FOREST 



RESOURCES 



O F 



SOUTHEASTERN 



TEXAS 



Forest Increment Versus Drain 



■m- 



-*& 



Increment per acre 



THE increment or the volume growth of a 

 forest stand is the balance between growth 

 and the combined effect of death and decay. 

 Individual trees will increase their net sound volume 

 only when their growth exceeds loss that may 

 occur through decay. Likewise stands of timber 

 increase in volume only when the net growth of 

 the individual trees plus the volume added by 

 trees that move up into the stand from the seed- 

 ling sizes exceeds the loss of volume in trees that 

 die or decay during the period. Table 11 shows 

 the net growth rates of pines and hardwoods in 

 the various forest conditions during 1935, assum- 

 ing no cutting during the year. In the under- 

 sawlog sizes the conspicuously high rates are due 

 to the large volume of trees recruited into the 

 stand during the year from trees that were too 

 small to include in the inventory at the beginning 

 of the year. In sawlog-size conditions the propor- 

 tion of recruited volume from the small trees in 

 the stand is less, contributing to a lower rate of 

 increment. 



Table 1 1 . — Percent of annual increase of stands in the various 

 forest conditions, 7935 



Forest condition 



Pine 



Hardwood 



Board feet 



Cubic feet 



Board feet Cubic feet 



Old growth: 



Uncut.. - .- 

 Partly cut,. 



Percent 

 2.2 

 4.0 



8.4 

 8.8 

 38.3 



7.7 



Percent 

 2.5 



4.7 



6.5 

 6.3 



18.1 



5.1 



Percent 

 2.5 

 3.0 



4.3 

 5.2 

 13.5 



9.7 



Percent 

 2.2 

 2.4 



Second growth: 

 Sawlog size: 



Uncut -- 



3.8 

 3. 7 



Under sawlog size 

 Reproduction, clear-cut, and 

 fire-killed . 



7.0 

 3.5 



Weighted average 



8.3 



6.9 



3.8 



3.5 



The results of multiplying the average volumes 

 per acre by the percents given above are shown in 

 table 12, in which the increment per acre is ex- 

 pressed in board feet (International %-inch rule), 

 cubic feet inside bark, and cords. The pine and 

 hardwood components should be added for the 

 total growth per acre. 



Table 12. — Increment on the average acre in the various forest 

 conditions, 7935 ' 



Forest condition 



Pine component 



Hardwood component 



Old growth: 



Board 

 feet 

 72 

 66 



262 

 159 



88 



5 



Cubic 

 feet 

 16 



17 



55 

 35 

 27 



1 



Cords 



0.21 



22 



.72 

 .47 

 .36 



.02 



Board 

 feet 

 104 

 76 



43 

 44 

 14 



1 



Cubic 

 feet 

 22 

 15 



14 

 11 

 8 



Cords 

 0232 



Partly cut 



.23 



Second growth: 

 Sawlog size: 



.21 



Partly cut .. 



Under sawlog size 



Reproduction, clear-cut, 



.17 

 .12 









Weighted average... 



155 



35 



.46 



40 



12 



.18 



1 Cubic-foot increment is measured inside bark. 



Annual Volume Increment 



In applying the increment rates shown in table 

 12 to the growing stock in order to find the volume 

 increment for the year, suitable deductions were 

 made for the growth on trees that were removed 

 from the stands in the course of logging and other 

 utilization operations. The increases shown in 

 table 13, therefore, represent an estimate of the 

 actual amount of wood added to the volume of the 

 inventory during 1935, before utilization drain 

 was deducted. The increment expressed in board 

 feet in both pine and hardwood is the increase in 

 volume of saw-timber material only. The incre- 



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