United States

Department of 

Agriculture

Forest Service

Northern 

Research Station

Research Paper NRS-2

Long-term Assessment 

of Financial Maturity, 

Diameter-limit Selection 

in the Central Appalachians

Thomas M. Schuler 

David W. McGill
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Abstract

Simple diameter-limit cutting is an exploitive harvesting technique that contributes to lower 

stand values and has depleted high-quality sawlog resources in the central Appalachian 

region. Financial maturity, diameter-limit (FMDL) selection was proposed more than three 

decades ago as a replacement for diameter-limit cutting. FMDL incorporates financial 

maturity guidelines for individual trees, high-priority removal of poor-quality trees, and 

guidelines for residual basal area (RBA). We provide the first long-term assessment of this 

practice. Three levels or rate-of-return treatments (3, 4, and 6-percent) were replicated twice 

on 240 acres. We compared these treatments after three to four 10-year periodic harvests 

with respect to board foot productivity, RBA, butt-log quality, and species composition. The 

3- and 6-percent treatments were the most disparate after three periodic harvests yielding 

278 and 523 board feet/acre/year, respectively. The 6-percent treatment averaged 445 board 

feet/acre/year after the fourth periodic harvest. RBA did not differ significantly by treatment 

or harvest period, though postharvest basal area usually was less than the heretofore 

previously recommended minimum of 55 ft2

/acre for sawlog-size trees. Butt-log quality did 

not differ by the experimental design but on average was stable or improving through time 

for all three treatments. Composition in all three treatments was increasingly dominated by 

shade-tolerant species. Empirical evidence suggests that lowering the minimum RBA of 

sawlog-size trees to 45 ft2

/acre on good sites (SI 65 to 74) is required to implement the 6-

percent rate of return treatment.

Manuscript received for publication 7 August 2006

Cover Photo

Fernow Experimental Forest, compartment 20B, camera point 5 in 2006 after three decades 

of FMDL selection using 4-percent rate-of-return guidelines
1

INTRODUCTION

Diameter-limit cutting is the dominant type of timber 

harvesting on the vast network of nonindustrial private 

forests (NIPF) in the Eastern United States (Fajvan 

and others 1998; Nyland 2001). Positive attributes 

of this method include periodic cash fl ow, little to no 

investment, and retention of standing green trees that 

mitigates the visual effects of harvesting and provides 

residual growing stock for the next cycle of stand growth. 

However, in practice, diameter-limit cutting ignores goals 

for residual stocking and seldom removes poor-quality 

trees. Throughout the Appalachians, 12 inch diameter 

at breast height (d.b.h.) or stump-diameter limits of 14 

inches often are used because trees of this size generally 

return a profi t but also contribute to lower stand values 

(Smith 1980; Nyland 2005).

In West Virginia, diameter-limit cutting was ranked 

by service foresters as one of the most severe forest 

management practices (McGill and others 2004). In 

Ohio, Pennsylvania, and West Virginia alone, 22.5 

million acres of timberland recently were classifi ed as 

sawtimber-size stands (http://www.fs.fed.us/ne/fi a/states, 

18 January 2006). It is this type of stand that is at risk or 

already has been subjected to exploitive and unsustainable 

timber harvesting (Fajvan and others 1998) that disrupts 

a continuous output of desired products and degrades 

future productivity on the site.

Empirical studies spanning up to 50 years generally 

have confi rmed the observed negative effects of repeated 

diameter-limit cutting. Reduced growth through 

time and a reduction in residual stem quality were 

documented by Sokol and others (2004), Kenefi c and 

others (2005), and Ward and others (2005). However, 

growth trends are not always negative and may depend 

on the initial stand structure and the random nature 

of the spatial and size distribution of residual stems 

following diameter-limit cutting (Schuler 2004). During 

the onset of trials using diameter-limit cutting, revenue 

generation and compounded rates of return are higher 

than other partial cutting practices, but residual stand 

values usually are lower (Miller 1993; Kenefi c and others 

2005). Nyland (2005) used computer simulation to 

evaluate the long-term effects of this cutting practice. He 

concluded that the only advantage with diameter-limit 

cutting is the high volume and value produced during the 

fi rst harvest cycle of a well-stocked, uneven-aged stand.

Negative perceptions of diameter-limit cutting should be 

tempered by the fact that most timber harvests (including 

those in trials) that remove trees based on diameter 

alone make no minimum residual stand specifi cations 

or prescribe other treatments to the harvested stand 

that might counteract the associated negative effects 

of this cutting practice. For example, some practices 

that are reported as diameter-limit cuts have such low 

diameter limits (Erdmann and Oberg 1973; Strong and 

others 1995; Niese and others 1995) that they might 

be considered “commercial clearcuts” which remove 

all useable stems, usually to about 5 inches d.b.h. 

Even selection systems with harvesting guidelines that 

prioritize the elimination of cull or lower quality trees can 

result in diameter limit-like residual stands if the initial 

stand has a high proportion of large remnant culls from 

previous cuttings (Orr and others 1994). By contrast, 

modeling research in northern and southern hardwood 

forest types revealed that diameter-limit cutting may be 

sustainable for some forest management objectives (Volin 

and Buongiorno 1996; Buongiorno and Vasievich 2000; 

Buongiorno and others 2004).

The Authors

THOMAS M. SCHULER, research forester, received 

an M.S. degree in silviculture from Colorado State 

University and a Ph.D. degree in forest biology from 

Purdue University. He is currently engaged in research 

on the ecology and silviculture of Appalachian hardwood 

forests and the restoration of central Appalachian spruce 

forests at the Northern Research Station’s Timber and 

Watershed Laboratory at Parsons, West Virginia.

DAVID W. McGILL, extension specialist and associate 

professor of forest resources at West Virginia University, 

received an M.S. degree in forestry from the University 

of Wisconsin at Madison and a Ph.D. degree in forest 

resources management from Pennsylvania State 

University. He is currently responsible for forestry 

outreach education and applied forest resources research 

with the Appalachian Hardwood Center, a unit of the 

WVU Extension Service and Davis College of Agriculture, 

Forestry, and Consumer Sciences. 
2

Trimble and others (1974) proposed a silvicultural 

alternative to diameter-limit cutting and the seldom used 

and more complex single-tree selection that combined 

periodically harvesting individual sawlog-size trees at 

fi nancial maturity, an improvement cut at each harvest 

cycle, and guidelines for residual basal area (RBA). Trimble 

referred to this type of silviculture as fi nancial maturity, 

diameter-limit (FMDL) selection. Referring to this type 

of harvesting as a variant of diameter-limit cutting may 

be inappropriate because the FMDL method requires the 

removal of not only cull but also trees of poor vigor and 

poor quality, some control of species composition, and 

guidelines for RBA. Thus, FMDL also can be considered a 

variant of an uneven-age selection system.

The FMDL process of determining the fi nancial maturity 

of individual trees is based on site index (SI), tree size, 

conversion costs, lumber values, and associated species 

values (Mendel and Trimble 1969; Trimble and Mendel 

1969; Grisez and Mendel 1972; Mendel and others 

1973). Although fi nancial maturity guidelines will change 

with technology and markets, it is not our intent to 

evaluate species-specifi c, fi nancial maturity guidelines. 

However, if the silvicultural approach proves sustainable, 

periodic updates to the fi nancial maturity guidelines 

should be developed for regional markets to refl ect more 

current conditions. In reviewing practical considerations 

when applying FMDL, Miller and Smith (1993) 

concluded that most of the objectives of single-tree 

selection can be achieved with this approach. Here, we 

expand on existing research by providing the fi rst longterm comparison of three harvest intensities using FMDL. 

We compare merchantable yield, residual stocking, 

quality of harvested logs, and species composition over 

time for up to three 10-year cutting cycles and four 

periodic harvests, and discuss management implications, 

potential silvicultural improvements, and future research 

needs.

FINANCIAL MATURITY DIAMETERLIMIT SELECTION

With FMDL, a stand-improvement operation is carried 

out and sawtimber-size trees that fall below a desired 

rate of return are harvested. Trees that exceed a specifi ed 

rate of return are left to grow and appreciate in value, 

assuming a 10- to 15-year cutting cycle. Financial 

maturity guidelines for individual trees have been 

developed based on species, SI, and desired rate of return 

(Appendix). In addition to removing trees that are 

fi nancially mature, an improvement cut is prescribed at 

each periodic harvest to improve residual stand quality 

(Appendix). Poor-quality or high-risk trees designated 

for removal have low or negative rates of return and 

occupy growing space that could be used for establishing 

new regeneration and/or used by trees with better rates 

of return. In practice, it has been recommended that the 

improvement cut should be estimated fi rst and then the 

rate-of-return marking guideline selected to achieve the 

desired RBA in sawlog-size trees as follows: SI 80: 70 to 

85 ft2

/acre, SI 70: 55 to 70 ft2/acre, SI 60: 40 to 55 ft2/

acre (Trimble and others 1974; Miller and Smith 1993). 

Stands that fall below RBA guidelines might be unable 

to produce the expected periodic board foot volume 

growth, which is about 200, 300, and 400 board feet/

acre/year for northern red oak site 60 (fair), 70 (good), 

and 80 (excellent), respectively, in central Appalachian 

hardwoods (Miller and Smith 1993).

Trimble and others (1974) pointed out that with 

any selection system, not all stands can be managed 

reasonably. Those with a mixture of both sawlogand pole-size trees are best suited to the initiation 

of the fi nancial maturity guidelines presented here. 

In appropriate stands, adjusting the rate of return 

(Appendix) can result in residual stands within 

the desired RBA range and may provide suffi cient 

merchantable volume marked for harvest to attract 

buyers. Mature stands that have been repeatedly highgraded may lack suffi cient growing stock with which to 

sustain subsequent harvests after all of the poor-quality 

and high-risk trees have been removed. In this case, twoage or even-age management may be more appropriate. 

Also, stands that are predominantly pole size cannot be 

managed using fi nancial maturity guidelines. For young 

stands, there are other timber management options such 

as cleaning, basal-area thinning, crop-tree management, 

and waiting. Experienced foresters can recognize these 

situations and can provide the landowner with various 

options depending on their management objectives. An 

overview of when and how to apply the FMDL method 

is found in Trimble and others (1974) and Miller and 

Smith (1993).
3

MATERIALS AND METHODS

Study Area

This study was conducted on the Fernow Experimental 

Forest (39 ̊3 ́ N, 79 ̊40 ́ W) within the Monongahela 

National Forest in north-central West Virginia. Elevations 

on the study sites range from about 2,270 to 3,160 feet 

above sea level. The average growing season is 145 days 

(May - October), and mean annual precipitation is about 

56 inches and is distributed evenly throughout the year 

(Pan and others 1997). The ecological land type of the 

Fernow is referred to as the Allegheny Sideslopes of the 

Central Appalachian Broadleaf Forest (McNab and Avers 

1994). This study encompasses six management units 

(research compartments) on 240 acres (Table 1). Each 

compartment is classifi ed as northern red oak SI 70. This 

is considered as a good site for timber production and is 

representative of much of the central Appalachian region. 

Keeping SI constant among treatments was intentional to 

avoid confounding the results by differences in potential 

site productivity. The oak SI of Schnur (1937) was 

determined for each compartment by fi eld sampling using 

the equation developed by Trimble and Weitzman (1956).

The tract of land that later became the Fernow was 

logged initially between 1903 and 1911 during the 

railroad logging era (Schuler and Fajvan 1999). During 

this period, some trees were left uncut because their size 

or form did not meet the standards of the day, or because 

the species was undesirable. The Federal Government 

purchased the land in 1915 and silviculture and 

watershed research on the Fernow began in 1933. When 

this study was initiated in 1975, some stands already had 

been treated using FMDL procedures (Table 1). Before 

1970, some stands had received a conditioning cut to 

remove culls or poorly formed old-growth residuals. 

During the 1930s, chestnut blight, fi rst noted in West 

Virginia in 1909, resulted in a reduction in standing 

timber of 25 percent on the Fernow (Weitzman 1949). 

In 1975, the research compartments in this study were 

predominantly even-aged and about 65 years old.

Species composition on the study sites is best described 

as mixed-mesophytic (Braun 1950). Common overstory 

species include northern red oak (Quercus rubra L.), 

chestnut oak (Q. prinus L.), sugar maple (Acer saccharum

Marsh.), red maple (A. rubrum L.), yellow-poplar 

(Liriodendron tulipifera L.), American beech (Fagus 

grandifolia Ehrh.), cucumbertree (Magnolia acuminata

(L.) L.), black cherry (Prunus serotina Ehrh.), basswood 

(Tilia americana L.), and white ash (Fraxinus americana

L.). Understory species composition is rich and often 

includes stinging nettle (Laportea canadensis L.), violets 

(Viola spp.), and several fern species, and is dependent on 

site and disturbance history (Gilliam and others 1995). 

Soils on the study sites are predominantly of the Calvin 

series and developed on uplands in material weathered 

from sandstone, acid red shale, and slightly calcareous red 

shale (USDA Soil Conserv. Serv. 1967). These soils are 

well drained, moderately permeable, and strongly acidic. 

Natural fertility is moderate and the average depth to 

bedrock is 32 inches.

Treatments

Three rate-of-return treatments (3, 4, and 6 percent) were 

evaluated in this study (Appendix). Each compartment 

was assigned a treatment and each treatment was 

replicated in two compartments (Table 1). Marking for 

the improvement cut (Appendix) usually occurred in 

Table 1.—History of fi nancial maturity diameter-limit cutting treatments by 

research compartment on the Fernow Experimental Forest in West Virginia 

Compartment Number

of Acres

Treatment Harvest year

Percent

26A 32.1 6 1971, 1981, 1991,2004

26B 14.2 6 1971, 1981, 1991,2004

60 31.0 4 1981, 1991,2004

20B 25.3 4 1977, 1987, 1996

31 18.9 3 1972, 1982, 1992, 2004

61 118.0 3 1983, 1993, 2004
4

tandem with marking according to the fi nancial maturity 

guidelines. Rate-of-return marking guidelines remained 

constant in each of the assigned compartments. We 

did not adjust them to achieve a more desirable RBA 

because our intent was to determine whether different 

harvest intensities were sustainable through time and 

multiple harvests by examining their effects on RBA and 

productivity. Since 1971 there have been 22 harvests 

on a planned 10-year cutting cycle. All compartments 

have been harvested at least three times and four have 

been harvested four times, though the 1973 harvest in 

Compartment 61 was not documented according to 

study protocol and could not be included in this analysis 

(Table 1).

Because this is an ongoing study and harvests are 

staggered, we do not anticipate an equal number of 

harvests in each compartment at the same time. Past 

deviations in the 10-year cutting cycle were due to 

logistical constraints in scheduling timber harvests. A 

USDA Forest Service logging crew conducted all of the 

timber harvests using conventional ground-based logging 

equipment (i.e., trees were felled by sawyers, tree-length 

logs were winched to skid roads, and logs were skidded 

to decks with rubber-tired skidders or crawler-tractors). 

Other areas on the Fernow have been treated with FMDL 

selection for demonstration purposes but have not been 

replicated and are not evaluated here.

Data Collection

At study inception, inventories of each compartment 

were conducted for all trees more than 5 inches d.b.h. 

by 2-inch class before each cutting cycle. Each tree 

was recorded by species and classifi ed as merchantable, 

cull, or dead. Most cull material was removed in the 

fi rst cutting cycle and no longer is prominent in any 

compartment. In 1986 and thereafter, permanent growth 

plots (0.5 acre) were located systematically throughout 

the compartments and replaced the 100-percent tally 

system prior to each cutting cycle so that stand structure 

and species composition could be determined. Suffi cient 

numbers of plots were installed to achieve a 10-percent 

sample in each compartment. However, all harvested 

trees have been tallied individually throughout this study 

to generate yield data. Logging crews made separate 

tallies of all trees that were not marked for cutting but 

were damaged and subsequently cut during timber 

harvesting. We now calculate the residual stand structure 

following each periodic harvest based on the 10-percent 

cruise prior to harvesting minus the harvest tally once the 

data have been standardized to a per unit area. Therefore, 

residual stand structures are estimates rather than based 

on a 100-percent tally, as in the early years of this study.

The change in data-collection procedures does not 

allow a quantitative temporal analysis of woody species 

diversity, though we do describe temporal changes in 

species composition. Seedling and sapling data have been 

collected in the past but were not collected during the 

last cycle of periodic harvests and are not evaluated here. 

Volume estimates used in our analysis were generated 

from local volume tables developed from sites throughout 

the Fernow. Originally, volume tables were constructed 

for each research compartment. In 1971, board foot 

volume tables (International 1⁄4 inch rule) were revised 

based on SI and species. All board foot volumes reported 

here were calculated on the basis of 1971 species-specifi c 

tables for northern red oak SI 70. Periodically, and most 

recently in 2002, volume tables were checked for validity; 

they continue to serve as useful estimators of actual tree 

volume based on actual scale comparisons.

Data Analysis

Repeated measures modeling using restricted maximum 

likelihood via SAS PROC MIX (SAS Inst. 2001) was 

used to evaluate treatment effects related to harvest 

period for yield in board feet/acre/year (BDFT), residual 

basal area in ft2

/acre (RBA), and percentage of grade 

1 butt logs (GRADE1) removed at each harvest. To 

maintain a balanced design, the fi rst three harvests were 

used from each compartment for analysis. When data 

from four harvests were available, we also evaluated the 

results graphically and have included them. Treatment 

level and harvest period were considered fi xed effects in 

the model. To determine the best covariance structure 

for our data, we used the Akaike Information Criteria 

(AIC) and Schwarz’s Bayesian Criterion (BIC) (Gregoire 

and others 1995; Littell and others 1996). The error 

covariance structure with the smallest values of AIC and 

BIC was considered the best model. In repeated measures 

analysis, the appropriate specifi cation of the error 

covariance structure is an important part of the model 
5

building process because measurements over time on 

the same compartments often are highly correlated. We 

included fi rst-order autoregressive (AR(1)), unstructured 

(UN), compound symmetry (CS), and spatial power 

(SP(POW)) covariance structures because these seemed 

the most appropriate from a biological perspective. The 

AR(1) error covariance structure provided the best fi t 

for modeling BDFT. In all other cases, the UN error 

covariance structure resulted in the smallest values of 

AIC and BIC and the P values reported were derived 

accordingly.

We used the Shapiro-Wilks test and graphical analysis 

to test for the assumed normality of the residuals. 

We also plotted the residuals versus the predicted 

values to graphically assess the assumption of variance 

homogeneity. The results of our tests indicated that no 

transformations were needed. We used the Tukey-Kramer 

mean separation test to examine for individual differences 

in treatment level, harvest period, and interaction terms. 

Because of the relatively low power of the experimental 

design due to less than desirable replication, the alpha 

level for signifi cance was set at 0.10 before tests of 

signifi cance were performed. We were comfortable 

using a larger than normal alpha because our results 

were derived from typical NIPF-size operational units 

with noticeable variability. Also, the consequences of 

erroneously concluding signifi cance were no greater than 

erroneously concluding no difference among treatment 

levels and harvest periods.

RESULTS

Yield

Treatment level (p = 0.0957), periodic harvest (p = 

0.0069), and the interaction of treatment level and 

periodic harvest (p = 0.0832) were signifi cant predictors 

of BDFT. The signifi cant interaction term indicates 

treatment effects vary with time and that current rates 

may continue to vary by treatment level. Most notably, 

the 6-percent treatment has deviated from the other 

treatments after repeated harvests. Mean BDFT was 319 

at the fi rst harvest for the three fi nancial maturity levels 

included in this study. BDFT increased signifi cantly at 

the second and third harvest periods but more so for the 

Table 2.—Harvested volume, residual basal area of merchantable trees (d.b.h. ≥ 11 inches), and percentage 

of grade 1 butt logs harvested (results are from the restricted maximum likelihood model and do not include 

the unreplicated harvest in 2004 from Compartment 31 (3 percent) or the fourth harvests from Compartments 

26A and 26B (6 percent)

Financial 

maturity rate

 (%)

Periodic 

harvest

Harvest volume Residual basal area Butt log grade 1 

Number Board feet/acre/yeara ft2

/acrea Percenta

6 457a 42.7a 38.2a

4 358ab 54.3a 54.2a

3 316b 51.8a 45.5a

2 422a 48.0a 50.4a

3 390a 52.1a 54.4a

1 319b 48.7a 33.1a

6 3 523a 39.1a 38.8a

6 2 511a 41.5a 45.1a

4 2 412ab 53.5a 56.9a

4 3 368ab 60.9a 69.1a

3 2 344ab 49.1a 49.1a

6 1 336ab 47.6a 30.8a

3 1 326ab 49.9a 32.0a

4 1 296b 48.6a 36.4a

3 3 278b 56.4a 55.4a

a

Means are separated within columns (α = 0.10) using the Tukey-Kramer mean comparison procedure and are designated by lower 

case letters.
6

6-percent treatment refl ecting the signifi cant 

interaction between harvest and treatment 

level (Table 2). This treatment yielded more 

than 500 BDFT during the second and third 

harvests (Table 2). This equates to a yield 

of more than 5,000 board feet/acre/decade, 

well above the expected growth and yield 

of about 3,000 board feet/acre/decade in 

managed stands. Graphical analysis shows 

that board foot yield declined to about 4,450 

acre/decade by the fourth periodic harvest 

in the 6-percent compartments but still was 

above expected productivity (Fig. 1). BDFT 

may have peaked during the second or third 

harvests (Fig. 1), though the suggested trends 

are not statistically signifi cant (Table 2). The 

3- and 6-percent guidelines have resulted in 

average harvest volumes that are meaningfully 

different within a management context. 

The 6-percent guidelines have resulted in 

merchantable harvests well above the expected 

growth, while the 3-percent guidelines 

currently are yielding somewhat less than the 

expected growth (Table 2, Fig. 1).

Residual Basal Area

Treatment effects regarding RBA were not 

signifi cantly different. The RBA of sawlogsize trees did not differ by treatment (P = 

0.5956), harvest cycle (P = 0.1578), or the 

interaction of these two factors (P = 0.5694). 

It is noteworthy that RBA model estimates 

for all but two treatment and harvest cycle 

combinations were below the recommended 

minimum of 55 ft2

/acre (Table 2). Of the 

21 documented individual harvests that 

have occurred to date in this study, only 9 

have resulted in residual basal area levels 

above 55 ft2

/acre, and none exceeded the 

recommended maximum of 70 ft2

/acre (Fig. 

2). Of the eight harvests at the 6-percent 

level, only one resulted in a residual basal 

area above 55 ft2

/acre. These results imply 

that the 6-percent level is unlikely to result 

in a residual stand within the recommended 

Figure 1.—Harvested board foot volume (International 1⁄4 inch) of 

merchantable trees (d.b.h. ≥ 11 inches) by periodic harvest and rateof-return treatment level (error bars = 1 standard error of the mean). 

Yield is presented on an annualized basis to eliminate variation 

associated with deviations in the 10-year harvest cycle. The error bar 

was intentionally omitted for the fourth periodic harvest of the 3-percent 

treatment because it has not yet been replicated.

Rate of Return (%)

346

Yield (board feet/acre/year)

0

100

200

300

400

500

600

1

2

3

4

Harvest

Figure 2.—Residual basal area of sawlog-size trees (d.b.h. ≥ 11 

inches) by periodic harvest and rate of return treatment level (error 

bars = 1 standard error of the mean). Horizontal line identifi es 

minimum residual basal area (55 ft2

/acre) as recommended by Trimble 

and others (1974). The error bar was intentionally omitted for the 

fourth periodic harvest of the 3-percent treatment because it has not 

been yet been replicated.

Rate of Return (%)

346

Residual Basal Area (feet2/acre)

0

20

40

60

80

Harvest

1

2

3

4
7

range for residual stocking. The RBA of all 

trees with a d.b.h. of 5 inches or greater did not 

differ by treatment (P = 0.4874), harvest cycle 

(P = 0.4347), or the interaction of these two 

factors (P = 0.2915). When we included polesize trees in our calculations, the mean RBA 

for all compartments through time was 75.9 

ft2

/acre (SE = 2.7, n = 21) and ranged from 94.8 

to 50.4 ft2

/acre (Fig. 3). The average difference 

in RBA between sawlog only and pole-size and 

larger trees was 25.9 ft2

/acre across all treatments 

and harvest cycles (n = 21). We do not know 

whether the substantial amount of pole-size 

RBA can mitigate the presumed less than desired 

sawlog-size RBA.

Log Grade

Estimates of GRADE1 generated by our analysis 

ranged from about 38 percent for the 6-percent 

treatment to 54 percent for the 4-percent 

treatment (Table 2), but there was no evidence 

of a statistical difference among treatments 

(P = 0.3377), harvest cycles (P = 0.1836), or the 

interaction of these two factors (P = 0.6794). 

GRADE1 model estimates were about 54 

percent for the most recent harvest cycle and 

about 33 percent for the fi rst periodic harvest. 

Graphically, when the data from the fourth 

harvest are included, it is suggested that buttlog quality has improved during the life of this 

study and that the 3- and 4-percent treatments 

produce a greater proportion grade 1 butt logs 

than the 6-percent treatment (Fig. 4).

Species Composition

Woody plant communities were complex 

and consisted of 31 commercial species. A 

comparison of beginning and ending species 

composition revealed several trends. First, 

all three treatments resulted in a decline in 

intolerant species, most notably in oak/hickory 

but also in black cherry/yellow-poplar and 

“other-intolerant” categories (Fig. 5). The latter 

included sassafras (Sassafras albidum (Nutt.) 

Nees), black locust (Robinia pseudoacacia L.), 

Figure 3.—Residual basal area of both pole-size ( 10.9 ≥ d.b.h. ≥

5 inches) and sawlog-size trees (d.b.h. ≥ 11.0 inches) by periodic 

harvest and rate-of-return treatment level (error bars = 1 standard 

error). The error bar was intentionally omitted for the fourth periodic 

harvest of the 3-percent treatment because it has not yet been 

replicated.

Figure 4.—Percentage of grade 1 butt logs harvested by periodic 

harvest and rate-of-return treatment level (error bars = 1 standard 

error). The error bar was intentionally omitted for the fourth periodic 

harvest of the 3-percent treatment because it has not yet been 

replicated.

Rate of Return (%)

346

Residual Basal Area (feet2/acre)

0

20

40

60

80

100

120

1

2

3

4

Harvest

Rate of Return (%)

346

Grade 1 Butt Logs (%)

0

20

40

60

80

1

2

3

4

Harvest
8

bigtooth aspen (Populus grandidentata Michx.), butternut 

(Juglans cinerea L.), and fi re cherry (Prunus pensylvanica

L. f.). The 6-percent treatment, which resulted in the 

lowest average RBA, showed a drop of intolerant trees 

from about 25 to fewer than 4 per acre in the 6- to 10-

inch diameter class from the fi rst to the last inventory 

cycles. The proportion of shade-intolerant species was 

not greater in the 6-percent treatment than in the other 

treatments (Fig. 5A-C).

As noted, the oak/hickory category also is in decline. 

When this study was initiated, the size-class distribution 

for oak/hickory was similar for all three treatments, 

with the smallest class consisting of the most stems and 

progressively fewer stems in larger classes. Currently, 

oak/hickory is most abundant in the 16- to 20-inch 

diameter class with progressively fewer stems in smaller 

classes, indicating that oak/hickory is responding as a 

cohort and is not being sustained as individual stems 

become older and larger (Fig. 5). As with intolerant 

species, the decline of oak/hickory is most evident in the 

pole-size class. During the fi rst inventory, oak/hickory 

ranged from 15 to 25 stems per acre in the pole class 

across all compartments. After at least three periodic 

harvests, pole-size oak/hickory ranged from four to fi ve 

stems per acre. Northern red and chestnut oak were most 

common but other species also present were white (Q. 

alba L.), scarlet (Q. coccinea Muenchh.), and black oak 

(Q. velutina Lam.), and shagbark (Carya ovata (Mill.) K. 

Koch) and bitternut hickory (C. cordiformis (Wangenh.) 

Figure 5.—Distribution of species groups by 

diameter class prior to treatment initiation 

and the last remeasurment. Segmented line 

approximates the residual stand structure 

defi ned by the BDq approach to single-tree 

selection: “q” of 1.3 (2-inch d.b.h. classes), 

a residual basal area “B” of 70 ft2

/acre for 

pole-size trees and greater (which equates 

to about 54 ft2

/acre for sawlog-size trees), 

and the largest tree to retain in the stand 

Diameter Class (inches) “D” of 26 inches d.b.h.

Begin End Begin End Begin End Begin End Begin End

0

20

40

60

80

100

120

Begin End Begin End Begin End Begin End Begin End

Trees Per Acre (no.)

0

20

40

60

80

100

120

Begin End Begin End Begin End Begin End Begin End

0

20

40

60

80

100

120

A.

B.

C.

6-10 12-14 16-20 22-26 28+

Maples 

Oak-hickory 

Cherry-poplar 

Other-tolerant 

Other-intermediate 

Other-intolerant 

3%

4%

6%
9

K. Koch). Oaks remain well represented in the sawtimber 

classes, but with average growth rates of about 2 inches 

per decade, their ultimate decline is nearly assured. 

Informal regeneration surveys indicate that this species 

group is virtually absent from the seedling and sapling 

layers in every compartment. Other species classifi ed as 

intermediate in shade tolerance include black (Betula 

lenta L.) and yellow birch (B. alleghaniensis Britton), 

slippery elm (Ulmus rubra Muhl.), cucumbertree, Fraser 

magnolia (M. fraseri Walt.), serviceberry (Amelanchier 

arborea (Michx. f.) Fern), sourwood (Oxydendrum 

arboreum L.), and white ash. Of these, black birch has 

the potential to be an interfering species in understories 

of partially disturbed canopies and was the most 

common species in the pole class when the 3-percent 

compartments were last remeasured (Fig. 5A).

Offsetting the declines noted, the density of shadetolerant species increased for all three treatments (Fig. 

5). The maples were most prominent in this category 

and commercially important sugar maple on average 

was more than twice as abundant as red maple. Polesize sugar maple averaged about 25 stems/acre across all 

compartments at the last measurement cycle. Pole-size 

American beech had about the same average density as 

red maple throughout the study area but the response of 

American beech to treatments varied considerably across 

experimental units. For example, pole-size American 

beech was abundant in Compartment 31 but nearly 

absent in Compartments 60 and 20B. Other tolerant 

species included eastern hemlock (Tsuga canadensis (L.) 

Carr.), ironwood (Ostrya virginiana (Mill.) K. Koch), 

striped maple (A. pensylvanicum L.), basswood, blackgum 

(Nyssa sylvatica Marsh.), and fl owering dogwood (Cornus 

fl orida L.). Dogwood (d.b.h. ≥ 5.0 inches) no longer 

was present in any compartment during the most recent 

inventory cycle.

DISCUSSION

Trimble and others (1974) outlined numerous issues 

to evaluate the FMDL system for managing hardwood 

stands in the central Appalachians. We address several 

of these issues here with the insight obtained after 

more than three decades of experience and empirical 

results. First, can this system of marking provide an 

adequate stand structure for approximately equal cuts 

and regular intervals? Balancing growth with removal is 

a fundamental principal of all uneven-age silviculture 

and an important component of the FMDL approach to 

regulation of timber harvests. In addressing this point, we 

reiterate that the rate of return at each periodic harvest 

was not adjusted to meet RBA goals as has been suggested 

previously by Trimble and others (1974) and Miller and 

Smith (1993). However, our results provide insight into 

the association between stocking and productivity that 

could not have been achieved otherwise.

On average, all three rate of return guidelines studied 

were at or exceeded the anticipated level of productivity 

(about 300 board feet/acre/year) for the duration of the 

study (Table 2). However, because there was a signifi cant 

interaction between the rate of return (treatment level) 

and periodic harvest (time), it is not clear whether the 

average rates of return for each treatment level can be 

sustained following additional periodic harvests at regular 

intervals. The second and third harvests generally yielded 

more merchantable volume than the fi rst harvest, but 

the fourth harvests in the 3- and 6-percent treatments 

suggest a possible downward trend in productivity (Fig. 

1). Changes in productivity over time might be related to 

several factors, including changes in species composition 

and/or stocking.

The residual stand basal area for sawlog-size trees usually 

was at the lower limit or below the recommended range 

(55 to 70 ft2

/acre) for all rates of return. Had we been 

adhering to the recommendation to lower the rate-ofreturn marking guidelines to have a minimum of 55 ft2

/

acre following harvest, the 6-percent marking guidelines 

would have been inapplicable. Conversely, there was no 

instance in which any marking guideline resulted in a 

residual stand that exceeded the recommended maximum 

RBA.

Because productivity was at or above expected levels and 

RBA generally was below a desired range, we compared 

postharvest stand structure by treatment level to residual 

stand parameters used with the BDq approach to singletree selection elsewhere on the Fernow (Fig. 5A-C) for SI 

70 (Smith and Lamson 1982). The BDq parameters used 
10

for comparison included a “q” of 1.3, a residual basal area 

“B” of 70 ft2

/acre for pole-size trees and greater (which 

equates to about 54 ft2

/acre for sawlog-size trees), and the 

largest tree to retain in the stand “D” of 26 inches d.b.h. 

Similar BDq parameters have been used for more than 

a half century in other studies on the Fernow (Schuler 

2004). Using these guidelines for comparison, the stands 

evaluated in this study had surplus trees in all but the 

largest diameter classes evaluated (22 to 26 inches d.b.h.). 

These are above the maximum in the 6-percent rateof-return and limited by prescription in the 4-percent 

rate-of-return (Fig. 5). Moreover, the RBA of pole-size 

trees and greater was at or above 70 ft2

/acre in most cases 

(Fig. 3). Our results compared to the single-tree selection 

residual stand goal suggest that the recommended RBA 

range of 55 to 70 ft2

/acre for sawlog-size trees may be 

unrealistically high when pole-size trees occupy 25 

ft2

/acre as documented in this study. RBA below 55 

ft2

/acre should be acceptable so long as productivity can 

be sustained at or above the desired levels and there is no 

signifi cant erosion of residual stand volume or butt log 

grade deterioration. RBA guidelines originally proposed 

by Trimble and others (1974) were based on expert 

opinion at that time and have not been validated.

A trend in declining residual volume after harvesting 

indicates that more volume is being removed than the 

site was capable of producing during a given cutting cycle 

and that sustainable harvest levels are being exceeded. 

Standing volume after harvest is an important element 

of the plenter system, a form of uneven-age silviculture 

used successfully in central Europe (Schütz 1999). An a 

posteriori analysis of residual standing volume revealed 

no evidence of a postharvest erosion of standing volume 

over time (Fig. 6). The 3- and 4-percent treatments 

have developed similar characteristics and have residual 

merchantable volumes of 8,000 to 9,000 board feet/acre, 

while the 6-percent treatment averaged about 6,500 

board feet/acre after the last periodic harvest. Also, 

the replicated treatments showed trends of increasing 

residual board foot volume after each periodic harvest. 

These fi ndings suggest that the originally proposed basal 

area guidelines are too high and that levels of RBA less 

than 55 ft2

/acre are acceptable and may be even closer 

to optimal with respect to periodic yield of board foot 

volume. Optimal levels of stocking for high-quality 

sawlog production have not been defi ned for mixed 

hardwood stands in the central Appalachians. Additional 

study of residual stocking is needed to increase our 

understanding of the maximum sustained yield of various 

forest products.

Equal in importance for timber management is the 

quality of sawlogs being produced. In this study, the 

proportion of trees harvested with grade 1 butt logs was 

similar to that in stands managed by single-tree selection 

(Wiemann and others 2004) and exceeded 50 percent 

for the most recent harvests in the 3- and 4-percent 

Figure 6.—Residual board foot volume 

(International 1⁄4 inch) of merchantable trees (d.b.h. 

≥ 11 inches) by periodic harvest and rate-of-return 

treatment level (error bars = 1 standard error). 

The error bar was intentionally omitted for the 

fourth periodic harvest of the 3-percent treatment 

Rate of Return (%) because it has not yet been replicated.

346

Residual Volume (board feet/acre)

0

2000

4000

6000

8000

10000

12000

1

2

3

4

Harvest
11

treatments. On the Monongahela National Forest, 

timber sales with less than half of the trees meeting 

criteria for grade 1 butt logs are reduced in value during 

the timber appraisal process. Maintaining desirable 

tree- and log-quality characteristics may be become 

more diffi cult as shade-intolerant species are depleted 

through continued periodic harvests. Throughout the 

central Appalachians, uneven-age management of any 

form postdates the establishment of even-age stands in 

virtually every case. As such, stands managed by unevenage methods retain even-aged, shade-intolerant species 

for a period of time that presumably should have better 

butt-log quality than stems of shade-tolerant species 

established in small canopy gaps. The experimental 

compartments used in this study are no exception. As 

the shade-tolerant species replace the remaining shade 

intolerants, it is reasonable to assume that butt-log 

quality may decline over time, though we found no 

evidence of this. In the future, it may be necessary to 

manage more aggressively for butt-log quality than 

current guidelines suggest. Sugar maple managed in 

uneven-aged stands has better but-log quality than sugar 

maple in unmanaged reference stands (Wiemann and 

others 2004).

The concept of FMDL selection (as well as all unevenage management) is based on the idea that desirable trees 

can be recruited and developed into larger size classes 

through repeated harvests. This requires having desirable 

species that can survive and grow in an environment 

dominated by relatively small canopy gaps created by 

the harvesting of mostly single trees and the creation 

of small openings. In the 1970s it was understood that 

uneven-age management using single-tree selection could 

achieve adequate regeneration and development of both 

red and sugar maple and American beech (Trimble and 

others 1974; Smith 1980). It was not known whether 

the FMDL guidelines tested in this study would result 

in the unplanned creation of openings large enough 

to recruit and sustain a greater proportion of shadeintolerant species that initially dominated the canopies 

of these stands. Our results point out that even with 

RBA below what has been previously recommended, the 

preponderance of stems reaching pole size are shadetolerant species. Not even the 6-percent treatment 

deviated from this trend; thus, it is expected that 

over time the FMDL guidelines will result in stands 

dominated by shade-tolerant species.

Since shade-tolerant species are the predominant group 

moving into the pole class, the question is whether these 

species are acceptable. Sawlog prices in the West Virginia 

Timber Market Report (www.ahc.caf.wvu.edu, 26 June 

2006) for the fi rst quarter of 2006 indicate that shadeintolerant black cherry was the State’s highest valued 

species during the reporting period at $710 per thousand 

board feet (Mbf), but sugar maple was the second highest 

valued species ($417/Mbf) and somewhat greater than 

red oak ($297/Mbf). Red maple listed as soft maple 

($206/Mbf) was greater than white oak ($163/Mbf). 

Yellow-poplar, a common shade-intolerant species, 

was listed at $129/Mbf. Current stands with equal 

proportions of sugar and red maple would be valued at 

$312/Mbf while stands with equal proportions of black 

cherry, red and white oak, and yellow-poplar would be 

valued at $325/Mbf. Thus management efforts that favor 

preferred shade-tolerant species can be competitive with 

efforts that favor shade-intolerant species based on recent 

stumpage values.

Historically, prices for soft maple have been less than 

oak and it is not known how long the relative equality 

between the oaks and maples will persist. However, it 

is well known that oaks are diffi cult to regenerate in 

the central Appalachians, so the choices for many land 

managers are essentially between the shade-tolerant 

maples and beech, or the shade-intolerant suite of 

species. If the stand characteristics associated with evenage management and clearcutting are unacceptable, 

the potential species and associated stumpage prices 

associated with uneven-age management are a reasonable 

alternative. For example, using the stands observed here 

with average productivity for the 4-percent treatments 

(3,580 board feet/acre/decade), expected revenues 

(assuming $312/Mbf for the average maple stumpage 

value) on a 40-acre parcel (SI = 70) would be about 

$45,000 per decade.

The FMDL guidelines cannot provide a long-term 

solution to the regulation of merchantable harvest 

if undesirable species are allowed to dominate the 

regeneration and eventually dominate the stand. In this 
12

study, American beech represented more than 30-percent 

of all pole-size stems in one of six compartments so 

treatment is needed to reduce this percentage. American 

beech may be able to provide some mast production in 

stands using uneven-age management but this is a lowvalue commercial species with a bleak future due to beech 

bark disease (Houston 1994). American beech and striped 

maple also interfere with the establishment of more 

valuable species (Nyland and others 2006). Kochenderfer 

and others (2004) developed recommendations for 

preharvest manual herbicide treatments to control 

unwanted beech. Average application costs were less 

than $40/acre when treating as many as159 pole-size 

stems/acre. Treating pole-size trees with stem-injected 

glyphosate also controlled half of the small understory 

American beech stems. When American beech dominates 

the understory in stands that are partially cut, it is likely 

to be the dominant regeneration after the harvesting is 

completed (Leak 1988; Bohn and Nyland 2003). Nyland 

and others (2006) recommend controlling undesirable 

advance regeneration with herbicides if more than 30 to 

40 percent of the area has competitive beech or striped 

maple.

CONCLUSION

Using a silvicultural practice that provides a continuous 

output of desired products without degrading the site 

for future productivity is a basic tenet of sustainable 

forestry. In this study, our objective was to determine 

if FMDL selection can sustain the production of highquality sawlog timber. We evaluated periodic board foot 

yield, residual basal area, percentage of grade 1 butt logs, 

and species composition over time. On the basis of the 

combined results to date, we believe that the fi nancial 

maturity diameter-limit method can be sustainable if 

applied appropriately. Unlike earlier recommendations, 

we believe that a minimum RBA of about 45 ft2

/acre in 

sawlog-size trees is acceptable on good sites (northern 

red oak SI 70) without eroding the potential to maintain 

harvest intervals and volumes, presuming about 20 

ft2

/acre of desirable pole-size trees is also present. 

Research is needed to refi ne guidelines for desired residual 

stocking for all site indices. Our results suggest that the 

6-percent treatment and possibly other treatments may 

not be feasible with earlier recommendations regarding 

minimum RBA of sawlog-size trees.

Combining the FMDL guidelines with treatment of 

interfering regeneration would addresses certain concepts 

of sustainable forestry. Improving on the common 

form of diameter-limit harvesting using the procedures 

described here would be a signifi cant step in improving 

forest management throughout the Eastern United States. 

ACKNOWLEDGMENTS

Long-term studies such as this one require institutional 

backing and the commitment of many individuals to 

succeed. We thank the following Northern Research 

Station employees for essential contributions: H. Clay 

Smith (retired), Gary Miller (Morgantown, WV), Robert 

Rosier (retired), Richard Hovatter, Donnie Lowther, and 

Frederica Wood. Also, Scott Hockman, Mark Owens, 

and Jeff Pennington safely harvested many of the study 

areas in recent years. Eric Heitzman (West Virginia 

University) and Laura Kenefi c (Orono, ME) provided 

helpful technical reviews, and John Stanovick (Newtown 

Square, PA) provided guidance with the statistical 

procedures.

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16

APPENDIX

Marking Guidelines for FMDL Method by Rate-of-Return, Northern Red Oak SI, and Species

Mark trees of these 2-inch d.b.h. classes and largera

Low return

(2%)

Medium-low 

return

(3%)

Medium return

(4%)

Medium-high 

return

(5%)

High return

(6%)

SI 

80

SI 

70

SI 

60

SI 

80

SI 

70

SI 

60

SI 

80

SI 

70

SI 

60

SI 

80

SI 

70

SI 

60

SI 

80

SI 

70

SI 

60

Species

Yellow-poplar 26 26 24 24 22 22 20 18 18 20 18 18 18 18 18

Beech 24 22 22 22 20 20 20 18 18 20 18 18 18 18 18

Black cherry 32 30 30 28 26 24 22 20 18 20 20 18 18 18 18

Red maple 32 30 30 28 26 24 22 22 18 20 20 18 18 18 18

White ash 30 28 28 26 24 24 22 20 18 20 20 18 18 18 18

Sugar maple 32 32 30 28 28 24 22 22 18 20 20 20 20 18 18

Red oak 26 26 24 24 24 22 22 22 20 22 20 20 20 18 18

White oak 24 22 20 22 20 20 20 18 18 20 18 18 18 18 18

Chestnut oak 24 24 22 22 22 20 20 18 18 20 18 18 18 18 18

Other long-lives species 26 26 24 24 24 22 20 20 18 20 20 18 18 18 18

a

 These trees will be marked unless a potential grade improvement can be foreseen in the next 10 years.

Improvement cut for all situations, mark (above 11 inches d.b.h.):

1. Culls and near culls (50 percent rot or nearly so in the butt log).

2. Trees with signifi cant rot in the butt log (e.g., 40 percent and will increase to cull status 

by next periodic cut).

3. Very low-vigor trees.

4. Extremely rough trees with butt-log grade 5 (i.e., pallet and local use sawtimber).

5. Any tree more than 15 inches d.b.h. with butt-log grade 4 (i.e., unable to qualify as a 

grade 3 due to form defects but no rot).

6. Any short-lived species (e.g., black locust, sassafras, and butternut, unless it is unusually 

vigorous).
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Schuler, Thomas M.; McGill, David W. 2007. Long-term assessment of financial 

maturity, diameter-limit selection in the central Appalachians. Res. Pap. 

NRS-2. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, 

Northern Research Station. 16 p.

Financial maturity, diameter-limit (FMDL) selection was proposed more than three 

decades ago as a replacement for diameter-limit cutting. FMDL incorporates 

financial maturity guidelines for individual trees, high-priority removal of poorquality trees, and guidelines for residual basal area. We provide the first long-term 

assessment of this practice after more than three decades of implementation. 

FMDL selection is evaluated in terms periodic yield of merchantable board feet, 

residual basal area, butt-log quality, and species composition. Recommendations 

for lowering the minimum residual basal area are presented. Management 

implications regarding controlling species composition are discussed.

KEY WORDS: Quercus rubra, Acer saccharum, uneven-age management, partial 

cutting 
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