24 IIKITISII FOREST TREES 



during thinnings out, c\:c. before the crops reach their normal 

 maturity. In regard to the proportion which under normal 

 circumstances the preliminary yield bears to the final 

 outturn Grebe l wrote as follows : 



" Granted that the thinnings begin at the proper time, in the case 

 of beech about 25 35 years, spruce about 20 30 years, and Scots 

 pine about 15 25 years, that they are regularly conducted, that the 

 yield therefrom is not reduced by any peculiar local circumstances (such 

 as right of collection of windfall, or interruption of density in canopy 

 due to snow accumulations, c. ), we may expect that on the average 

 the proportion which the intermediate yield from thinnings bears to the 

 final yield of the mature crop will be : 



/;/ Beech Forests 



With rotation of 80 years, from 12 20 per cent. 



ioo i4 2 5 

 ,, ,, 120 ,, ,, 16 30 ,, 



The lower percentage being on poor soils, the higher on the better 

 classes of soil. 



/;/ Spruce Forests 



With rotation of 60 years, from 15 17 per cent. 

 ,, ,, So ,, ,. 20 22 ,, 



100 ., ., 2326 



//; Scots Pine Forests 



With rotation of 60 years, from 18 24 per cent. 



So ,, 2228 ,, 

 ,, ,, 100 ,, ,, about 25 



In sprnce and pine woods the higher percentages are obtainable from 

 the inferior classes of soil. 



OENERAL COMPARATIVE CONSIDERATIONS REGARDING 

 TIMBER TREES. 



i. Requirements as to Climate exhibit themselves locally 

 in relation to atmospheric warmth, light, atmospheric 

 moisture, and currents of air. 



1 />if Bctriebf- itnd Ertragsrcgtbtng der Forstc. 2nd edition, 1879, 

 pp. 300, 301. 



