316 



FORESTRY AND IRRIGATION 



July 



THREE GRADES OF THINNING AND A LIGHT INCREMENT CUTTING ( IV 



THE AVERAGE TREE IN EACH SAMPLE PLOT. 



SECTIONS FROM 



1882 

 x 



THINNINGS. 

 i>$7 1892 



O X 



1897 



I 



From the fiftieth or sixtieth year on 

 the thinning should be about the C 

 grade. 



At the beginning of the last third of 

 the rotation, or about the seventy-fifth 

 year, the trees should be so formed and 

 in such relation to each other that no 

 more real thinnings are necessary. From 

 this time on all the increment should be 

 in the final stand. 



Stands which are in bad condition 

 through lack of early thinning or other 

 causes should be successively thinned to 

 the C grade, as they recuperate best by 

 this method. 



In these experimental results no men- 

 tion has been made of selection thinning. 

 The only figures which deal with this 

 subject known to the writer are those of 

 Dr. Wimmenauer in Giessen. In 1894- 

 '95 he began the comparison with ordi- 

 nary B and C thinnings with the Borg- 

 greve method and edaircic par le haul 

 or ordinary selection thinning. Borg- 

 greve's method takes out that part of 

 the dominant stand which is merchant- 

 able in the expectation of developing 

 dominant trees from the suppressed 

 members of the forest. 



After the first five-year period, in 



