But when sawlogs or other large products are being grown, timely 

 thinnings are desirable. In this study, the heaviest thinnings not only pro- 

 duced the fastest diameter growth but also concentrated it on selected crop 

 trees. The heavy thinnings will give comparatively early production of 

 large poles, piling, and sawlogs. It is of interest that the best rate of 

 growth was around 2. 5 inches in 10 years even on widely spaced and 

 heavily thinned plots where trees had more than half their height in live 

 crown. This is a bit short of the oft-advocated goal of 3. inches of 

 diameter growth in 10 years. 



To stimulate diameter growth, thinnings must be heavy (fig. 12). 

 However, when heavy thinnings are made, volume growth per acre is re- 

 duced. During the 5 years between cuttings, the heavily thinned plots in 

 this study forfeited 3 cords of pulpwood growth while gaining only an 

 extra 0. 3 5 inch of diameter growth. 



Management of Longleaf Plantations 



A 100-acre longleaf pine plantation was established in 1934-35 on 

 the Johnson Tract for a study of spacing, prescribed burning, pruning, 

 and thinning. 



On 60 acres, seedlings were planted at rates of 250, 700, 1,150, 

 1,600, 2,150, and 2,500 per acre. This part of the plantation has been 

 protected from fire. On the other 40 acres, seedlings were planted at 

 only four rates--250, 1,150, 1,600, and 2,500 per acre. At 3 years and 



Figure 12. --Increment cores taken from the 8 by 8 loblolly plantation 

 when the trees were 25 years old. Heavy thinning was necessary to boost 

 diameter growth. Light thinning merely prevented a decline. (Photo by 

 Louisiana Forestry Commission) 



AGE 20 YEARS: 



FIRST THINNING ~"X 













HIEAVY THINNING 







J LIGHT THINNING 



- 17 - 



