98 



method consists in the gradual removal, by successive fellings 

 over definite and limited areas, of the crop to be regenerated. 

 While this regeneration by successive fellings is proceeding, 

 the crops "which have been or have still to be regenerated 

 are subjected to cleanings and thinnings. The principal or 

 regeneration fellings are prescribed by volume, that is to 

 say, the possibility in cubic feet having been ascertained, as 

 many trees as are found to yield this volume are removed 

 wherever, in view of the state of the crop, this is reqviired 

 for sylvicultural reasons. 



Possibility : volumetric method.— Formerly the volume of 

 material to be removed annually was determined by the 

 volumetric method, which consists in calculating the total 

 volume of wood produced in an interval of time equal to 

 the exploitable age, and by dividing this total by the number 

 of years in that age. The method is still sometimes em- 

 ployed. 



The manner in which the calcniation is eCfected may best he explained by an 

 example. Supjiose a forest of 1,600 acres, which it is wished to exploit at 120 years, 

 divided into compartments or cultural subdirisiuns each containing a crop of an uni- 

 foriri asre. The exploitable age would be divided into, say, four periods of 30 years 

 each, and the area, provisionally, into four con-esponding blocks, the first con- 

 taining the crops above 90 years' old, the second those of 60 to 90 years, the third 

 those of 30 to BO years, and the fourth those below 30 years. 

 Thus:— 



1st Block. 



years old. 



And so on for the other bloclcs. This preparatory olaRsification having been effected, 

 the volume of material in each compartment is calculated, and to this volume is 

 added the estimated future increment tip to the time when the compartment will be 

 regenerated, that is to say, 15 years' growth (the mean of the 30 years during which 

 ail the compartments would be regeneiated, some at the b-ginning, some at the 

 end ot the period) for the compartments forming the first block, 45 years' growth 

 for the compartments forming tlie second block, 75 for those forming the third 

 block, and 105 for those in the fourth block, thus : — 



1st block, aetoal volume 13,86,ono c. ft. estimated growth 16 jeare, 210.000 eft. total l,69e.C00 c,ft. 



;"f •• ■■ 393.000 ,. „ 45 „ 721^000 „ „ 1 113.000 „ 



5J? '. .. 435,000 ,. „ 75 ., 1,246,000 ., „ l,680,(i00 „ 



"" >• .. 262,000 ., „ 105 „ 1,419,000 „ „ 1.681,000,, 



Total . 6.070,000 o.tt. 



Consequently, the total volume to be felled during the first period of 30 years, after 

 ■whic?! the calculations would be revised, is 6,070,000-4-4 = 1,517,500 cubic feet, and 

 each year l,517,50O-f-3O=5O,583 cubic feet. The permanent plan would then be drawn 

 up by allotting to the first block, to be regenerated during the period of 30 years, a 

 Bufiicient number of the compartments containing the oldest crops to furnish, includ. 

 ing I nture increment, 1,517,500 cubic feet of material. As the compartments tempo- 

 rarUy included in the first block will furnish 1,596,000 cubic feet, certain crops 

 shonW now be allotted to the second block instead. There would then be felled each 



