Expected Volume and Value of Structural Dimension Lumber from

25-, 30-, 35-, 40-, and 50-Year Old Loblolly Pine Plantation Timber

 

 

Dr. Evangelos J. Biblis, Professor Emeritus & Dr. Honorio F. Carino, Professor

 

School of Forestry & Wildlife Sciences

Auburn University, AL 36849, U.S.A.

Tel. - (334) 844-1090,             Fax - (334) 844-4221

E-Mail – biblisej@auburn.edu, or carinhf@auburn.edu

  

           

Abstract

            The expected volume and value (based on Summer 2000 prices) of structural dimension lumber derived from plantation-grown timber of 25-, 30-, 35-, 40-, and 50-year old loblolly pine (Pinus taeda L.) were estimated and used to determine stumpage values through regression analysis. Also, incremental analysis in conjunction with discounted-cash-flow techniques were used to determine the economic desirability of deferring the harvesting of a loblolly pine plantation stand of a given age for purposes of producing structural dimension lumber.

            The results of the study provide compelling evidence that indeed the volume and quality of sawlogs from loblolly pine plantations generally increase with stand age. It was found, for instance, that for 25-, 30-, 35-, 40-, and 50-year old loblolly pine stands like those investigated, the expected total volume yield of stress-graded dimension lumber could be as much as 94.4 m3/ha. (16.2 mbf/acre), 122.4 m3/ha. (21.0 mbf/acre), 151.0 m3/ha. (25.9 mbf/acre), 179.0 m3/ha. (30.7 mbf/acre), and 235.0 m3/ha. ( 40.3 mbf/acre), respectively.  On average, the expected annual increase in volume yield could be about 5.61 cu.m./ha. (0.96 mbf/acre).  The increased quality of older loblolly pine plantation timber was clearly reflected by the percentages (based on volume yield) of stress-graded dimension lumber graded No. 1 & Better, which were 16.0%, 36.2%, 46.7%, 49.3%, and 83.0%, respectively, for 25-, 30-, 35-, 40-, and 50-year old stands. This was also reflected by the expected unit value yield which were $106/m3 ($250/mbf), $123/m3 ($290/mbf), $140/m3 ($330/mbf), $157/m3 ($370/mbf), and $192/m3 ($450/mbf), respectively.  On average, the expected annual increase in unit value yield could be about $3.42/m3 ($8/mbf).

 

            Not surprisingly, the stumpage value of loblolly pine plantations based solely on the value of structural dimension lumber produced also increases with stand age.  For 25-, 30-, 35-, 40-, and 50-year old stands like those investigated, the expected total value yield of stress-graded dimension lumber could be as much as $10,006/ha. ($4,055/acre), $15,055/ha. ($6,100/acre), $21,140/ha. ($8,531/acre), $28,103/ha. ($11,346/acre), and $45,120/ha. ($18,133/acre), respectively.  On average, the expected annual increase in value yield could be about $1,399/ha. ($566/acre).

            Also, it was determined that it would be economically desirable to defer the harvesting of a 25-year old plantation stand of loblolly pine like the one investigated by 5, 10, 15, or 25 years if the minimum acceptable rate of return on investment (MARR) is less than 8.5%, 7.7%, 7.1%, or 6.2%, respectively.  For a 30-year old stand, it would be economically desirable to defer  harvesting it by 5, 10, or 20 years if the MARR is less than 6.9%, 6.4%, or 5.6%, respectively.  For a 35-year old stand, it would be economically desirable to defer harvesting it by 5 or 10 years if the MARR is less than 5.9% or 4.8%, respectively.  For a 40-year old stand, it would be economically desirable to defer harvesting it by 10 years if the MARR is less than 4.8%.

INTRODUCTION

            Loblolly pine (Pinus taeda L.) is the most important species of timber growing in the southern region of the United States of America.  It is considered an ideal tree for site restoration and forest management, largely because of its hardiness and versatility in terms of its ability to reproduce and grow rapidly on diverse sites (Schultz, 1997).  More than half of the southern yellow pine timber now available to sawmillers in the region comes from plantations consisting mostly of loblolly pines.  However,  dimension lumber producers are noticeably avoiding whenever possible the use of timber from intensely managed loblolly pine plantations apparently because of the fact that fast-grown pine trees produce a high proportion of juvenile wood at young ages.  Juvenile wood, which in loblolly pine could occupy from 10 to 20 annual rings (Zobel and Kirk, 1972), is generally undesirable for solid wood products production.  It is known to be weaker and less stiff than mature wood due to its lower specific gravity, shorter tracheids, larger fibril angles, thinner cell walls, larger lumen diameter, lower percentage of summerwood, more compression wood, and larger longitudinal shrinkage (Pearson and Gilmore, 1971; Zobel and Kirk, 1972; Zobel and Blair, 1976).

            It has been determined that the structural quality of dimension lumber from loblolly pine plantation sawtimber increases with stand age and stand density (Biblis et al., 1993; Biblis et al., 1995; Biblis et al., 1997; Biblis and Carino, 1999).  This confirms the widespread belief among


wood industry people that quality, and not just volume, of loblolly pine plantation timber increases with stand age.  Therefore, the stumpage value also increases with stand age, and a stratified stumpage pricing reflecting the quality differences of sawlogs or sawtimber from loblolly plantation stands of different age groups should be considered.

            Also, a recently conducted study (Biblis et al., 1998) presents compelling evidence that sawtimber regimes of loblolly pine plantations with longer rotations (e.g., 50-year) could provide competitive returns to landowners relative to pulpwood regimes with shorter rotations (e.g., 20-year).  The expected economic advantage might even be greater if loblolly pine plantation stands were managed to produce sawtimber purposely for structural dimension lumber production, as shown in this paper.  For instance, it was estimated based on Summer 2000 prices that a 25-year-old loblolly pine plantation on an average site (e.g., 90/50 site index, i.e., tree height of 90 feet (or 27.4 meters) at 50 years old) and with a 8- by 8-foot (or 2.4- by 2.4-meter) initial spacing could yield about $4,055/acre (or $10,006/ha.) of stress-graded dimension lumber from the harvested sawtimber.  In contrast, the same stand if managed to produce pulpwood would yield only up to $1,000/acre (or $2,471/ha.), i.e., based on a rather optimistic timber harvest of 40 cords/acre (or 257 tons/ha.) at $25/cord (or $9.62/ton).

            There is no doubt that older stands of loblolly pine plantation timber yield higher expected income for the owners.  However, there is a dearth of information about the volume and value of structural dimension lumber yields from loblolly pine plantation timber of various ages.  More importantly, the economic harvest rotation of loblolly pine plantations for structural dimension lumber production is not known.  Not much is known, for instance, if it would be economically advantageous and desirable for a sawmiller/landowner to defer for another 5, 10, 15, or 25 years the harvesting of a 25-year old plantation stand of loblolly pine sawtimber for structural dimension lumber production.  This paper provides invaluable insights into this important issues.

METHODOLOGY

            Five loblolly pine plantation stands representing 25-, 30-, 35-, 40- and 50-year age classes, respectively, were used for this study.  These were selected primarily due to their very similar characteristics including site indices, original spacing and thinning regimes as listed in Table 1.  The diameter at breast height (dbh) distribution was established by measuring the dbh of all trees in four 1/4 acre (0.10 ha.) sample plots.  Fifty trees representing the predetermined dbh distribution in each of the 25-, 30-, and 35-year old stands were selected for sawing.  Also selected in a similar fashion were 30 trees from the 40-year old stand and 12 trees from the 50-year old stand.   All selected sample trees were identified, harvested, measured, and segregated prior to bucking them into sawlogs.  Each sawlog was measured, recorded, and spray painted on each end with different colors - one to indicate the stand age the other the log location within the tree.

            For each batch of sawlogs of a given type (i.e. based on stand age and tree section - butt, middle, or top), the sawn pieces of lumber were tallied and sorted by width and length.  About 5.46 mbf (12.9 m3), 4.67 mbf (11.0 m3), and 10.45 mbf (24.7 m3) of lumber were recovered from each group of 50 trees harvested and sawed representing the 25-, 30-, and 35-year old stands, respectively.  Moreover, 6.08 mbf (14.3 m3) and 4.03 mbf (9.5 m3) of lumber were recovered from the 30 and 12 trees harvested from the 40- and 50-year old stands, respectively.  The lumber was then kiln-dried to approximately 15% moisture content and subsequently dressed to the mill’s specifications for dimension lumber.

            The lumber produced from each plantation stand investigated were subsequently tested mechanically using the destructive method of determining flexural properties (moduli of rupture (MOR) and elasticity (MOE)).  For this purpose, 338, 374, and 474 lumber samples were randomly selected from the 25-, 30-, and 35-year old stands, respectively.  On the other hand, all the lumber pieces (468 and 356, respectively) produced from sawlogs originating from the sample trees (30 and 12 trees, respectively) representing the 40- and 50-year old stands were selected for testing.  These were stored indoors at the Auburn University Forest Products Laboratory for a minimum of three weeks prior to testing.  Every piece was tested edgewise in flexure to failure with two point loading according to ASTM D198-84 (American Society for Testing and Materials, 1999), using a Tinius-Olsen hydraulic testing machine with a capacity of 120,000 pounds (54,545 kg.).  It should be noted that only two length categories (i.e., 8- and 12-foot or 2.4- and 3.7- meter) of lumber were tested.  The 2- by 6-inch (5.08- by 15.24-cm.) and 2- by 8-inch (5.08- by 20.32-cm) pieces were tested over a span of 132 inches (3.35 m.), and the 2- by 4-inch (5.08- by 10.16-cm.) pieces were tested over a 90-inch (2.3-m.) span.  For flexure tests, the machine was equipped with an extended base made from a steel double I-beam 20.5 feet (6.25 m.) long and a steel loading head 7 feet (2.13 m.) long.  Load and corresponding deflection-to-failure data were obtained with a Hewlett-Packard (H-P) data acquisition system connected to an H-P desk computer for processing.  From the obtained data, the MOR and MOE for each tested piece of lumber were calculated. To obtain the extreme fiber value in bending "Fb" for every tested piece, its MOR value was divided by the 2.1 combine safety factor recommended in ASTM D245 (American Society for Testing and Materials, 1999).  This "Fb" value in


combination with the corresponding appropriate value "E" provides  the stress grade for each lumber size listed in Tables 1a, 1b, and 1c of the SPIB Standard Grading Rules (Southern Pine Inspection Bureau, 1994).

            The volume and value of the test sample boards for each combination of size and stress-grade classes originating from a stand of a given age were then determined. The valuation of lumber was based on lumber prices (in $/mbf or $/cu.m.) quoted directly from southern yellow pine lumber producers for the Summer months of 2000.  From the test sample data, it was then possible to estimate the probability of occurrence (or percent distribution) of stress-graded dimension lumber coming from each sample stand of a given age based on volume (see Table2).  Also, it was possible to estimate the weighted average unit value (in $/mbf or $/cu.m.) of the tested dimension lumber from each sample stand of a given age, using the following relationship:

                        Vk =  Pij Rij                                                                                        [1]

where:  Vk   =   weighted (by size and grade) average unit value ($/mbf or $/cu.m.) of tested (i.e., stress-graded) dimension lumber from a loblolly pine plantation of a given age k.

Pij  =  probability of occurrence of tested dimension lumber of a given size i and grade j from a loblolly pine plantation of a given age.

Rij   = unit price ($/mbf or $/cu.m) of tested dimension lumber of a given size i and grade j.

The estimated weighted average unit value (in $/mbf or $/cu.m.) of the tested dimension lumber from the 25-, 30-, 35-, 40, and 50-year old stands are $236/mbf ($100/ m3), $300/mbf ($127/ m3), $355/mbf ($150/m3), $352/mbf ($149/m3), and $452/mbf ($192/m3), respectively.

            The total volume of dimension lumber per acre of loblolly pine plantation of a given age was estimated using the data on the number of sample trees harvested for the study, the volume of dimension lumber produced from such sample trees, and number of trees at harvest time.  For instance, in the case of the 25-year old stand, the total volume of dimension lumber is about 16.8 mbf/acre (i.e., given the number of trees/acre at harvest time = 154; number of sample trees harvested = 50; volume yield of 50 trees = 5.45 mbf ) or 97.9 m3/ha.  Calculated in a similar fashion, the estimated total volume of dimension lumber from the 30-, 35-, 40-, and 50-year old stands are 16.2 mbf (94.4 m3/ha.), 27.2 mbf (158.6 m3/ha.), 36.9 mbf (215.1 m3/ha.), and 37.0 mbf (215.7 m3/ha.), respectively.

            Given the data on weighted average unit value (in $/mbf or $/cu.m.) and the estimated total volume of dimension lumber per acre, it was then possible to estimate the total value of dimension lumber per acre of loblolly pine plantation of a given age.  The estimated total value of dimension lumber of the 25-, 30-, 35-, 40-, and 50-year old stands are $3,969/acre ($9,808/ha.), $4,878/acre ($12,054/ha.), $9646/acre ($23,836/ha.), $12,988/acre ($32,094/ha.), and $16,712/acre ($41,296/ha.), respectively.

            For purposes of predicting expected values (see Table 3) as well as observing trends and rates of change of the unit value, total volume, and value of stress-graded dimension lumber produced per acre of loblolly pine plantation of various ages from 25 to 50 years old, the following regression equations were developed:

                                    Y1 = -7.86 + 0.96X,                r2 = 0.82                                              [2]

                                    [Y1 = -45.80 + 5.61X]

where:    Y1 =  expected total volume of stress-graded dimension lumber per unit area (mbf/acre or cu.m./ha.) of  loblolly pine plantation of a given age; equation in brackets for metric estimation.

                X = stand age (yrs.)

                                    Y2 = 5.00 + 8.00X,                 r2 = 0.94                                              [3]

                                    [Y2 = 20.59 + 3.42X]

where:    Y2 =  expected unit value ($/mbf or $/cu.m.) of stress-graded dimension lumber from a loblolly pine plantation of a given age; equation in brackets for metric estimation.

                X = stand age (yrs.)

            The expected value of stress-graded dimension lumber produced per acre of loblolly pine plantation of a given age was estimated by multiplying the values given by Equations 2 and 3.  In this study, a modified version of stumpage valuation was used in the analysis.  Stumpage was estimated by the value of structural dimension lumber yield based on actual volume recovery (instead of scaled volume as conventionally done in practice).  With such a modified valuation of stumpage notwithstanding, the economic desirability of deferring the harvesting sawtimber for structural dimension lumber production from a loblolly pine plantation of a given age was determined using incremental analysis in conjunction with discounted-cash-flow techniques.  For this analysis, the following relationship proved to be very useful:

                                    R  =  [(F/P)1/n - 1] x 100                                                                      [4]

            where:      R = expected incremental rate of return (%)

                             P = expected present value ($) of stress-graded dimension lumber produced per acre of loblolly pone plantation of a given age.

                            F  =  expected future value ($) of stress-graded dimension lumber produced

                                    per acre of loblolly pine plantation after n years from a base age.

                              n = stand age (yrs.)

A decision to harvest the stand at a certain age (e.g., 25 years old), and not later (e.g., after 5 years or 30 years of age), would be implemented if R is less than a specified minimum acceptable rate of return on investment (MARR).  Otherwise, it would be more economically desirable to defer the harvesting of the stand until more favorable economic conditions exist or whenever an R equal to or higher than the MARR could be achieved (see Table 4).

RESULTS AND DISCUSSION

            From Table 3, it is apparent that the value of stumpage in loblolly pine plantations increases with the age of the stand.  The estimated total value yield of stress-graded dimension lumber of the 25-, 30-, 35-, 40-, and 50-year old stands are $4,055/acre ($10,020/ha.), $6,100/acre ($15,073/ha.), $8,531/acre ($21,081/ha.), $11,346/acre ($28,037/ha.), and $18,133/acre ($44,808/ha.), respectively.  These represent an annual average increase of about $566/acre ($1,399/ha.), as determined by regression analysis.  In terms of the unit value of dimension lumber yield, the 25-, 30-, 35-, 40-, and 50-year old stands yielded about $250/mbf ($106/m3), $290/mbf ($123/m3), $330/mbf ($140/m3),  $370/mbf ($157/m3), and $450/mbf ($192/m3), respectively.  This represents an annual rate of increase in unit value yield of about $8.00/mbf ($3.42/m3) as reflected by the coefficient of X in Equation 3.  Such age-related increases in value yield could be attributed to increases or improvement in both the volume and quality of dimension lumber yields.  Table 3 shows that for the 25-, 30-, 35-, 40-, and 50-year old stands, the estimated volume of dimension lumber produced are about 16.2 mbf/acre (94.4 m3/ha.), 21.0 mbf/acre (122.4 m3/ha.), 25.9 mbf/acre (151.0 m3/ha.), 30.7 mbf/acre (179.0 m3/ha.), and 40.3 mbf/acre (235.0 m3/ha.), respectively,  of which (see Table 2) approximately 16.0 %, 36.2%, 46.7%, 49.3%, and 83.0 % graded No. 1 & better, respectively.  The annual rate of increase in volume yield is about 0.96 mbf (or 5.61 cu.m.) as reflected by the coefficient of X in Equation 2.

            Using Equation 4 and the expected total value yields per acre shown in Table 3, the time value (expressed in terms of percent incremental rate of return or R) of stumpage of loblolly pine plantations managed primarily for the production of sawtimber converted into structural dimension lumber was determined.  For instance, if the harvesting of the 25-year old stand considered in this study was deferred by 5, 10, 15, or 25 years, the R value could be about 8.5%, 7.7%, 7.1%, or 6.2%, respectively.  Similarly, if the harvesting of the 30-year old stand was deferred by 5, 10, or 20 years, the R value could be about 6.9%, 6.4%, or 5.6%, respectively.  In the case of the 35-year old stand, if its harvesting was deferred by 5 or 10 years, the R value could be about 5.9% or 4.8%, respectively.  And if the harvesting of the 40-year old stand was deferred by 10 years, the R value could be about 4.8%.  All these estimated R values are shown in Table 4.  It should be noted that these are conservative estimates because, as pointed out earlier, the value of structural dimension lumber derived from the sawtimber produced was the sole basis for the stumpage valuation.  The value of 1-inch boards and pulpwood from the top portion of the tree were not included in estimating the stumpage value.

            Evidently, the harvesting of a loblolly pine plantation stand of a given age should be deferred if the estimated R is equal to or higher than the minimum acceptable rate of return on investment or MARR whatever that is.  For example, if the MARR is 7.5% it would probably be prudent on the part of the owner of a 25-year old loblolly pine plantation stand to defer harvesting it for another 10 years because the R value then or at 35 years of age would be about 7.7%.  On the other hand, it would seem more economically desirable for owners of 30-, 35-, 40-, and 50-year old stands to do the harvesting now and not defer it to a later date because the estimated R values (see Table 4) are less than the 7.5% MARR.  Certainly, harvesting decisions have to be reviewed whenever a change in the hurdle rate or MARR occurs.  The bottom line is harvesting of the stand should be implemented only when favorable economic conditions exist or deferred to a later date whenever the expected R is equal to or higher than the MARR.

SUMMARY AND CONCLUSION

            Stumpage values of 25-, 30-, 35-, 40-, and 50-year old plantation stands of loblolly pine based solely on the volume and value (based on Summer 2000 prices) of stress-graded dimension lumber produced therefrom were determined.  Regression equations for predicting the expected total volume and value of structural dimension lumber yield per unit area (acre or hectares) of loblolly pine plantation stands were developed.  The expected yield values were used in an incremental analysis in conjunction with discounted-cash-flow techniques to determine the economic desirability of deferring the harvesting of a loblolly pine plantation stand of a given age for purposes of producing structural dimension lumber.  The following can be inferred from the results of the analysis:

1.         Structural dimension lumber volume yield of loblolly pine timber from managed plantations increases with stand age.  For 25-, 30-, 35-, 40-, and 50-year old stands like those investigated, the expected total volume yield of stress-graded dimension lumber  could be as much as 16.2 mbf/acre (94.4 m3/ha.), 21.0 mbf/acre (122.4 m3/ha.), 25.9 mbf/acre (151.0 m3/ha.), 30.7 mbf/acre (179.0 m3/ha.), and 40.3 mbf/acre (235.0 m3/ha.), respectively.  On average, the expected annual increase in volume yield could be about 0.96 mbf/acre or 5.61 cu.m./ha.

2.         The quality of loblolly pine plantation timber increases with stand age.  This was clearly reflected by the percentages (based on volume yield) of structural dimension lumber graded No. 1 & Better, which are 16.0%, 36.2%, 46.7%, 49.3%, and 83.0%, respectively, for 25-, 30-, 35-, 40-, and 50-year old stands.  This was  also reflected by the expected unit value yield of structural dimension lumber from the 25-, 30-, 35-, 40-, and 50-year old stands which are $250/mbf ($106/cu.m.), $290/mbf ($123/cu.m.), $330/mbf ($140/cu.m.), $370/mbf ($157/cu.m.), and $450/mbf ($192/cu.m.), respectively.  On average, the expected annual increase in unit value yield could be about $8/mbf ($3.42/cu.m.).

3.         Stumpage value of loblolly pine plantations based solely on the value of dimension lumber produced increases with stand age.  For 25-, 30-, 35-, 40-, and 50-year old stands like those investigated, the expected total value yield of stress-graded dimension lumber  could be as much as $4,055/acre ($10,006/ha.), $6,100/acre ($15,055/ha.), $8,531/acre ($21,140/ha.), $11,346/acre ($28,103/ha.), and $18,133/acre ($45,120/ha.), respectively.  On average, the expected annual increase in value yield could be about $566/acre  ($1,399/ha.).

4.         It would be economically desirable to defer the harvesting of a 25-year old plantation stand of loblolly pine like the one investigated by 5, 10, 15, or 25 years if the minimum acceptable rate of return on investment (MARR) is less than 8.5%, 7.7%, 7.1%, or 6.2%, respectively.  For a 30-year old stand, it would be economically desirable to defer  harvesting it by 5, 10, or 20 years if the MARR is less than 6.9%, 6.4%, or 5.6%, respectively.  For a 35-year old stand, it would be economically desirable to defer  harvesting it by 5 or 10 years if the MARR is less than 5.9% or 4.8%, respectively.  For a  40-year old stand, it would be economically desirable to defer harvesting it by 10 years if the MARR is less than 4.8%.

LITERATURE CITED

1.         American Society for Testing and Materials (ASTM).  1999.  Standard Test Methods of  Static Tests of Lumber in Structural Sizes  D 198-98.  Standard Practice for Properties of Visually Graded Lumber.  D 245-99.  Annual Book of ASTM Standards, Section 4, Vol. 04.10.  West Conshohocken, PA.

2.         Biblis, E.J. and H.F. Carino.  1999.  Flexural properties of lumber from a 50-year-old loblolly pine plantation.  Wood and Fiber Sci. 31(2):200-203.

3.         ______________________, and L. Teeter.  1998.  Comparative economic analysis of two management options for loblolly pine timber plantations.  Forest Prod. J. 48(4):29-33.

4.         ______________________, and R. Brinker.  1997.  Flexural properties of lumber from two 40-year-old loblolly pine plantations with different stand densities.  Wood and Fiber Sci. 29(4):375-380.

5.         ___________________________________.  1995.  Effect of stand density on flexural properties of lumber from two 35-year-old loblolly pine plantations.  Wood and Fiber Sci. 27(1):25-33.

6.         ___________________________________,  and C.W. McKee.  1993.  Effect of stand age on flexural properties and grade compliance of lumber from loblolly pine plantation timber.  Forest Prod. J. 43(2):23-28.

7.         Carino, H.F. and E.J. Biblis.  2000.  Comparative analysis of the quality of sawlogs from 35-, 40-, and 50-year-old loblolly pine plantation stands.  Forest Prod. J. 50(11/12):48-52.

8.         Pearson, R.G. and R.C. Gilmore.  1971.  Characterization of the strength of juvenile wood of loblolly pine (Pinus taeda L.).  Forest Prod. J. 21(1):23-30.

9.         Southern Pine Inspection Bureau.  1994.  Grading rules.  SPIB, Pensacola, FL.

10.       Schultz, R.P.  1997. Loblolly Pine: The Ecology and Culture of Loblolly Pine (Pinus taeda L.).  Agri. Handb. 713, Chapter 1. USDA Forest Serv., Washington, D.C., p. 3.

11.       Zobel, B.J. and D.G. Kirk.  1972.  Wood properties of young loblolly and slash pines.  In: Proc. Symp. on the Effect of Growth Acceleration on the Properties of Wood.  USDA Forest Serv., Forest Prod. Lab., Madison, Wis.

12.       _________ and R. Blair.  1976.  Wood and pulp properties of juvenile wood and topwood of the southern pines.  In: Proc. 8th Cellulose Conf. Applied Polymer Symp. 28:421-433.

Table 1.  Characteristics of 25-, 30-, 35-, 40-, and 50-year old loblolly pine (Pinus taeda L.) stands considered in this study.

           


Table 2.            Expected percent distribution of stress-graded dimension lumber from 25-, 30-, 35-, 40-, and 50-year old loblolly pine plantation stands1.

1Stress grades are based on SPIB allowable design values of "Fb" and "E" as listed in Tables 1a, 1b, and 1c, pages A3, A4, and A5 of Standard Grading Rules for Southern Pine Lumber, 1994 (9).

Table 3.            Expected volume and value yields of stress-graded dimension lumber from 25-, 30-, 35-, 40-, and 50-year old loblolly pine plantation stands1.

1The expected values of unit value and total volume were calculated using Equations 2 and 3, respectively, and the expected value yield per acre is the product of the two.

Table 4.            Expected time-value (or incremental rate of return) of stumpage of loblolly pine plantations of various ages managed for sawtimber production when harvesting is deferred1.

            1In this case, stumpage is based on the value of stress-graded dimension lumber product yield. Stress grades are based on SPIB allowable design values of "Fb" and "E" as listed in Tables 1a, 1b, and 1c, pages A3, A4, and A5 of Standard Grading Rules for Southern Pine Lumber, 1994 (9).