 250 

 185 

 175 

 160 



120 



75 

 70 

 65 

 65 

 60 

 60 

 60 

 55 

 55 



115 



110 

 105 

 102 

 100 

 100 

 100 

 98 

 95 



155 



30 



130 



150 



40 



140 



145 



50. 



150 



140 



60 



160 



140 



70 



170 



140 



80 



180 



140 



90 



190 



140 



100 



200 



135 



110 











i Based on measurements in 38 even-aged stands. The number of trees per acre vary quite widely in 

 each case in accordance with the quality of the situation, and the numbers should be considered approxi- 

 mate rather than exact. 



Table 6. — Number of trees per acre for well-stocked shortleaf stands in North Carolina. 1 



Age (years). 



20 

 25 

 30 

 35 



40 

 45 

 50 



Quality 



Quality 



Quality 



I. 



II. 



III. 



1,000 



1,635 



2,450 



675 



1,095 



1,880 



510 



765 



1,405 



410 



600 



1,045 



340 



500 



795 



280 



420 



655 



235 



355 



550 



Age (years). 



55 

 60 



65 

 70 

 75 



Quality 



Quality 

 II. 



200 



310 



165 



270 



140 



230 



120 



205 



100 



180 



90 



155 



Quality 

 IIL 



475 

 420 

 370 

 330 

 295 

 270 



1 Based on measurements of 80 sample plots; area, 21.6 acres. 

 92233°— Bull. 244—15 3 



