Cubic-Foot Increment 



The cubic foot is a unit of measurement appli- 

 cable to all the material in the forest. The aggre- 

 gate net cubic-volume increment (excluding bark) 

 for 1934 is approximately 71 million cubic feet, 



made up as follows: 



AHlUon 



cubic Jeet 



(ivithout 



bark) 



Stem wood of good trees (both sawlog size and under 



sawlog size) 44. 83 



Top wood of good trees of sawlog size (including 



limbs) 18.89 



Stems and tops of sound cull trees 6. 36 



Sound portion of stems and tops of rotten cull trees . . 1.12 



Total 71.20 



Considering the forest as a whole, the average 

 net annual increment per acre in stem wood of 

 good trees is 17.1 cubic feet. This average incre- 

 ment varies on commercial areas between approxi- 

 mately 6 cubic feet per acre in the old-growth, 

 partly cut condition and 39 cubic feet in the second- 

 growth, sawlog-size condition. On the noncom- 

 mercial areas the cubic-foot increments are some- 

 what greater in the old-growth condition and 

 somewhat less in the second-growth condition. 



Again considering the forest as a whole, the aver- 

 age net cubic-foot increment per acre of sound 

 material in stem wood, top wood, and sound and 

 rotten cull trees is approximately 27 cubic feet. 

 This average growth per acre is low because of (1) 

 large areas of slow-growing, overmature, old- 

 growth timber; (2) prevalence of understocked 

 stands; (3) an unusually large proportion of slow- 

 growing species such as overcup oak, bitter pecan, 

 cedar elm, and hackberry; and (4) a large number 

 of relatively nonproductive sound and rotten cull 

 trees. Under even a very simple system of forest 

 management these conditions could be improved 

 and the average cubic-foot increment increased. 



Diameter Growth 



The current rate of diameter increase was 

 measured on approximately 4,000 trees of all 

 species uniformly scattered throughout the unit. 

 Table 12 gives the average 10-year increase in 



diameter for important species groups and diam- 

 eter-class groups, with a summary by different 

 forest conditions. Although the average 10-year 

 diameter increase for all species and conditions is 

 in the neighborhood of 2 inches, individual species 

 vary considerably from this average. Cottonwood, 

 willow, red oaks, and Avater oaks giow conspicu- 

 ously faster than the average; while overcup oak, 

 elms (due chiefly to the large proportion of cedar 

 elm), black gum, bitter pecan, hickory, and hack- 

 berry are notably slo\v growers. 



Table 12 furnishes a basis for an approximate 

 estimation of the diameter growth to be expected 

 in any southern bottom-land hardwood forest, the 

 composition of which is known by conditions, 

 species, and sizes. 



Table 12. — Average diameter growth in W years of the various 

 species groups and diameter-class groups 



Species group and forest enndif ion 



Red gum 



Water oaks 



Red oaks 



White oaks 



Overcup oak 



Ash 



C otton wood 



Willow 



Elms ._ 



Tupelo gum. 



Black gum 



C y press 



Bitter pecan _ ___ 



Hickory 



Sweet pecan 



Hackberry 



Pine 



Persimmon 



Red maple and boxelder 



Other hardwoods 



Weighted average 



Summary by forest conditions 



Old growth, uncut 



Old growth, partly cut 



Second growth: 

 Sawlog size: 



Uncut 



Partly cut 



Under sawlog size 



Weighted average 



Growth in diameter-class 

 group of— 



6-12 

 inches 



Inches 



1.90 



1.49 

 1.68 



1.89 

 1.77 

 2.55 



1.90 



14-18 20-28 

 inches inches 



Inches 

 2.18 

 3.14 

 3.05 

 1.92 

 1.71 

 2.03 

 3.29 

 4.18 

 1.59 

 2.62 

 1.80 

 2.01 

 1.46 

 1.33 

 2.73 

 1.55 

 2.80 

 1.23 

 3.12 

 2.23 



Inches 

 2.02 

 2,80 

 3.93 

 1.79 

 1.37 

 1. 55 

 3.59 

 3.65 

 1.62 

 2.42 

 1.57 

 2.23 

 1.53 

 1.50 

 2.08 

 1.47 

 3.00 

 2.23 

 2.32 

 2 00 



2.15 



2.04 



1.45 

 1.75 



2.04 

 2.79 

 2.37 



1.42 

 1.91 



3.00 

 2.58 

 2.22 



2.15 



2.04 



30+ 

 inches 



Indies 

 1.49 

 2.09 

 1.70 

 1.80 

 1.35 

 1.16 

 3.18 

 2.85 

 2.21 



1.98 

 .90 

 1.70 



2. 25 



3.20 

 2.37 



1. 64 

 1.86 



2.35 

 2,80 

 1.S4 



1. 



26 



