Structural Lumber

Properties of

Hybrid Poplar

David E. Kretschmann

J.G. Isebrands

Glen Stanosz

John R. Dramm

Adele Olstad

David Cole

Jay Samsel

United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Research

Paper

FPL-RP-573
Abstract

The Lake States of Michigan, Minnesota, and Wisconsin consist

of 49.4 million hectares (122 million acres) of land, 19.8 million hectares (49 million acres) of which are forested, with 6%

of those having been removed by law from timber production.

Aspen (Populus tremuloides) is an important component of this

resource. In recent years, a concern that the aspen cut will

exceed its growth has surfaced. That is, Will the aspen supply

be adequate to support the growing solid-wood, composite, and

paper industries in the Lake States region? To satisfy the increased demand for forest products, it is expected that much of

the future timber supply will be from improved trees grown on

managed plantations. It is critical that the mechanical properties

of this resource are clearly understood so that alternative uses of

this material can be evaluated. A study was conducted using

full-size lumber tests on 243 38- by 89-mm (2- by 4-in.; hereafter called 2 by 4’s) boards cut, using two methods, from 50

logs to determine selected mechanical and physical properties of

the Wisconsin-5 hybrid poplar clone. The material was either

kiln dried or partially air dried followed by kiln drying. The

2 by 4’s were assigned grades according to four grading rules:

Light Framing, Structural Light Framing, Structural Lamination,

and Machine Stress Rating. Results suggest that this poplar

clone would produce visually graded material that is similar in

properties and characteristics to the native aspen and cottonwood resource. Close to 65% of the material produced made

grades of either Standard and better or No. 2. The Machine

Stress Rating grade most likely to be produced from this material would be 1450f–1.3E. To avoid excessive degrade as a

result of warping during drying, this material should be dried in

flitch form.

Keywords: hybrid poplar, mechanical properties, bending, MSR

January 1999

Kretschmann, David E.; Isebrands, J.G.; Stanosz, Glen; Dramm, John R.;

Olstad, Adele; Cole, David; Samsel, Jay. 1999. Structural lumber properties

of hybrid poplar. Res. Pap. FPL–RP–573. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory. 8 p.

A limited number of free copies of this publication are available to the

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Contents

Page

Introduction................................................................................ 1

Background ................................................................................ 1

Experimental Methods ............................................................... 2

Material Selection .................................................................. 2

Log Scale ............................................................................... 2

Sawing ................................................................................... 2

Drying .................................................................................... 3

Test Procedures...................................................................... 3

Results........................................................................................ 3

Sawing Yields ........................................................................ 3

Visual Grades......................................................................... 3

Mechanical Properties............................................................ 4

Comparison With Other Visual Grade Data........................... 4

Sawing and Drying Effects on Warp...................................... 4

Property Relationships ........................................................... 6

Machine Stress Rating ........................................................... 6

Discussion .................................................................................. 6

Conclusions................................................................................ 7

References.................................................................................. 7
Structural Lumber Properties

of Hybrid Poplar

David E. Kretschmann, Research General Engineer

Forest Products Laboratory, Madison, Wisconsin

J.G. Isebrands, Project Leader

North Central Research Station, Rhinelander, Wisconsin

Glen Stanosz, Assistant Professor

Plant Pathology, Univeristy of Wisconsin—Madison, Wisconsin

John R. Dramm, Wood Technologist

Adele Olstad, Computer Assistant

FPC&R Technology Marketing Unit, Forest Products Laboratory, Madison, Wisconsin

David Cole, President

Independent Technical Agricultural Consulting, Prairie du Sac, Wisconsin

Jay Samsel, Sawmill Manager

Samsel LTD, Hancock, Wisconsin

Introduction

The Lake States of Michigan, Minnesota, and Wisconsin

consist of 49.4 million hectares (122 million acres),

19.8 million hectares (49 million acres) of which are forested. An important component of this resource is trembling

aspen (Populus tremuloides). There is concern that the aspen

cut will exceed growth, and the aspen supply will not be

adequate to support the growing solid-wood, composite, and

paper industries in the Lake States region (Youngquist and

Spelter 1989). To satisfy the increased demand for forest

products, it is expected that much of the future timber supply

will be from improved trees grown on managed plantations.

This fast-growth resource tends to be harvested in short

rotations, if these trees follow the trend of similar species

(Bendtsen and Senft 1986), and it will contain greater proportions of juvenile wood compared with current harvests. It

is critical that the mechanical properties of this resource are

clearly understood so that the proper uses of this material can

be determined.

Background

In the past, most harvested aspen was used for pulp, lumber,

hardboard, and insulation board. With the introduction of

waferboard and oriented strandboard (OSB), aspen utilization increased threefold from 1975 to 1989 (Youngquist and

Spelter 1990) and is now five times greater than the 1975

level (McKeever and Spelter 1998). During the past 30

years, much work has been conducted in forest genetics on

Populus species (Riemenshneider and others 1996a,b) to

develop improved hybrids. Several experimental plots have

been planted across the Lake States to investigate improved

Populus clones. In most improvement programs, the focus

has been on growth rate, form, adaptability, and disease

resistance. Additional emphasis needs to be placed on the

effect of improvements on utilization properties of the material. It is possible that wood from these hybrids that have

been developed to have superior growth, improved form,

adaptability, and improved fiber characteristics for paper

may be less suited to solid-wood processing than wood from

either parent tree. Some work has been done to investigate

the mechanical properties of hybrid poplars (Bendtsen and

others 1981, Hall and others 1982), but many hybrid types

are being developed and planted on experimental plots and

each has its structural characteristics.

One such series of experiment hybrid poplar plots was

planted at the University of Wisconsin–Madison, Hancock

Agricultural Experiment Station. In the late 1970s, Wisconsin-5 hybrid poplar trees were planted in several experimental plots as windbreakers to protect potato fields. The parentage of Wisconsin-5 is a mystery; it is thought to be a hybrid

tree that was found in someone’s yard in a small Wisconsin

town. Wisconsin-5 probably originated in Europe and was

brought to North America by immigrants. In these experimental plots, special silvicultural measures were not applied

to the hybrid poplar trees. This material was harvested in the

winter of 1996–1997 to make more room for larger agricultural plots. The material that was cut offered a good opportunity to analyze the material properties of a common clonetype planted in Wisconsin.
2

The objective of this study was to investigate the mechanical

and physical properties of the Wisconsin-5 hybrid poplar

clone and compare those properties with previously full-size

(In-Grade) properties of native aspen and cottonwood.

Experimental Methods

Material Selection

Three plots of hybrid poplar were harvested at the University

of Wisconsin–Madison Hancock Agricultural Experiment

Station during the winter of 1996–1997. Approximately

600 trees were harvested, resulting in more than 2,000

2.7-m- (9-ft-) long logs. These logs ranged from 76 to

330 mm (3 to 13 in.) in small-end diameter. Fifty saw logs

were selected from these logs, which had a small enddiameter range of 95 to 292 mm (6.75 to 11.5 in.). The logs

were selected based on limb size and log diameter. An effort

was made to select only logs that would be representative of

material grown in a plantation setting where the crown

closure would limit limb size development. Therefore, logs

with limbs greater than 152 mm (6 in.) in diameter were not

selected. Detailed information on length, small-end minimum

and maximum diameters, and large-end minimum and maximum diameters was recorded for each log. This information

was used to sort the 50 logs into two roughly equivalent

groups (A and B) based on diameter. A summary of the

dimensions of these logs is given in Table 1. The actual

length of the log varied from 2.4 to 3.0 m (7.9 to 9.7 ft).

Log Scale

This diameter information was then used to determine an

estimate of the expected number of cubic meters (board feet)

of 2 by 4’s to be produced using the IMPROVE system log

analysis routine (USDA 1990b) and Best Opening Face

sawing simulation analysis routine (USDA 1990a). The

predicted values based on Scribner Decimal-C log scale and

the Best Opening Face sawing simulation are given in

Table 2.

Sawing

The sawing was done at a sawmill in Hancock, Wisconsin, in

June 1997. The first group of 25 logs was cut directly into

2 by 4’s (Fig. 1A). The actual dimensions of the green

2 by 4’s were 44 mm (1.75 in.) thick and, because of limited

settings on the edger, a full 102 mm (4 in.) wide.

The other group of 25 logs was cut using the Saw–Dry–Rip

method (Boone 1990; Maeglin 1990). The logs were cut into

Table 1—Summary of log diameter information for group A and B logs

Mean Minimum Maximum

Diameter

A

mm (in.)

B

mm (in.)

A

mm (in.)

B

mm (in.)

A

mm (in.)

B

mm (in.)

Small-end minimum 214

(8.43)

213

(8.42)

171

(6.75)

178

(7.00)

267

(10.5)

292

(11.5)

Small-end maximum 224

(8.83)

222

(8.76)

1.84

(7.25)

184

(7.25)

279

(11.0)

292

11.5

Large-end minimum 248

(9.76)

251

(9.87)

190

(7.5)

203

(8.0)

330

(13.0)

356

(14.0)

Large-end maximum 263

(10.34)

264

(10.40)

210

(8.25)

203

(8.0)

356

(14.0)

375

(14.75)

Table 2—Cubic meters (board feet) of poplar logs

Number

of logs

Scribner

Decimal-C

(min/max) cubic

meters (board feet)

Predicted

number

of

2 by 4’s

Predicted

cubic meters

(board feet)

Actual

number

of

2 by 4’s

Cubic meters

(board feet)

nominal dry

lumber tally

Group A

(2 by 4)

25 0.99 (420) 140 1.76 (747) 110 1.39 (587)

Group B

(flitch)

25 0.99 (420) 145 1.82 (773) 133 1.68 (709)

Total 50 1.98 (840) 285 3.58 (1,520) 243 3.07 (1,296)
3

44-mm- (1.75-in.-) thick flitches of random width (Fig. 1B).

The green material from the two methods of sawing was

combined and stickered in two equivalent groups. These

flitches were edged to provide a more compact kiln load.

The edging was sufficient to square up the edge of the flitch

and to remove “butt flare” but did not remove considerable

wane. The stickering method is shown in Figure 2. Wider

flitches were kept to the outside of the stacks, and the

2 by 4’s were stacked in the interior.

Drying

The material was dried between June and August of 1997.

Two methods of drying were used. First, a combination of

group A and B material was placed in the dry kiln immediately after sawing under a maximum temperature of 54o

C

(130o

F). A second combination of group A and B material

was placed outside for an initial air drying of 1.5 months

before kiln drying.

Test Procedures

The dry poplar was shipped to the USDA Forest Service,

Forest Products Laboratory (FPL), for additional processing

into kiln-dried 38- by 89-mm (1.5- by 3.5-in.) lumber. The

poplar was then graded by a quality supervisor from the

West Coast Lumber Inspection Bureau (WCLIB) using four

grading rules: Light Framing, Structural Light Framing,

Lamination, and Mechanical Stress Rated lumber. Detailed

information on the poplar was recorded for warp characteristics (crook, bow, and twist) and defect locations. Just prior to

testing, a transverse vibration dynamic modulus of elasticity

(MOE) was determined for each board. The material was

tested in bending according to D4761 (ASTM 1996). Data

were collected on modulus of rupture (MOR), MOE, specific

gravity, and moisture content according to D2395 (ASTM

1996).

Results

The following sections summarize results for sawing yields,

the four grading systems investigated, mechanical properties,

machine stress rating potential, and sawing and drying effects

on warp.

Sawing Yields

The two far right columns of Table 2 show the actual and

nominal lumber tallies of 2 by 4’s produced and the cubic

meters (board feet) of the study logs. The large difference

between the predicted and actual volume was due to the

width limitations on the edger.

Visual Grades

Table 3 shows the breakdown of visual grades by group

and total. In the Light Framing grades, the majority of the

material was Construction grade. In the Structural Light

A B

Figure 1—Two sawing patterns were used:

(A) 2 by 4 and (B) flitch.

Figure 2—Stacking procedure used to dry kiln was wide

flitches on the exterior and 2 by 4’s on the interior.

Table 3—Number of pieces by visual grade and group

A B

Grade 2 by 4 Flitch Total

Light Framing

Construction 69 53 122

Standard 17 28 45

Utility 15 27 42

Economy 9 25 34

All 110 133 243

Structural Light Framing

SS. 31 25 56

No. 1 31 25 56

No. 2 19 30 49

No. 3 19 29 48

Economy 10 24 34

All 110 133 243

Structural Lamination

L1 37 41 78

L2 28 29 57

L3 23 12 35

Reject 22 51 73

All 110 133 243
4

Framing grades, slightly less than half the material was

No.1 or better. In the Structural Lamination grades, about the

same amount of material was in the top grade as was rejected. These results suggest that a sizeable amount, more

than 65%, of the material cut from the hybrid poplar logs,

would make either Light Framing grades of Standard or

better or Structural Light Framing grades of No. 2 or better.

Mechanical Properties

The mechanical property results for Light Framing and

Structural Light Framing are summarized in Table 4. The

results are presented by grade and overall. The relationships

of dynamic MOE to static edgewise MOE and edgewise

MOE to MOR are also presented. Dynamic MOE is a

method of determining MOE for the entire length of the

board using the flatwise vibrational frequency of the board.

Edgewise MOE is determined by measuring the deflection of

the board while under edgewise loading. For this sample,

long-span flatwise dynamic MOE tended to be greater than

the measured edgewise static MOE.

Comparison With Other

Visual Grade Data

The comparison of hybrid poplar with native aspen and

cottonwood is of particular interest to potential hybrid poplar

lumber producers. To make the comparison, the Select

Structural and No. 2 test results for hybrid poplar were compared with the 2 by 4 aspen and cottonwood values in the

National Design Specification Supplement (NDS) (AF&PA

1997) and the North American In-Grade Testing Program

results for aspen–cottonwood (Green and Evans 1987).

Table 5 displays the results of this comparison. The results

suggest that Wisconsin-5 poplar would produce visually

graded material that is similar in properties and characteristics to current NDS aspen and cottonwood values but less

than In-Grade results for aspen–cottonwood.

Sawing and Drying Effects on Warp

Warp characteristics were measured to the nearest 0.79 mm

(0.031 in.). The allowable warp for a 2.44-m (8-ft) long

2 by 4 according to the WCLIB grading rule is listed in

Table 6.

Table 4—Summary of mechanical property test results

Grade

Moisture

content

(%)

COV

(%)

Specific

gravitya COV

(%)

Avg dynamic

MOE (GPa)

(106

lb/in2)

COV

(%)

Avg MOE

(GPa)

(106

lb/in2)

COV

(%)

Avg MOR

(MPa)

 (103

 lb/in2)

COV

(%)

5th % MOR

(MPa)

(103

 lb/in2)

Light Framing

Construction 10.8 2.8 0.40 6.8 10.8

(1.57)

14.3 9.2

(1.34)

15.2 42.4

(6,147)

28.9 23.1

(3,357)

Standard 10.7 3.0 0.40 7.0 9.8

(1.43)

20.3 8.5

(1.24)

20.4 37.1

(5,376)

37.0 16.0

(2,324)

Utility 10.8 2.7 0.41 8.6 10.1

(1.46)

20.7 8.4

(1.22)

23.0 37.5

(5,442)

37.0 11.5

(1,667)

Economy 10.7 3.4 0.40 6.8 9.2

(1.34)

21.0 8.4

(1.22)

22.9 36.3

(5,273)

37.6 14.1

(2,051)

Structural

Light Framing

SS. 10.7 2.7 0.39 5.8 11.5

(1.67)

10.7 9.7

(1.40)

14.7 45.1

(6,542)

24.0 27.0

(3,923)

No. 1 10.8 2.9 0.40 7.9 10.2

(1.48)

16.1 8.9

(1.29)

15.2 40.0

(5,795)

29.4 23.0

(3,331)

No. 2 10.7 3.0 0.40 7.6 10.1

(1.46)

19.5 8.7

(1.26)

19.9 37.4

(5,421)

40.8 15.2

(2,204)

No. 3 10.8 2.5 0.41 7.8 10.1

(1.46)

19.7 8.5

(1.23)

20.4 39.3

(5,697)

31.5 18.9

(2,742)

Economy 10.7 3.5 0.40 6.7 9.4

(1.36)

21.4 8.3

(1.21)

24.7 34.4

(4,992)

42.1 9.8

(1,415)

All 10.8 0.40 10.3

(1.50)

8.9

(1.29)

39.7

(5,760)

18.3

(2,662)

a

Specific gravity based on ovendry weight volume at time of test.
5

Table 6—Amount of allowable warp according to the

West Coast Lumber Inspection Bureau grading rule

Allowable warp for grade of lumber (mm (in.))

2 by 4

material Bow Crook Twist

No. 1 13 (0.50) 6 (0.25) 9 (0.375)

No. 2 19 (0.75) 9 (0.375) 13 (0.50)

No. 3 25 (1.0) 13 (0.50) 19 (0.75)

Table 7—Percentage of pieces that were rejected for warp

Bow (%) Crook (%) Twist (%)

Drying method n No.1 No. 2 No. 3 No. 1 No. 2 No. 3 No. 1 No. 2 No. 3

2 by 4 air dry 43 0 0 0 41.9 18.6 7.0 0 0 0

Flitch air dry 80 3.7 1.2 0 11.1 1.2 0 0 0 0

2 by 4 kiln dry 56 3.6 0 0 26.8 14.3 3.6 0 0 0

Flitch kiln dry 64 6.3 1.6 0 12.5 3.1 0 0 0 0

Table 7 is a summary of the warp characteristics measured on

the cut material. The numbers shown represent the percentage of all pieces that did not make the warp characteristic

specified for a given grade in the WCLIB grading rule.

None of the boards had problems making a grade because

of twist, and only a few pieces would have been eliminated

from No.1 because of bow. The sawing method had a

significant impact on the number of pieces eliminated from a

grade category. There was considerable improvement in the

crook characteristics of the material allowed to dry in flitch

form. In addition, kiln drying can substantially reduce the

amount of crook problems.

Table 5—Comparison of Wisconsin-5 poplar study results to other existing 2 by 4 full-size data

Grade Sample

Moisture

content (%)

Specific

gravitya

MOE (GPa)

(×106

 lb/in2)

5th % MOR

(MPa) (lb/in2

)

Select Structural Hybrid poplar 11 0.41 9.7 (1.4) 27.0 (3,920)

NDSb aspen 12 0.39 7.6 (1.1) 19.0 (2,760)

NDS cottonwood 12 0.41 8.3 (1.2) 19.0 (2,760)

In-Grade aspen–

cotttonwood

12 0.43 10.3 (1.5) 35.8 (5,190)

No. 2 Hybrid poplar 11 0.42 8.7 (1.3) 15.2 (2,200)

NDS aspen 12 0.39 6.9 (1.0) 13.0 (1,890)

NDS cottonwood 12 0.41 7.6 (1.1) 13.6 (1,970)

In-Grade aspen–

cotttonwood

12 0.46 9.0 (1.3) 22.1 (3,200)

a

Specific gravity based on ovendry weight and ovendry volume.

b

AF&PA 1997.
6

Property Relationships

Dynamic MOE–MOE Relationship

The relationship between dynamic MOE and static edgewise

MOE is shown in Figure 3. The lower than expected r2

 value

(r2

 = 0.58) can partially be explained by the limited range of

MOE data. Normally an r2

 value between dynamic MOE and

edge MOE would be in the range of 0.7 to 0.85 or greater.

However, dynamic MOE can clearly be used as a predictor

of edgewise MOE.

MOE–MOR Relationship

The MOR was positively correlated to edgewise MOE,

and the r2

 value (r2 = 0.42) was similar to other r2 values

reported for hardwoods (Green and others 1994).

The relationship between static edgewise MOE and

MOR is shown in Figure 4. The relationship shown is

satisfactory for the development of machine-stress-rated

(MSR) lumber.

Machine Stress Rating

Machine stress rating (MSR) is a type of machine-graded

lumber. Such lumber is evaluated by a machine using a nondestructive test followed by visual grading to limit certain

characteristics that the machine cannot detect or may not

properly evaluate. This material is often used in demanding

engineering applications that require reduced variability and

assurance of a particular minimum bending strength level.

The following procedure was used to simulate possible MSR

grades. All material that did not meet the No. 2 warp and

wane requirements was eliminated. The remaining pieces

were ranked by static edgewise MOE. Boundaries were then

selected based on 0.82 times the average target MOE. This

boundary was shifted upward in cases where, based on this

boundary, the average MOE for the remaining test data

would have been too low for the target average MOE of the

selected grade until the average MOE for the remaining test

data was obtained. After the MOE level was established, the

pieces that failed to make targeted bending strength values

were counted to ensure that the criteria for 5th percentile

estimation with 75% tolerance outlined in D2915 (ASTM

1996) were met.

The highest grade possible would most likely be a 1800f–

1.5E grade. With this grade, slightly more than 33% of

pieces would make a grade of 1800f–1.5E (81 of 243

pieces). Decreasing the strength level to 1650f would not

improve the yield because this particular sort was controlled

by MOE, not MOR. Visually, this material had a high

percentage of small knots. However, the stiffness of this

material would probably support only an MSR grade with an

associated MOE level of 1.0 GPa (1.5 ×106

 lb/in2). A second

sort indicated that 60% of the material could be placed in a

lower grade of 1450f–1.3E (147 of 243 pieces).

Discussion

The objective of this study was to investigate the structural

potential of a hybrid poplar, Wisconsin-5. Results suggest

that the material is suitable for construction lumber with

properties similar to those of aspen and cottonwood. The use

of this material in trusses would most likely be limited to web

members because only a small portion of the material had

high levels of strength and stiffness. However, the material

could be used for light framing applications; in particular,

studs of walls. The sample that we obtained came from a

relatively open-grown stand and had several large knots.

Therefore, there is the potential that even higher grade yields

could be obtained from each log if different management

techniques were used.

Figure 3—Relationship between dynamic MOE and

edgewise static MOE.

Figure 4—Relationship of edgewise MOE to MOR.
7

Although the objective of this study was not to conduct a

yield study, there were substantial yield differences, nearly

20% between the actual and simulated lumber recoveries.

Differences between actual and Best Open Face simulated

lumber recovery suggest the potential increases that can be

made with more efficient handling of the material. Although

there were problems with proper log trim allowances (over

and under length), the majority of the lower actual lumber

recovery was due to the fact that the study logs in group A

were sawn to a 44- by 102-mm (1.75- by 4-in.) size. Better

control of log-over-length and lumber width and thickness

would increase lumber recovery substantially.

Another observed characteristic of the material harvested was

a significant dark brown discoloration of the heartwood

(Fig. 5). The drying process moderated this discoloration.

This mottled look could be an attractive character mark in

paneling or cabinetry.

The wood was very easy to process in the sawmill. Drying

was the most difficult aspect of producing the structural

lumber. However, when the wood is dried in flitch form,

significant improvements can be made in the warp characteristic of the final lumber produced.

Conclusions

The following conclusions about Wisconsin-5 hybrid poplar

were drawn as a result of this study:

• 65% of this type of sawn material will fall in the visual

grades of either Standard and better or No. 2

and better.

• This poplar clone produces visually graded material

that is similar in properties and characteristics to current

visually graded native aspen and cottonwood.

• 60% of this sawn material will fall in an MSR grade of

1450f–1.3E.

• To avoid excessive degrade as a result of warping during

drying, this material should be dried in flitch form.

The application of this type of material for furniture, millwork, and paneling will be investigated. Additional work is

needed to determine if some hybrids have less of a discolored

core than do other hybrids. In addition, it would be good to

test other hybrids and planting density.

References

AF&PA. 1997. National Design Specification Supplement.

Washington DC: American Forest and Paper Association.

ASTM. 1996. Philadelphia, PA: American Society for

Testing and Materials.

D2915. Standard practice for evaluating allowable

properties for structural lumber.

D2395-93. Standard test methods for specific gravity of

wood and wood-based materials.

D4761. Standard test methods for mechanical properties of

lumber and wood-based structural material.

Bendtsen, B.A.; Maeglin, R.R.; Deneke, F. 1981. Comparison of mechanical and anatomical properties of eastern

cottonwood and populus hybrid NE–237. Wood Science.

14(1).

Bendtsen, B.A.; Senft, J. 1986. Mechanical and anatomical

properties in individual growth rings of plantation-grown

eastern cottonwood and loblolly pine. Wood and Fiber

Science. 18(1): 23–38.

Boone R.S. 1990. Sorting aspen bolts and drying aspen

flitches for SDR. NC–GTR–140. Aspen symposium 89.

St. Paul, MN: U.S. Department of Agriculture, Forest

Service, North Central Forest Experiment Station: 295–299.

Green, D.W.; Evans, J.W. 1987. Mechanical properties of

visually graded lumber: National Technical Information

Service. Vol. 1. Figure 5— Discoloration observed in logs (top)

and boards (bottom).
8

Green, D.W.; Ross, R.J.; McDonald K.A. 1994. Production of hardwood machine stress rated lumber. In: Proceedings, 9th International symposium on nondestructive testing

of wood; 1993 September 22–24; Madison, WI. Madison,

WI: Forest Products Society: 141–150.

Hall, R.B.; Hilton, G.D.; Maynard, C.A. 1982. Construction lumber from hybrid aspen plantations in the central

states. Journal of Forestry, Society of American Foresters:

291–294 (May).

Maeglin, R.R. 1990. Structural lumber from aspen: using the

SAW–DRY–RIP (SDR) process. NC–GTR–140. Aspen

symposium 89. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station: 283–293.

McKeever, T.; Spelter, H. 1998. Wood-based panel plant

locations and timber availability in selected U.S. states. Gen.

Tech. Rep. FPL–GTR–103. Madison, WI: U.S. Department

of Agriculture, Forest Service, Forest Products Laboratory.

Riemenschneider, D.E.; Netzer, D.A.; Berguson, B.

1996a. Intensive culture of hybrid poplars: what’s new in

Minnesota. In: Stokes, B.J., ed. Proceedings, 1st conference,

Short Rotation Woody Crops Operations Working Group;

1996 September 23–25; Paducah, KY. Auburn, AL: Auburn

University: 53–58.

Riemenschneider, D.E.; Stelzer H.E.; Foster G.S. 1996b.

Quantitative genetics of poplars and poplar hybrids. In:

Biology of populus and its implications for management and

conservation. Part I, Chap. 7. Ottawa, ON: NRC Research

Press, National Research Council Canada: 159–181.

USDA. 1990a. Best opening face sawing simulation analysis

routine. Madison, WI: U.S. Department of Agriculture,

Forest Service, State and Private Forestry, Forest Products

Laboratory, Madison, WI. Version 2.0.

USDA. 1990b. Log analysis routine, IMPROVE system log

processing program. Madison, WI: U.S. Department of

Agriculture, Forest Service, State and Private Forestry,

Forest Products Laboratory, Madison, WI. Version 1.1.

Youngquist, J.A.; Spelter, H. 1990. Aspen wood products

utilization: impact of the Lake States composites industry.

NC–GTR–140. Aspen symposium 89. St. Paul, MN: U.S.

Department of Agriculture, Forest Service, North Central

Forest Experiment Station: 91–102.