i88 



Studies in Forestry 



[CHAP. IX. 



In mixed forests the practice of thinning must, of course, 

 be conducted on quite a different principle from that obtaining 

 with regard to pure woods. Thus in order to save a valuable 

 species of tree, it may very often be found necessary to cut out 

 other kinds of more energetic growth, which may threaten to 

 prejudice its development, or even to endanger its existence. 



As regards the influence which the species of tree has on the 

 extent to which thinnings are necessary, Schuberg 3 found in 

 the Black Forest that in forty to eighty-year-old crops, which 

 had been regularly thinned, the following were the results on 

 soils of average quality : 



If the chief light-demanding genera (Pine, Larch, Oak, Ash, 

 Maple, Birch, &c.) be grouped together, and be compared with 

 the various shade-bearing kinds of trees, it will be found that 

 on the whole these, latter only require on the average from 

 50 to 75 %, or one-half to three-quarters, of the growing-space 

 demanded by the former for their proper development as 

 a woodland crop. 



The quality of the soil is also a very important factor in deter- 

 mining the number of stems per acre. Owing to the more 



1 Gayer, op. tit., p. 550. 



