CHAP, x.] Stimulation of Increment 229 



5 to 15 ft. in height. On the removal of the standards the 

 blanks thus formed in the new crop can easily be filled up 

 artificially, and may be advantageously utilized for the forma- 

 tion of mixed forests by the introduction of other species. 



Actual measurements of crops thus treated are not yet 

 available for comparison with the yield-tables published for 

 pure forests ; but the approximate data already given may be 

 contrasted favourably with the more accurate information con- 

 tained in these latter. According to v. Baur, pure forests of 

 Spruce of 120 years in age and growing on good soil have 

 288 stems per acre, the mean girth of which at breast-height is 

 39 inches, but this is only attained or exceeded by about 40 % 

 or 115 stems; the mean average stems have also been found 

 to have a form-factor of 0-48, which is undoubtedly lower than 

 that of stems treated by the method of partial clearance. 

 Again, according to Lorey, the Silver Fir, when grown in pure 

 forest on good soil, yields 200 stems per acre with a mean 

 girth of about 52 inches at breast-height, which also is only 

 attained by about 40 % or eighty stems per acre. 



As has already above been pointed out, this method of 

 partial clearance with the distinct object of stimulating the 

 remaining crop to the speedy development of the larger and 

 more valuable assortments of timber cannot be successfully 

 attempted with regard to any species of tree when once its 

 natural energy of growth has practically abated to any con- 

 siderable extent, or on the poorer classes of soil ; but wherever 

 the trees are still capable of stimulation in respect to incre- 

 ment, and the productive capacity of the soil can be easily 

 safeguarded against deterioration, the method has decided 

 practical advantages which should strongly recommend them- 

 selves to the woodland proprietors of Britain, where sylvi- 

 cultural operations on any extensive scale should only be 

 conducted on strictly financial principles. 



