1458 A NATIONAL PLAN FOR AMERICAN FORESTRY 



Thinning consists in removing from dense stands of timber a certain 

 fraction of the trees in order that those which remain may grow more 

 rapidly. Unlike weeding, the thinning operation does not especially 

 concentrate on inferior species or specimens, but removes good trees 

 simply to reduce the stand density. 



Thinning not only stimulates growth but may serve to improve the 

 quality of the product. It has been found that the most desirable 

 quality of wood in certain hardwood species is produced when the 

 growth rate is maintained within certain well-defined limits. Through 

 thinning the forester may maintain a density of stand which will result 

 in the desired width of annual growth rings and thus insure the de- 

 sired strength or other technical qualities in the wood. 



When the trees removed in thinning young stands can be marketed, 

 the thinning may salvage material that would ordinarily be killed out 

 in the normal struggle for existence. Thinning may thus make pos- 

 sible an early reduction of the forest investment, a result which is 

 especially desirable in plantations. Wood supplied from thinnings 

 may meet industrial needs for small-sized material, also, and thus 

 make unnecessary the clear cutting of immature stands which under 

 usual practices would be sacrificed for such purposes. 



In certain types, of which lodgepole pine is a striking example, 

 natural reproduction forms such a dense thicket that stagnation of 

 growth results. Here a thinning operation even of unmarketable 

 material may pay dividends by causing increased growth, especially 

 if mechanical means can be developed for opening up the overdense 

 stands of small trees. 



At the present time very little of America's immature forest is 

 systematically thinned; in Europe the practice is almost universal. 

 Were America's forests more completely developed by roads, and were 

 American forest owners and users better educated in' the care of forest 

 land, it would undoubtedly be recognized as profitable to do much 

 more thinning. 



An example of this type of cultural operation may be found on the 

 property of the Superior Pine Products Co., near Fargo, Ga. In the 

 last 3 years this company has thinned more than 2,500 acres of 15- 

 to 20-year-old stands of longleaf and slash pine. The number of trees 

 per acre has been reduced from between 600 and 1 ,200 to an average 

 of 250. The operation cost about 50 cents per acre, but the company 

 expects to realize a great deal more than that amount through acceler- 

 ated growth and increased turpentine yield. 



Pruning the lower limbs of valuable species like northern white pine 

 in New England in order to produce higher-grade lumber has been 

 found in some cases to increase the value of the pruned trees by $35 

 per 1,000 board feet. Pruning is recommended as a desirable prac- 

 tice hi plantations and natural stands where improved quality will be 

 so strikingly reflected in stumpage value. To be profitable and 

 effective, however, pruning must be done judiciously. To keep the 

 cost within reason pruning should be restricted to a selected number 

 of the best and most promising stems, probably not more than 250 

 per acre in dense plantations. To be effective pruning should extend 

 to the full length of the butt log and should be done when the trees 

 are not more than 5 inches in diameter. This can usually be accom- 

 plished to best advantage in 2 or 3 operations at intervals of 3 to 5 

 years. 



