N 



Forest Increment and Drain 



■»» 



-<«- 



Net Increment 



A FOREST is a perpetually changing association of 

 trees in which growth tends to offset losses. While 

 natural growth is almost ceaselessly adding to the 

 volume ot timber, other factors — natural and man-caused — 

 are continually causing reductions. Net increment, or the 

 net gain from the action of natural factors alone, represents 

 in a general way the quantity of wood that could be cut 

 within the period covered by the calculations without re- 

 ducing the growing stock, or forest capital. This may in 

 some instances, of course, be nil or, it the mortality loss 

 exceeds growth gain, a minus increment. It is against this 

 net increment that the loss from timber cutting, or com- 

 modity drain, must be charged. 



The Forest Survey estimates that the gross increase in 

 the saw-timber volume of Louisiana forests during 1937 was 

 2.4[billion board feet; against this there was a mortality loss 

 of 0.5 billion board feet, leaving a net increment of 1.9 bil- 

 lion board feet (table 12). Although pines constitute onlv 

 about a third ot the total growing stock, they account for 

 more than halt the total net saw-timber increment. Their 



Table 12. — Net increment of pities ami har<i'j:ootis in Louisi- 

 ana, expressed in board feet, cords, and cubic feet ' 



SljrcifS 



Growth 



Mortality 



Inereinent 



Piius . 



11 anlwoods (cypress) 



Billion 

 board ffft 

 1.16 

 1.25 



Billion 

 board fed 

 0. M 

 35 



Billion 

 board feel 



1.02 

 .90 







.\11 si)ccies.. 



2.41 



.49 



1.92 



Tines 



Million cords 

 H. 7 

 5.5 



Million cordt 

 0.5 

 1.7 



Million cords 



Ilurd woods 



3.S 



All species. 



9.2 



2.2 



7.0 



rines 

 Hiirdwdods , 



Million cubic 

 fed 



279 

 385 



Million cubic 

 f"t 



41 

 114 



Million cubic 

 fett 



271 



All species 



WH 



l.W 



:*i9 



larger net increment is due primarily to their more rapid 

 rate of growth, and secondarily to their lower mortality 

 rate, which in 1937 was 0.93 percent as compared with 

 1.33 percent for hardwoods and cvpress. 



Old growth Second q-o^-M ;^ , 

 ' so«iog i :t 



FlGlnE 11.— Relation of foresl-iaHj etm 

 senc-timhrr incremtnt, f-\ •, r.-..-. ,., ,•■.,•>, 



to tatsl 



•1 (l4U], 



Dalii li> roKioiis ure Ki^eii in laMes .'I 2'., Ai'pcii.liv. 



During that year, it no cutting had taken place, the 

 saw-timber volume within the State wouUl have incix-ascvl 

 by 4.6 percent, or an average increment per acre for the 

 entire forest area of 119 Uiard feet. In 1934 and 1*^35 

 the second-growth sawlog-size stands, because of their 

 good stocking and general thrift, had an aver.igc'" 



31 



