Measures and yields of products and residues 3261 



Board feet per acre. — Yields of naturally occurring, mixed hardwood stands 

 are given in table 27-44. This table and the regression equations on which it is 

 based were developed with data from 641 plots in nine forest site types extending 

 from Virginia to Florida and west to Louisiana and Arkansas (Smith et al. 1975). 

 The authors note that the average yields from these sample plots are representa- 

 tive only of fully stocked, relatively uniform, even-aged southern hardwood 

 stands and are higher than can be expected from stands of inferior structure. 

 Only values for those forest site types where pines could likely predominate are 

 reproduced here. Smith et al. found that on upland slopes and ridge sites, total 

 green above-ground biomass, excluding only smaller pieces (less than 4 inches 

 dob) from tops and branches of larger trees, was 44 tons per acre in 20-year-old 

 stands and 162 tons per acre in 60-year-old stands (see col. 13 plus col. 17 of 

 table 27-44). Other sites had significantly more biomass per acre. 



Based on rangewide studies, Schnur (1937) prepared yield tables for fully 

 stocked, even-aged, second-growth upland oak forests (table 27-45). 



Yields for natural, unthinned stands of yellow-poplar (table 27-46) were 

 based on 141 plots in the Appalachian Mountains of North Carolina, Virginia, 

 and Georgia (Beck and Della-Bianca 1970). These even-aged stands each had 75 

 percent or more of the overstory in yellow-poplar. For each age on a given site 

 index, board-foot yield reaches a maximum volume, beyond which increases in 

 numbers of trees do not increase yield. Figure 27-3 illustrates this culmination at 

 four ages on site index 100, where a 60-year-old stand with 200 trees/acre 

 contains 600 bd ft/acre less than one with 150 trees/acre. Values in table 27-46 

 are in board feet International !/4-inch scale. Table 27-47 gives Scribner values 

 for yellow-poplar derived from 89 plots scattered well over the species range and 

 representing the best stocked areas that could be found (McCarthy 1933). 



Ash yields (table 27-48) are for pure, even-aged, well stocked stands on 

 different quality sites. 



Yield tables for a variety of hardwoods and from many different publications 

 are collected in Evans et al. (1975). 



THE CUBIC FOOT 



While the cord and board foot (log scale) are convenient units of volume, they 

 are indirect and only approximate measures of actual cubic volume. Cubic 

 measurement has a definite advantage: it accounts for the total wood content in a 

 tree without being tied to any particular end product. 



A cunit, the unit of measure used by the U.S. Forest Service for pulpwood or 

 sawtimber sales, is 100 cubic feet of wood fiber, always in the form of round- 

 wood — pulpsticks, sawlogs, or standing trees (Anonymous 1976). 



Cubic feet in logs. — The increasing value of logs and of products from whole 

 logs or residues has caused a trend in log scaling away from board-foot log rules 

 and towards cubic log rules. In fact, cubic log rules are now virtually standard 

 outside the United States (Hartman et al. 1978). 



Many cubic foot scales are based on formulae that mathematically transform 

 logs and bolts into equivalent true cylinders. Volumes, therefore, are computed 



