AMERICAN SYLVICULTURE 



III. European opinions continue to differ widely with reference 

 to the proper severitj- of thinnings. 



After Martin, the thinnings must leave the sectional area of 

 the forest constant by withdrawing, from a given age on, periodi- 

 cally the surplus of sectional area formed by growth. 



After Schwappach and Wimmenauer, the normal yield of .thin- 

 nings, expressed in per cent, of the final yield obtainable under a 

 rotation of IDO years, should be for Beech and for Scotch Pine 

 respectively : 



Beech after Scotch Pine after 



Soil. Schwappach. Wimmenauer. 



Best U7% 181% 



Medium 137% 145% 



Poor 124% 115% 



After Fricke, the relative length of the crowa and of the bole 

 free from green limbs is the best criterion of thinnings properly 

 made. At least 40 per cent, of the entire length of the tree should 

 be clad in green limbs. 



After Heck, no rule can be given the manner and the severity 

 of a thinning depending on local and even personal factors (" liberty 

 in thinnings"). Xo two trees being alike, a lack of a method is 

 better tlian a method of thinning. 



IV. Radically different from the systems of thinnings hereto- 

 fore prevailing are the revolutionary views proffered by Borggreve. 



Borggreve thinnings interfere or remove none but the pre- 

 domirators and dominators — the biggest poles — closest to the best 

 log size. Such thinnings begin but at the year sixty of a woodlotj 

 they withdraw every ten years one-seventh of the stems which, 

 being the largest, contain about one-quarter of the total volume. 



Of course, high and early revenue is secured by such practice. 

 On the other hand, the trees removed are those growing at the best 

 rate of interest. (From the sixtieth year on 90% of the annual 

 accretion in a woodlot is supplied by the 40% [in number] of the 

 largest trees). 



The advisability of a Borggreve thinning largely depends on 

 the reproductive power of a wood thus treated. In the case of 

 •Yellow Pine and on poor soil, the reproductive power of a wood 

 seems too small to allow of a speedy repletion of the growing stock 

 and of its leaf canopy. Much " food " goes to Avaste after Borg- 

 gi-eve thinnings. In the case of White Pine and Spruce, the danger 



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