IMPROVEMENT OF THE FOREST 209 



The cleanings are begun before the canopy is closed. 

 From that point until it is from 30 to 40 years old, the 

 stand is kept as dense as possible. During this period 

 the death of the lower branches takes place over a satisfac- 

 tory proportion of the stem. Then regular thinnings 

 begin. The first thinning removes the dead and the 

 suppressed trees. About 5 years later a second thinning 

 removes suppressed trees, and also cuts into the lower 

 intermediate class. Some 5 five years later a third thin- 

 ning is made, comprising, in addition to the above, many 

 of the intermediate and some of the co-dominant trees. 

 This brings the stand up to about the 50th year. The 

 main object up to this point has been the development 

 of form and quality. After this period the stand is 

 thinned much more heavily for the production of vol- 

 ume. The design is then to give the crowns the advan- 

 tage of full light. These cuttings occur every 5 years 

 till the stand is about 80 years old. During this period 

 the distance between the crowns is kept at about a meter. 

 After the 80th year the cuttings are made every 10 years, 

 and the crown distance is increased to about 2 meters. 

 Dr. Mayr classifies these last cuttings from SO years 

 on as accretion cuttings, and assigns the term "thin- 

 nings" to those from the cleanings to the 50th year. 

 The planting of an under-story, preferably of beech, as a 

 ground cover during the period of accretion cuttings is 

 recommended. 



Dr. Mayr estimates that ordinarily there would be 

 approximately 400 trees per hectar, or 160 per acre, at 



