20 



SHORTLEAF PINE IN VIRGINIA 



forty-five years old, timber is produced at the lowest cost by cut- 

 ting when the stand is about this age (see tables 12 and 17). 

 Under ordinary conditions, the stand would be cut for lumber, and 

 not thinned, at this period. (Plate V). 



This method of thinning crowded stands is based on the 

 average crowded stand. 



Typical Stands. Table I shows approximately the average 

 number of trees of each diameter from four inches up, which were 

 found in irregularly thinned stands growing under average condi- 

 tions. This table is approximately correct for the average of a 

 number of stands, but any individual stand at a given age will 

 probably show considerable variation from it, both in the total 

 number of trees per acre and in the number of trees in each class, 

 since slight differences in the quality of the soil affect the number 

 of trees to the acre at any age, and the degree of thinning in- 

 fluences both the number of trees and their size. It shows, how- 

 ever, the rapid elimination of the smaller trees, which are the ones 

 which should be chiefly removed in the thinnings, and it will serve 

 as a guide to indicate about the number of trees of each size which 

 should be taken out at each thinning. The stands which have been 

 grouped as thinned stands in some cases were undoubtedly natur- 

 ally thinly stocked and their density has been further affected by 

 artificial thinnings. For this reason the favorable conditions of 

 these stands can not be entirely ascribed to thinnings. 



TABLE 1. 



Approximate number of trees four inches and over in diameter to the acre 

 in unsystematically thinned stands of shortleaf pine (the twenty-year- 

 old stand is unthinned}. 



