YIELD TABLES BASED ON AGE, TO CUT-OVER AREAS 441 



so as to make this possible. The increment on this area for any con- 

 siderable period into the future depends on securing reproduction 

 to fill the gaps. 



The method of measuring increment on cut-over lands solely by the 

 growth expected on the trees left after cutting is best adapted to typical 

 many-aged or "selection" 1 forests, and the more closely the conditions 

 both as to distribution of cutting and of the residual stand resemble 

 a many-aged forest, the better the results obtained. This method 

 gives best results also on areas under intensive management, where if 

 trees die or are blown over, their volume is not lost, and when the danger 

 of reduction or loss in numbers is at a minimum. 



The necessity for reducing the number of trees for loss during the 

 period remains, and applies to all stands on cut-over lands as well as 

 elsewhere. Neglect of this factor means over-estimation of probable 

 net growth. 



339. Application of Yield Tables Based on Age, to Cut-over Areas. 

 Where stands in the original forest can be or have been separated 

 by area and age by any method, and a yield table based on age exists, 

 a more conservative method of calculating growth on cut-over lands 

 can be used, which bases this growth not on the theory of the many- 

 aged forest and crown expansion of the age class, but on that of even- 

 aged stands (§ 298). If age classes are on separate areas and cut clean, 

 the cutting of one stand has no effect on the growth of another. If 

 the forest is divided into age classes, and part is cut over, it can be 

 assumed that this cutting removes an age class without stimulating 

 the growth on the remainder, and that this area cut over is to be repro- 

 duced to young timber rather than absorbed by existing age classes. 



To determine the area which is cut over, and that which remains 

 stocked, the density or reduction per cent already determined for the 

 original forest (§ 317) is assumed to apply to the residual stand. The 

 area stocked to this degree of density can be found by dividing the 

 volume in each age class left on the cut-over area, by that of the empirical 

 yield table for the given age which has been prepared for the original 

 forest previous to cutting (§ 304). The sum of these areas, including 

 that stocked already by young or immature age classes, subtracted 

 from the total area, gives the area actually cut over. The actual yields 

 of the age classes left on the cutover area will be in proportion to the 

 per cent of the total area which they occupy, plus the degree of expansion 

 or increased growth which they put on. The growth to be expected 

 in the absence of any such expansion will be predicted by the empirical 

 yield table from the net area or per cent of area stocked. This fixes 



1 Selection — A term applied to forests in which the entire series of age classes is 

 intermingled over the whole area and not separated by areas. 



