CHAP, x.] Stimulation of Increment 225 



it can be begun, the thinnings should, if possible, be com- 

 menced about the fortieth to sixtieth year. They should at first 

 be confined to the young stems of backward growth, and to 

 such as are never likely to attain good marketable shape. The 

 oftener the thinnings can be repeated at short intervals the 

 better, as any sudden exposure of the boles should be carefully 

 avoided. 



About ten or fifteen years after these preliminary operations 

 have been begun, the main partial clearance will in most cases 

 seem advisable ; for by that time the crop should be in a state 

 of active increment, due to the favourable influences of the 

 undergrowth and the previous thinnings. Here, again, as also 

 whenever further partial clearances are considered necessary 

 later on, the fall is in the first instance confined to trees that 

 have been damaged by organic or inorganic agencies, or that 

 do not continue to yield satisfactory increment ; and not until 

 all such unremunerative material has been removed should 

 any sound trees in energetic growth be cut out. 



When the main partial clearance has taken place about the 

 seventieth year, and has been followed by minor gradual 

 clearances at intervals of five years at first, then of ten, and 

 later on of fifteen, the preliminary yield or intermediate returns 

 thus obtained should amount, according to Kraft *, respectively 

 to about 288 to 628 cubic feet, then to 720 to 1,080 cubic feet, 

 and ultimately to 1,800 cubic ft. per acre, inclusive of branch- 

 wood. Past experience seems, according to Gayer 2 , to justify 

 the hope that by this method of treatment the same dimen- 

 sions of bole can be attained in about 120 years as are 

 obtainable in pure forests worked with a rotation of 200 to 

 240 years, provided that up till about the hundredth year the 

 rate of increment has been maintained at 3 to 3! %, and after 

 that at 2 to 2\ %, conditions which are quite conformable with 

 the actual results obtained on suitable soils. The crop of Oak 



1 Aus dem Walde, vol ix., p. 80. 

 3 Op. cit., p. 574. 



Q 



