2JO 



FORESTRY AND IRRIGATION 



June 



height. Any curve of height growth 

 shows a decided falling off after the 

 fortieth year or so, and a method that 

 will stimulate growth during this period 

 is likely to add directly to the yield. 

 This seems to be the case in these in- 

 stances and adds evidence to the value 

 of thinnings. 



To recapitulate, the importance of 

 thinnings lie in the improved quality 

 and quantity of the final yield obtained 

 by the use of timber, which would other- 

 wise go to waste, thus giving an inter- 

 mediate yield which greatly helps the 

 financial success of the long crop rota- 

 tion often necessary in forestry. This 

 intermediate yield is an appreciable item 

 in every German forest estate. The av- 

 erage annual intermediate yield of mer- 

 chantable poles and logs for Wiirtetn- 

 berg amounts to 252 cubic feet, for the 

 first-quality class of conifers it is 378 

 cubic feet, and in special cases it often 

 comes to 840 cubic feet. Other good 

 results of thinning are as follows : 



1 . The mixture can be regulated and 

 undesirable species removed. 



2. The quality of the mixture bet- 

 tered decayed, diseased, and badly 

 formed trees removed. 



3. The danger of breakage from snow, 

 ice, and storm lessened. By allowing 

 each crown and bole a better develop- 

 ment, the cover is made stronger and 

 more resistant to storms. 



4. The danger from insects and fire 

 is lessened by the removal of dead and 

 dying timber. 



B. The Technique of Thinning. 



All systems of thinning are based on 

 a division of the stand into classes sim- 

 ilar to those given above. Until quite 

 recently only three degrees were in com- 

 mon use, being designated by the let- 

 ters A, B, and C, or "light"" "me- 

 dium," and " heavy," the C, or heavy, 

 not breaking the forest cover by more 

 than 2.5 per cent. These grades cut 

 into the stand as follows : 



Of late less conservative ideas have 

 come into vogue, and in all recent ex- 

 periments the division is made into four 

 main grades: A, light; B, medium; C, 

 heavy, and D, very heavy. The classes 

 taken under this system and the per 

 cent of the total stand removed are as 

 follows : 



Thinning. 



A.. 

 B.. 

 C. 



Classes removed. 



V, b and a. 



V, b and a, and IV, b. 



V, b and a, and IV, b and a. 



A stand of maturing trees falls into 

 two main classes in reference to the fu- 

 ture merchantable crop: Th&jinal stand, 

 out of which the mature trees will be 

 recruited, and the intermediate stand, 

 which has fallen behind and will evi- 

 dently perish before the period of rota- 

 tion is over. These two divisions vary 

 in composition \vith the age of the forest. 

 In relation to each other, however, they 

 are constant, the final stand being com- 

 posed of classes I, II, and III, and the 

 intermediate stand of IV and V. The 

 less radical methods of thinning only 

 attack the intermediate stand, but C 

 and D enter boldly into the recruiting 

 ground of the final crop. Common ex- 

 perience in practice, without experi- 

 ment, has shown that slight thinning 

 neither gives a very paying interme- 

 diate yield, nor greatly improves the 

 growth and quality on the final stand. 

 The value of this method seems clear 

 from the figures given above, which 

 show that the greatest increment and 

 the greatest number of trees are in 

 classes I and II ; hence it follows that 

 competition is most severe in this class, 

 and that the greatest volume can be 

 most profitably removed therefrom. 



Beside grades C and D many systems 

 of regular thinning in the final stand 

 have been advocated, the most practi- 

 cal and generally used of which is the 

 French method, edaircic par le haut. 

 By this the best trees of the final stand 

 (approximately equal to the number of 



