DIAMETER LIMIT BY SINGLE TREES 233 



areas each year. This is simple and works well, because regeneration 

 immediately after clear cutting is practically certain. 



(c) Intermediate fellings. — These are regulated by cleaning, freeing, 

 or thinning an equal area each year. It was found that where the 

 volume to be removed by intermediate fellings, especially thinnings, 

 was limited the forest suffered silviculturally, consequently no limitation 

 of volume is considered advisable. 



(d) Selection high forests, usually maintained in the high mountains 

 solely for protection purposes, are, however, cut over periodically on a 

 cutting cycle of 12 to 20 years so as to remove the dead and dying trees 

 which would otherwise be lost. With a protection working group of 

 120 years and a 12-year cutting cycle 10 acres would be cut over each 

 year. At high altitudes where logging is difficult and expensive it is 

 often considered more practicable to combine several years' operations, 

 so under the conditions enumerated it would probably be better to cut 

 30 to 50 acres every 3 to 5 years rather than to log 10 acres, for the few 

 trees it would yield, each year. There is no Hmitation of volume since 

 the restriction of cut is secured by the silvicultural rule of cutting only 

 dead, dying, and deteriorating trees. 



Diameter Limit by Single Trees. — The basis for this method is to cut 

 all trees which have attained a certain diameter. This system, now 

 largely abandoned, was first used in the Vosges in the middle ages where 

 there was an excess of raw material and where only trees of a certain size 

 and number were wanted at the local sawmills. 



(e) Coppice (selection). — The selection coppice forests of beech are 

 found chiefly in the Pyrenees. When applied to high forest virgin stands 

 where age class normality is rarely found, there would be grave danger 

 of overcutting, for as Huffel says, ''Such a system can evidently only 

 be applied to forests very nearly normal." No illustration of the method 

 is necessary. 



(/) Cork bark. — The cork-oak bark yield ^^ is regulated by computing 

 the number of trees which bear bark thick enough to be merchantable. 

 In other words, there is the diameter limit idea applied to single trees 

 but it is gauged by the thickness of the bark (not by the total diameter 

 of the tree), and by the area to be harvested. (See also page 396.) 



Illustration. — The forest of I'Esterel is divided into two divisions 

 each with three working groups. It takes 12 years for the cork to reach 

 a thickness of 0.9 inch, the merchantable size, and it is collected on 

 a cutting cycle of 2 years. The yield is obtained by dividing the number 

 of trees (with salable bark on a working group) by 2 and multiplying by 

 the average yield per tree. 



^ For further details see Chapter III, French Forests and Forestry, by T. S. Woolsey, 

 Jr. ■ John Wiley & Sons, Inc., 1917. 



