1904 



FORESTRY AND IRRIGATION 



269 



that the cover is permanently broken. 

 As a result, builders always specify 

 foreign-grown timber in their plans for 

 all but poorest grades, the home-grown 

 stock selling far below the importe'd.* 



Aside from quality, there is also a 

 much greater volume yield per acre by 

 close planting. In a natural forest the 

 yield over a large area seldom exceeds 

 25,000 feet, yet in Germany for the 

 whole coniferous forest the average 

 stand of merchantable Scotch pine is 

 42,000 B. F, per acre and for spruce and 

 fir about 77,000 feet. 



To understand the conditions which 

 produce such yields from the small per 

 cent of planted trees, the life history of 

 the individuals in the stand must be 

 analyzed. Such a forest usually closes 

 about the sixth year, and from that time 

 on each tree enters into fierce combat 

 with its neighbors for light and room. 

 The struggle soon has its effect on the 

 individuals of the stand, which may then 

 be divided into three broad classes : 

 Dominant, overtopped, and suppressed. 

 Narrower classification separates the 

 dominant class into three, making the 

 division as follows : 



I. Decidedly dominant. Trees with 

 exceptionally well-developed crowns. 



II. Dominant. Trees with well-de- 

 veloped crowns. 



III. Codotninant. Trees with fairly 

 normal crowns, but with relatively poor 

 development. 



IV. Overtopped. 



a. With badly formed crown, but free 

 in one or more directions. 



b. Very poor crown, but still free in 

 one direction. 



V. Suppressed. 



a. Crown still thrifty, but absolutely 

 overtopped. 



b. Dying or dead. 



As the number per acre falls so sud- 

 denly with the development to maturity, 

 it stands to reason that the greatest num- 

 ber of trees and the main increment must 

 be found in the dominant stand. Ex- 

 periment has proved that the per cent of 

 total increment in the five classes com- 

 pared with their relative number per 

 given area is as follows : 



* Parliamentary Report on British Forestry, 

 1903. 



Spruce 18 to 30 Years 



As the total number of trees at this 

 age is about 1,650, it is evident that the 

 future merchantable yield will be made 

 up of only a small part of classes I and II , 

 and that the increment of the other trees 

 will be last in the depletion of the stand 

 as it matures. 



The main object of the thinning then 

 is two-fold: 



1 . To use the growth of the interme- 

 diate stand, which is not inconsiderable. 



2. To shift as much as possible of the 

 total increment on the trees of the final 

 stand by the removal of trees which 

 crowd it, but \vhich can not mature as 

 merchantable trees of desired quality. 

 The following table, the figures of 

 which are taken from various experi- 

 mental areas, adds clearness to the sub- 

 ject: 



Spruce, First Quality. 



From this it is clear that at maturity 

 200 trees or so can produce the same 

 volume of merchantable timber as 250 

 or even 300 trees, and that the difference 

 can be used in the interim without de- 

 creasing the final crop ; nor does this 

 take into consideration the improved 

 quality and greater value of timber in 

 the final stand. In the preceding table 

 it will be noticed that the best acres for 

 volume show the best development in 



